Method of determining a lighting situation

TECHNICAL FIELD

The invention concerns a method of determin ing a lighting situation with regard to the directiona lity of the light, as well as a device and an arrangement for use in said method according to the preambles of the independent claims.

BACKGROUND ART

Determination of the lighting situation, e.g. hard light or soft light, in particular directional sun light (sunshine) or diffuse sunlight (cloudy sky), can be usefully employed in many different applications.

For example in the field of building automa tion it can serve to automatically operate shading devi ces, like awnings or blinds, in order to prevent a buil ding from extensively heating up when the sun is shining and to expose it to full light when the sky is cloudy.

Also for statistical investigations, for weather forecast services or for the prediction of the power production of a photovoltaic plant an automated determination of the light exposure situation at specific locations can be useful.

Since overexposure to sunlight for humans may have several detrimental effects, like e.g. sunburn, ra pid skin ageing or even skin cancer, an automated deter mination or monitoring, respectively, of the sunlight ex- posure of a person during the day might also be expedient in order to inform the person about his or her exposure situation and/or warn him or her in case of overexposure.

However, the methods and devices known today for automated determination of the lighting situation are based on digital camera technology, and thus the equip ment employed in performing these methods is expensive, damageable and bulky, which is the reason that numerous meaningful applications are not realized today.

DISCLOSURE OF THE INVENTION

Hence, it is a general object of the inven tion to provide technical solutions which do not have the before described disadvantages of the prior art or at least partially avoid them.

This object is achieved by subjects of the independent claims.

A first aspect of the invention concerns a method of determining a lighting situation with regard to the directionality of the light, e.g. determining if the light at a location is hard light, where the light rays are mostly parallel, (directional light generating high contrasts and clearly distinguishable shadows with hard edges) or soft light (non-directional or diffuse light generating no shadows or diffuse shadows with soft ed ges), in particular directional sunlight (sunshine) or diffuse sunlight (cloudy sky) .

According to the method, several preferably identical photosensitive elements, in particular photo voltaic cells or photodiodes, are provided, the maximum photo signal or the maximum power yield of which in directional light is achieved at a specific optimum angle of impact of the light onto the light absorbing surface of the photosensitive element and increasingly decreases with an increasing deviation from said optimum angle.

The term "photo signal" here is associated with passive photosensitive elements, like e.g. photodiodes, while the term "power yield" is associated with active photosensitive elements, like e.g. photovoltaic cells. The several photosensitive elements can all be passive elements, all be active elements or can consist of passive and active elements.

These photosensitive elements are arranged relative to each other in such a manner that they require different directions of directional light in order to be hit by said directional light in their respective optimum angle of impact. This arrangement of photosensitive elements, in particular photovoltaic cells or photodiodes, is exposed to light.

Depending on the degree of directionality of the light the arrangement of photosensitive elements is exposed to, the photo signals or power yields of the in dividual photosensitive elements of the arrangement more or less strong differ from each other. The higher the degree of directionality, the bigger the difference bet ween the individual photo signals or power yields. Depen ding on the intensity and spectrum of the light the ar rangement of photosensitive elements is exposed to, the absolute level of the photo signals or power yields of the individual photosensitive elements, and in particular of the photo signal or power yield of the photosensitive element of the arrangement which is providing the highest lighting photo signal or highest power yield of all pho ^¬ tosensitive elements, will be higher or lower.

For example, if the arrangement of photosen sitive elements is exposed to very strong directional light, e.g. sunshine from a blue sky, the photo signals or power yields of the individual photosensitive elements will be quite different and the absolute level of the photo signal or power yield of the photosensitive element with the highest lighting photo signal or highest power yield will be quite high. If, for example, the arrangement of photosensitive elements is exposed to strong diffuse light, e.g. sunlight from a cloudy sky, the photo signals or power yields of the individual photosensitive elements will be quite equal and their absolute level will be high. If the arrangement is exposed to light in the shadow, depending from the situation (blue sky or cloudy sky) , the photo signals or power yields of the in ^¬ dividual photosensitive elements will be quite equal or differ to a certain extend and the absolute level of the photo signals or power yields of the photosensitive ele ments will be medium to low.

In the method according to the invention, the photo signals or power yields of the individual photosen sitive elements of the specific arrangement, i.e. the differences between their levels, are used to determine the lightning situation at the location where the arrangement of photosensitive elements, in particular pho tovoltaic cells or photodiodes, is exposed to the light with regard to directionality of the light.

By doing so it is possible to determine a lighting situation with regard to the directionality of the light in an automated manner with non-expensive, small and robust equipment.

In a preferred embodiment of the method, the degree of directionality of the light the arrangement of photosensitive elements is exposed to is determined from the relative differences between their photo signals or power levels, i.e. from the variation of the different photo signals or power yields of the individual photosen- sitive elements, often also termed as photo current. Such a degree of directionality can for example be expressed as a grade on a predefined scale starting with no direc ^¬ tionality (the photo signals or power yields of all pho tosensitive elements are equal) and ending with a maximum detectable directionality (maximum possible difference between the photo signals or power yields of two of the photosensitive elements) or a percentage of the maximum possible difference between the photo signals or power yields of two of the photosensitive elements.

Preferably, by doing so it is determined if the arrangement of photosensitive elements, in particular photovoltaic cells or photodiodes, is exposed to hard light or to soft light, e.g. by comparing the determined degree of directionality of the light with predefined threshold values or value ranges for hard light and soft light . In a preferred embodiment of the method, the photosensitive elements are exposed to sunlight and from the differences between the levels of the different photo signals or power yields of the individual photosensitive elements, i.e. from the variation of the different photo signals or power yields, it is determined if the photosensitive elements are exposed to directional sunlight, i.e. sunshine from blue sky, or to diffuse sunlight, i.e. sunlight from a cloudy sky.

When doing so, it is furthermore preferred to determine from the levels of the photo signals or power yields of the individual photosensitive elements if the arrangement of photosensitive elements is exposed to sun light from a blue sky or to sunlight from a cloudy sky, with direct exposure or in the shadow. This can for exam ple be done as follows:

If there is an extreme scatter between the photo signals or power yields of individual photosensi tive elements (e.g. the level of the lowest photo signal or power yield is less than 50% of the level of the highest photo signal or power yield), i.e. extreme degree of directionality and thus very hard light, and the level of the highest photo signal or power yield is quite high (e.g. more than 70% of maximum possible photo signal or power yield) , it is determined that the arrangement of photosensitive elements is directly exposed to sunshine.

The term "maximum possible photo signal or power yield" used here above and in the following text designates an expected photo signal or power yield of the respective photosensitive element maximally achievable in the intended use, e.g. the photo signal or power yield which is expected to be achievable with the respective photosensitive element at the maximum sunlight intensity known on earth. It is a component-specific threshold value of the photosensitive element. If there is considerable scatter between the photo signals or power yields of individual cells (e.g. the level of the lowest photo signal or power yield is less than 50% of the level of the highest photo signal or power yield), i.e. an elevated degree of directionality which is closer to hard light than to soft light, and the level of the highest photo signal or power yield is medium high (e.g. between 30% to 50% of the maximum possible photo signal or power yield), i.e. medium light intensity, it is determined that the arrangement of photosensitive elements is exposed to sunlight under a sunshade with the sun shining from a blue sky.

If there is no or little scatter between the photo signals or power yields of individual cells (e.g. the level of the lowest photo signal or power yield is more than 90% of the level of the highest photo signal or power yield), i.e. low degree of directionality and thus quite soft light, and the level of the highest photo signal or power yield is quite high (e.g. more than 60% of the maximum possible photo signal or power yield) , it is determined that the arrangement of photosensitive elements is exposed to sunlight under a cloudy sky.

If there is no or little scatter between the photo signals or power yields of individual cells (e.g. the level of the lowest photo signal or power yield is more than 90% of the level of the highest photo signal or power yield), i.e. a low degree of directionality and thus soft light, and the level of the highest photo signal or power yield is medium high (e.g. between 30% to 50% of the maximum possible photo signal or power yield) , i.e. medium light intensity, it is determined that the arrangement of photosensitive elements is exposed to sunlight under a sunshade and with a sky full of clouds.

In a preferred embodiment of the method, the provided photosensitive elements, in particular photovol taic cells or photodiodes, have an optimum angle of im ^¬ pact of the light onto their light absorbing surface of 90°, i.e. in order to provide a maximum photo signal or power yield from directional light they are exposed to, this light must perpendicularly impact onto their light absorbing surfaces. In this embodiment, the photosensitive elements are arranged in such a manner that their light absorbing surfaces are at an angle to each other.

By this it can be ensured that the photosen sitive elements require different directions of direc tional light in order to be hit by said directional light in their respective optimum angle of impact.

In another preferred embodiment of the me thod, the provided photosensitive elements have an opti mum angle of impact of the light onto the light absorbing surface of less than 90°, i.e. in order to provide a ma ximum photo signal or power yield from directional light they are exposed to, this light must not perpendicularly impact onto the light absorbing surface of the photosen sitive element but at another specific angle. In this embodiment, the photosensitive elements are arranged in such a manner that their light absorbing surfaces extend in one common plane or extend in several parallel planes. The orientation of the photosensitive elements relative to each other in said plane or planes however is made such that the photosensitive elements require different directions of directional light in order to be hit by said directional light in their respective optimum angle of impact.

In still another preferred embodiment of the method, the photosensitive elements which are provided have an optimum angle of impact of the light onto the light absorbing surface of 90°, i.e. in order to provide a maximum photo signal or power yield from directional light they are exposed to, this light must perpendicularly impact onto their light absorbing surfaces. In this embodiment, optical means are provided in the light tra velling path to the light absorbing surface of the respective photosensitive elements which deflect the direc- tional light before it reaches the light absorbing sur face of the photosensitive elements. The photosensitive elements in this embodiment are arranged in such a manner that their light absorbing surfaces extend in one common plane or extend in several parallel planes. The orien tation of the optical means however is made such that different directions of directional light are required in order to hit the photosensitive elements by said direc tional light in their respective optimum angle of impact.

Preferably, the optical means are provided directly on the light absorbing surfaces of the photo sensitive elements, preferably in the form of diffractive optical surface structures.

The embodiments of the method in which the light absorbing surface of the respective photosensitive elements are arranged in one common plane or in several parallel planes have the advantage that a very flat arrangements of photosensitive elements can be used in performing the method.

In another preferred embodiment of the method according to the invention, the photosensiti e elements, in particular photovoltaic cells or photodiodes, are arranged on an object or on a person, in order to determine the lighting situation of said object or person. Especi ally for movable objects and persons this has the advan tage that the photovoltaic elements automatically are mo ved with the object or person, and thus always are avail able for performing the method.

Preferably, the photosensitive elements are arranged on the object or person at defined positions and/or in defined orientations with respect to each other. This has the advantage that, due to the known relative positions and/or orientations, quite precise determinations of the lighting situation become possible.

By advantage, the photosensitive elements, in particular photovoltaic cells or photodiodes, are arranged on the object or person on a common supporting struc- ture, so that they all together with the supporting structure can be easily attached to and detached from the object or person.

In a first preferred variant, the supporting structure is a piece of clothing. In this variant it is furthermore preferred that the photosensitive elements are arranged at different locations on the piece of clothing, for example randomly or at defined positions and/or in defined orientations with respect to each other .

In a second preferred variant, the supporting structure is a piece of jewelry or a wristwatch.

In a third preferred variant, the supporting structure is a button or sticker attached or attachable, respectively, to a piece of clothing.

In a further preferred embodiment, the method according to the invention is part of a method of estimating the quantity of UV-radiation an object or a person is exposed to and/or has been exposed to over a certain span of time.

Due to the UV-radiation in the sunlight, overexposure to sunlight for humans has several detrimen tal effects, like e.g. sunburn, rapid skin ageing or even skin cancer. Every year millions of people are diagnosed with skin cancer, mainly due to the UV-radiation in the sunlight .

A basic problem is that humans do not have direct sense for UV-radiation, which is not visible for them, and thus often cannot judge their exposure to UV- radiation and the effects and risks encountered there with .

In order to facilitate a meaningful exposure to sunlight, mobile UV measuring devices have been devel oped and are commercially available by means of which the actual intensity of UV-radiation and often also the accu mulated amount of UV-radiation over a certain exposure time can be determined. Especially for people with skin cancer such devices are of great help in order to reduce exposure to UV-radiation and therewith increase their prospects of recovery.

For evaluating the total exposure to UV-radiation of a person as precise as possible, the person has to carry the UV measuring device all day long, and at a place of the body where it is always exposed to any light the person is exposed to. This calls for devices which are as inconspicuous and small as possible and do not require any maintenance. The target in today's devel opments is to provide UV measuring devices with a size and with an autonomy that enables them to become part of the clothing of a person, e.g. in the form of a button or sticker, so that they are not recognized as devices any more by the user and by other persons.

To be as autonomous as possible, almost all of the available mobile UV measuring devices are equipped with photovoltaic cells, which charge an energy storage (capacitor or accumulator) from which the device obtains the energy for its operation.

For measuring the UV-radiation in the sunlight, different concepts are known in the art.

Some of the known UV measuring devices use special UV-sensors on the basis of aluminium gallium nitride, gallium nitride or silicium carbide, which how ever are quite expensive compared to sensors for measuring radiation in the visible range of sunlight. In order to save costs, in most applications sensors having a very small sensing surface are employed, resulting in a weak signal that needs to be amplified quite extensively in order to be convertable into a digital signal and thus a low signal-to-noise-ratio results which in turn does not allow for a precise measurement.

Other known mobile UV measuring devices use sensors which are sensitive to visible radiation in com ^¬ bination with special optical filters for measuring the UV-radiation in the sunlight. US 5,382,986 A for example discloses sunglas ses with an integrated UV measuring device using two identical photodiodes the sensitive areas of which are covered by different optical band-pass filters, one that transmits only UV-A radiation and one the transmits both, UV-A and UV-B radiation.

From US 7,271,393 B2 , an UV measuring device is known which for measuring the UV-radiation in the sun light uses two identical visible light sensors, one of which is covered by a filter that changes its transmis- sibility for visible radiation as a function of the UV- radiation it is exposed to.

US 5,151,600 A discloses a noseshade for monitoring the exposure to UV-radiation. Here, for measuring of the UV-radiation two photovoltaic cells are em ployed which are covered by different optical band-pass filters, transmitting the UV-A and UV-B radiation, res pectively.

All the afore mentioned known concepts have the disadvantage that they require quite sophisticated equipment for determining the UV-radiation and that in case the UV-measuring device shall be autonomously power ed by sunlight, beside the surface area needed for sen sing the UV-radiation additional equally exposed surface areas on the device are needed for generating electrical power. This, however, quite considerably limits the po tential for further miniaturization of such devices in order to allow them to become part of the closure of a person, e.g. in the form of a button or sticker.

These disadvantages are overcome by the fol lowing preferred variant of the last mentioned embodiment of the method according to the invention. In this vari ^¬ ant, the local position of the object or person is deter mined, based on that determined local position, a data source is chosen which provides UV-radiation data for the region of said local position, and based on the determin ^¬ ed lighting situation of the photosensitive elements, in particular photovoltaic cells or photodiodes, (exposure to sunshine from blue sky or to sunlight from a cloudy sky, direct exposure or shadow) and the UV-radiation data provided by said data source, the quantity of UV-radiation the object or person is exposed to and/or has been exposed to over a certain span of time is estimated.

Thus, by monitoring the lighting situation of the object or person and obtaining information about the UV-radia tion at the location of the object or person from an external source, the quantity of UV-radiation the object or person is exposed to and/or has been exposed to over a certain span of time is estimated, without any need to perform any quantitative UV-radiation measurements.

Preferably, this is done in that the photo sensitive elements, in particular photovoltaic cells or photodiodes, are part of one or several mobile devices by means of which data representing the lighting situation of the object or person are transmitted to a receiving unit, preferably in a wireless manner, e.g. by Bluetooth, which receiving unit determines the local position, based on that determined local position chooses the data source which provides UV-radiation data for the region of said local position and, based on the determined local posi tion, the determined lighting situation and the UV-radiation data provided by said data source, estimates the quantity of UV-radiation the object or person is exposed to and/or has been exposed to over a certain span of time .

If the photosensitive elements used for the determination of the lighting situation are photovoltaic cells and at least a part of them are furthermore used for generating electrical power for said one or several mobile devices, such devices can be quite tiny because no additional light exposed surface area on them is required for generating electrical power.

As external data source for providing UV-ra ^¬ diation data for the region of the local position of the object or person or of the local position of the recei ving unit, preferably a meteorological station (weather station) in the region of said local position is chosen. Such meteorological stations can provide quite accurate UV-radiation data, which can be made accessible via the Internet .

Preferably, the estimated quantity of UV-ra diation the object or person is actually exposed to and/or has been exposed to over a certain span of time is made recognizable by means of the receiving unit to a user .

If the receiving unit is a mobile phone, preferably a smart phone with an App adapted to estimate and make recognizable the quantity of UV-radiation the object or person is actually exposed to and/or has been exposed to over a certain span of time, this can be done in a convenient and inconspicuous manner.

Generally it is preferred that in the method according to the invention it is furthermore determined if the light the photosensitive elements, in particular photovoltaic cells or photodiodes, are exposed to contains UV-radiation. By this, it is possible to distin guish between lighting situations caused by natural light (sunlight), which typically contains a substantial amount of UV-radiation, and artificial light, which typically contains no or only very weak UV-radiation.

Thus, in case the method is part of a method of estimating the quantity of UV-radiation an object or a person is exposed to and/or has been exposed to over a certain span of time, it is preferred that based on the result of the determination of the quantity of UV-radiation it is determined if the object or person is exposed to sunlight or to artificial light.

In that case it is furthermore preferred that only if the determination reveals that the object or person is exposed to sunlight or for the relevant span of time has been exposed to sunlight, the estimation of the quantity of UV-radiation the object or person is exposed to and/or has been exposed to over a certain span of time is performed.

In a further preferred embodiment of the method, in which the photosensitive elements, in particular photovoltaic cells or photodiodes, are arranged at a mobile object or a person, the variations of the photo signal or power yields of the individual photosensitive elements over time are determined. From these variations it is possible to determine if the object or the person the photosensitive elements are arranged at is in motion or is stationary, which is furthermore preferred. This can be done as follows:

If the individual photo signals or power yields of the individual photosensitive elements consi derably vary within short periods (e.g. more than 30% within some seconds), it is determined that the person or object is in motion. If there are no variations or only small ones within short time periods, it is determined that the person or object is stationary.

In still a further preferred embodiment of the method, in which the photosensitive elements are arranged at a mobile object or a person, in addition to the photosensitive elements there is arranged at the object or person at least one temperature sensor for sensing the ambient temperature near the photosensitive elements. The photosensitive elements, in particular photovoltaic cells or photodiodes, and the temperature sensor are, together with the object or person they are arranged at, outdoors exposed to sunlight, and by means of the temperature sensor the ambient temperature near the photosensitive elements is determined, in particular the course of the ambient temperature near the photosensitive elements over a certain period.

When doing so, it is furthermore preferred to determine the local position of the object or person, to choose, based on that determined local position, a data source which provides ambient temperature data for the region of said local position, and to compare the deter mined ambient temperature near the photosensitive ele ments or the determined of the course ambient temperature near the photosensitive elements, respectively, with the ambient temperature data provided by said data source.

Preferably, in the last two embodiments the method is part of a method of supporting a person using a sunscreen product in determining the point in time for the next application of the product or the application interval .

In a preferred variant, in which it is determined that the person is in motion, the remaining time until the next application is reduced compared to a sta tionary situation, since the sunscreen product is more rapidly degraded or worn off, respectively, by friction (clothing) and sweating, which are effects typically associated with active motion.

In a further preferred variant, in which it is determined that the ambient temperature near the pho ^¬ tosensitive elements over a certain period has been sig nificantly above or below an ambient temperature derived from the ambient temperature data for the region of said local position provided by said data source, the remaining time until the next application is reduced compared to a situation in which both are more or less equal be ^¬ cause of the following assumptions:

If the determined ambient temperature near the photosensitive elements, in particular photovoltaic cells or photodiodes, has for a certain period been sig ^¬ nificantly (e.g. more than 5° C) below the ambient tempe ^¬ rature derived from the ambient temperature data provided by said data source, it is assumed that the person was in the water and thus the sunscreen product has been removed by the water.

If the determined ambient temperature near the photosensitive elements, in particular photovoltaic cells or photodiodes, has for a certain period been sig nificantly (e.g. more than 5° C) above the ambient temperature derived from the ambient temperature data provided by said external data source, it is assumed that the per son was exposed for a longer period to direct sunshine and thus the sunscreen product has been degraded or remo ved by sweating.

Moreover, the temperature sensor can help to determine if the lighting situation that is determined is short term or long term. I.e. if the device is exposed to direct sun long term it will heat up. If it is in the shadow long term it will determine the same temperature as provided by the external data source.

D second aspect of the invention concerns a device for use in performing of the method according to the first aspect of the invention.

The device comprises several preferably identical photosensitive elements, in particular photovoltaic cells or photodiodes, the maximum photo signal (passive photosensitive elements, like e.g. photodiodes) or power yield (active photosensitive elements, like e.g. photo voltaic cells) of which in directional light is achieved at a specific optimum angle of impact of the light onto the light absorbing surface of the photosensitive ele ments and increasingly decreases with an increasing de viation from said optimum angle.

It furthermore comprises a supporting struc ture, on which said photosensitive elements are arranged in such a manner that they require different directions of directional light in order to be hit by the light in their respective optimum angle of impact.

The device also comprises one or several transmitting units, by means of which data representing or derived from the different photo signals or power yields of the individual photosensitive elements can be transmitted to a receiving unit, in preferably in a wireless manner, e.g. by Bluetooth. Such devices can be provided at considerably low costs and can be of sturdy design.

In a first preferred embodiment, the device comprises exactly one transmitting unit by means of which data representing or derived from the different photo signals or power yields of the individual photosensitive elements, in particular photovoltaic cells or photodiodes, can be transmitted to a receiving unit. Thus, there is a common transmitting unit for all the photosensitive elements. This embodiment has the advantage that only one transmitting unit is required which allows for very cost- effective solutions, but it requires however that all photosensitive elements are arranged close to the recei ving unit, thereby limiting the freedom of choice with regard to the supporting structure used and the placement of the photosensitive elements thereon.

In a second preferred embodiment, the device comprises several transmitting units, each of which is dedicated to one or several of the photosensitive ele ments, by means of which in each case data representing or derived from the photo signal or power yield of the one photosensitive element or the photo signals or power yields of the several individual photosensitive elements can be transmitted to a receiving unit. Thus, in this em bodiment every photosensitive elements has its own trans mitting unit or there are groups of photosensitive ele ments, in each case having a common transmitting unit for the photosensitive elements of that group, so that the device in fact is formed by several sub-devices capable of transmitting data representing or derived from the different photo signals or power yields of the individual photosensitive elements to a common receiving unit. This embodiment has the advantage that it offers a great free ^¬ dom of choice with regard to the supporting structure used and the placement of the photosensitive elements thereon. However, it is more costly than the before men ^¬ tioned embodiment. By advantage, the photosensitive elements are arranged at the supporting structure at defined positions and/or in defined orientations with respect to each other. By this, the interpretation of the different photo signals or power yields is facilitated and thus a reliab le determination of the lighting situation becomes possi ble, in particular if the photosensitive elements are arranged next to each other.

The supporting structure in one preferred em bodiment of the device is a piece of clothing, e.g. a T- shirt or a sunhat, wherein in a further preferred variant of this embodiment, the photosensitive elements, in particular photovoltaic cells or photodiodes, are arranged at different locations at the piece of clothing, at defi ned positions and/or in defined orientations with respect to each other or randomly. In another preferred embodiment, the supporting structure is a piece of jewelry or a wristwatch. In yet another preferred embodiment, the supporting structure is a button or sticker for attachment to a piece of clothing. Such supporting structures have the advantage that they can be easily attached to and detached from a person.

In a further preferred embodiment of the de vice, the photosensitive elements have an optimum angle of impact of the light onto the light absorbing surface of 90°, i.e. in order to provide a maximum photo signal or power yield from directional light they are exposed to, the light must perpendicularly impact onto their light absorbing surfaces. In this embodiment, the photo ^¬ sensitive elements are arranged at the supporting struc ^¬ ture in such a manner that their light absorbing surfaces are at an angle to each other. By this it can be ensured that the photosensitive elements require different direc tions of directional light in order to be hit by said directional light in their respective optimum angle of impact . In another preferred embodiment of the device, the photosensitive elements have an optimum angle of impact of the light onto the light absorbing surface of less than 90°, i.e. in order to provide a maximum photo signal or power yield from directional light they are exposed to, the light must not perpendicularly but at another specific angle impact onto the light absorbing surface of the photosensitive element. In this embodi ment, the photosensitive elements are arranged at the supporting structure in such a manner that their light absorbing surfaces extend in one common plane or extend in several parallel planes. The orientation of the photo sensitive elements relative to each other in said plane or planes however is made such that the photosensitive elements require different directions of directional light in order to be hit by said directional light in their respective optimum angle of.

In still another preferred embodiment of the device, the photosensitive elements have an optimum angle of impact of the light onto the light absorbing surface of 90°, i.e. in order to provide a maximum photo signal or power yield from directional light they are exposed to, the light must perpendicularly impact onto their light absorbing surfaces. In this embodiment, optical means are provided in the light travelling path to the light absorbing surface of the respective photosensitive element which deflect the directional light before it reaches the light absorbing surface of the photosensitive element .

Preferably, the photosensitive elements in that embodiment are arranged in such a manner that their light absorbing surfaces extend in one common plane or extend in several parallel planes. The orientation of the optical means however is made such that different directions of directional light are required in order to hit the photosensitive elements by said directional light in their respective optimum angle of impact. Preferably, the optical means are provided directly on the light absorbing surfaces of the photosen sitive elements, preferably in the form of diffractive optical surface structures.

The embodiments of the device in which the light absorbing surface of the respective photosensitive elements are arranged in one common plane or in several parallel planes have the advantage that a very flat devi ces become possible.

In a further preferred embodiment, the device is designed such that its photosensitive elements are photovoltaic cells and that at least a part of these pho tovoltaic cells can furthermore be used for generating electrical power for the operation of the device. By this, the advantage is arrived at that no additional light exposed surfaces are required at the device for generating power for its operation, and thus quite small devices according to the invention become possible.

In still a further preferred embodiment, the device furthermore comprises means for determining UV- radiation. Preferably, it is designed such that at least some of the photosensitive elements which are used for the determination of the lighting situation are also used for determining UV-radiation . This has the advantage that no additional light exposed surfaces are required at the device for determining the UV-radiation, and thus quite small devices according to the invention become possible.

In still a further preferred embodiment, the device furthermore comprises at least one temperature sensor for determining the ambient temperature near the photosensitive elements.

In the last two preferred embodiments it is furthermore preferred that the one or several transmit ting units are adapted for also transmitting data repre ^¬ senting or derived from the determination of UV-radiation and/or the determination of the ambient temperature near the photosensitive elements, in particular photovoltaic cells or photodiodes, to the receiving unit.

A third aspect of the invention concerns an arrangement, in particular for performing the method ac cording to the first aspect of the invention, comprising a device according to the second aspect of the invention and a receiving unit capable of receiving the data representing or derived from the different photo signals or power yields of the individual photosensitive elements, in particular photovoltaic cells or photodiodes, of the device and capable of determining, based on said data, the lighting situation with regard to the directionality of the light to which the device is exposed.

Preferably, the receiving unit is capable of determining a degree of directionality of the light the device is exposed to, and in particular, of determining if the device is exposed to hard light or to soft light.

In a preferred embodiment of the arrangement, the device comprises means for determining UV-radiation and is adapted for also transmitting data representing or derived from the determination of UV-radiation to the re ceiving unit, and the receiving unit is capable of recei ving said data representing or derived from the determin ation of UV-radiation and is capable of determining, ba sed on said data, if the device is exposed to sunlight or to artificial light.

In a further preferred embodiment of the ar rangement, the device comprises at least one temperature sensor for determining the ambient temperature near the photosensitive elements and is adapted for also transmit ting data representing or derived from the determination of the ambient temperature near the photosensitive elements to the receiving unit, and the receiving unit is capable of receiving said data representing or derived from the determination of the ambient temperature near the photosensitive elements. In still a further preferred embodiment of the arrangement, the receiving unit is capable of deter mining, from the received data representing or derived from the photo signals or power yields of the individual photosensitive elements, the variations of the photo signals or power yields of the individual photosensitive elements over time.

Preferably, the receiving unit is capable to determine from said variations if the supporting structure the photosensitive elements are arranged at is in motion or is stationary. This can be accomplished in accordance with the before mentioned preferred embodiments of the invention, in which, if the individual photo sig nals or power yields of the individual photosensitive elements considerably vary within short periods (e.g. within seconds) , it is determined that the person or object is in motion. If there are no variations or only small ones within short time periods, it is determined that the person or object is stationary.

In yet a further preferred embodiment of the arrangement, the receiving unit is capable of determining its own local position and/or the local position of the device, is capable of choosing, based on. said local po sition, an external data source which provides UV-radia- tion data and/or ambient temperature data for the region of said local position.

In case the external data source provides UV- radiation data, it is further preferred that the recei ving unit is capable of estimating, based on the deter mined lighting situation and the UV-radiation data pro vided by said data source, the quantity of UV-radiation the device is exposed to and/or has been exposed to over a certain span of time. Such arrangements are especially suitable for monitoring the UV-radiation a person is ex posed to or has been exposed to.

In that case it is also preferred that the receiving unit is part of a system for supporting a per- son using a sunscreen product in determining the point in time for the next application of the product or the in terval until the next application of the product, and that the receiving unit is adapted to calculate the point in time and/or the interval based on an algorithm taking into account the variations of the photo signals or power yields of the individual photosensitive elements over time and/or the determined ambient temperature near the photosensitive elements and the ambient temperature data for the region of said local position received from the data source.

By advantage, the algorithm is designed in such a way that in case the variations of the photo sig nals or power yields of the individual photosensitive elements over time exceed a certain threshold value (e.g. more than 30% within some seconds), the remaining time until the next application of the product is reduced, in particular increasingly reduced with increasing varia tions .

Further by advantage, the algorithm is de signed in such a way that in case the determined ambient temperature near the photosensitive elements exceeds or underruns the ambient temperature for the region of said local position received from the external data source for a certain time (e.g. some minutes) and to a certain ex tent (e.g. more than 5°C), the remaining time until the next application of the product is reduced.

In case the receiving unit is part of a sys tem for supporting a person using a sunscreen product in determining the point in time for the next application of the product or the interval until the next application of the product, it is preferred that the receiving unit is capable of visually and/or acoustically indicating to the person the point in time for the next application of the product or the interval until the next application of the product. This can e.g. be done by indicating on a display a time bar or a countdown in hours/minutes of the time that remains until the next recommended application of the sunscreen product and by emitting an acoustic signal upon expiration of that time.

If the receiving unit is a mobile phone, pre ferably a smart phone with an App adapted to make at least the most important determined information recogni zable to a user, like e.g. the quantity of UV-radiation the device is exposed to or has been exposed to since a certain point in time, respectively and/or the recom mended remaining time until the next application of the sunscreen product, such information can be provided to a user in quite convenient and inconspicuous manner.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood and objects other than those set forth above will become ap parent when consideration is given to the following de tailed description thereof. Such description makes reference to the annexed drawings, wherein:

Fig. 1 is a perspective view onto a first device according to the invention;

the Figures 2a to 6a are schematic represen tations in different lighting situations of a first arrangement according to the invention which includes the device of Fig. 1;

the Figures 2b to 6b show the information de picted on the display of the smart phone of the arrange ment in the respective lighting situations of the Figures 2a to 6a;

Fig. 7 is a perspective view onto a second device according to the invention;

the Figures 8a to 12a are schematic represen tations in different lighting situations of a second arrangement according to the invention which includes the device of Fig. 7; the Figures 8b to 12b show the information depicted on the display of the smart phone of the arrangement in the respective lighting situations of the Figures 8a to 12a;

Fig. 13 is a perspective view onto a third device according to the invention;

the Figures 14a to 18a are schematic repre sentations in different lighting situations of a third arrangement according to the invention which includes the device of Fig. 7;

the Figures 14b to 18b show the information depicted on the display of the smart phone of the ar rangement in the respective lighting situations of the Figures 14a to 18a;

Fig. 19 is a flow chart of the method of determining the lighting situation and the UV-exposure employed in the first arrangement shown in the Figures 2a to 6a;

Fig. 20 is a flow chart of the method of determining the lighting situation and the UV-exposure employed in the second arrangement shown in the Figures 8a to 12a; and

the Figures 21a and 21b in combination with each other show a flow chart of the method of determining the lighting situation, the UV-exposure and the interval until the next application of a sunscreen product employ ed in the third arrangement shown in the Figures 14a to 18a.

MODES FOR CARRYING OUT THE INVENTION

Fig. 1 shows a perspective view onto a first device 1 according to the invention.

The device 1 is embodied as a button, which can be attached to the clothing of a person. Its top side has the shape of a frustum 2 of a flat pyramid with five equal sides. The central surface of this frustum 2 is formed by a UV-sensor 3 of the gallium arsenide type, the surrounding surfaces of the five pyramid sides are formed by identical silicon based photovoltaic cells 4. These photovoltaic cells 4 are sensitive to visible light and to UV-radiation . The maximum power yield in directional light is achieved with these cells 4 when the light per pendicularly impacts onto the light absorbing surface of the photovoltaic cell (optimum angle of impact of the light onto the light absorbing surface of the photovol taic cell according to the claims), and the power yield decreases with a deviation from said optimum angle of impact .

The photovoltaic cells 4 and the UV-sensor 3 are arranged on a supporting structure 5 carrying them in such a manner that the five photovoltaic cells 4 require different directions of directional light in order to be hit by the light in their respective optimum angle of im pact of light. In other words, the cells 4 are arranged in such a way relative to each other on the supporting structure 5 that with directed light it is not possible to hit more than one of them in the optimum angle of impact of light, i.e. perpendicular onto their surfaces.

As is indicated in Fig. 1 in dashed lines, inside the device 1 there is arranged an energy storage 6 in the form of a capacitor 6 and a transmitting unit 7 with an electronic circuitry (not shown) , by means of which data representing or derived from the power yields of the individual photovoltaic cells 4 and from the UV- sensor 3 can be transmitted by Bluetooth to a receiving unit, e.g. to a mobile phone.

The capacitor 6 is charged by the cells 4 and provides the electrical energy for the transmitting unit 7.

The Figures 2a to 6a are schematic represen tations of a first arrangement 8 according to the invention in different lighting situations. The Figures 2b to 6b show the information depicted on the display of the smart phone 9 of the arrangement 8 in the respective lighting situations according to the Figures 2a to 6a.

The arrangement 8 comprises the before described device 1 of Fig. 1 and a receiving unit 9 in the form of smart phone 9, which is capable of receiving the data transmitted by the device 1, of determining, based on said data, the actual lighting situation of the device 1 and of making recognizable the last-mentioned on its display. For doing so, the smart phone 9 is equipped with a specific App.

Fig. 19 is a flow chart of the method of de termining the lighting situation and the UV-exposure emp loyed in this first arrangement shown in the Figures 2a to 6a .

By means of the UV-sensor 3, a UVI (UV-index) measurement is performed and the UVI determined by the sensor UVIs is compared with a threshold value. If the determine value UVIs is bigger than the threshold value, this is taken as an indication that the device 1 is loca ted outdoors (sunlight) . If it is smaller, it is measured if the device is exposed to visible light, which is done by checking if the photovoltaic cells 4 produce any appreciable power yield. If so, this is taken as an indica tion that the device 1 is located indoors (artificial light) . If there is no appreciable power yield of the photovoltaic cells 4, this is taken as an indication that the device 1 is covered. In that case, an error message will occur on the smart phone 9.

In case it is found that the device 1 is lo cated outdoors, the power yields of the individual photo voltaic cells 4 are determined and compared with each other .

If it is found that the power yields of the cells significantly differ from each other, e.g. there is a scatter between the power yields of individual cells in which the level of the lowest power yield is less than 50% of the level of the highest power yield, this is taken as an indication that the device 1 is exposed to directional light.

If it is found that the power yields of the cells do not significantly differ from each other, e.g. there is a scatter between the power yields of individual cells in which the level of the lowest power yield is more than 50% of the level of the highest power yield, this is taken as an indication that the device 1 is ex posed to diffuse light.

The before described course of determining the lighting situation is continuously repeated.

In order to determine the amount of UV-radia- tion the device 1 is exposed to, an estimated UVI (UV- index) is calculated as follows:

If it is found that the device is exposed outdoors to diffuse light, the estimated UVI is identical to the UVIs determined by the UV-sensor 3.

If it is found that the device is exposed outdoors to directional light, the highest UVIs which has been determined by the UV-sensor 3 over a certain time period or number of measurements, respectively, is taken as estimated UVI, e.g. the highest UVIs determined by the UV-sensor 3 during the last 30 or 60 seconds.

The Figures 2a and 2b show the arrangement 8 with the device 1 exposed to artificial light AL genera ted by an electric light bulb 10. The device 1 transmits data 11 representing the actual power yields of the indi ^¬ vidual photovoltaic cells 4 and data 12 derived from the UV-sensor 3 to the smart phone 9. The smart phone 9, based on the data 11 representing the actual power yields of the individual photovoltaic cells 4, determines the light intensity and the degree of directionality of the light AL the device 1 is exposed to, and makes these in formation recognizable on the display in the form of a horizontal bar with a length between "0" and "max" for the light intensity and as an indicator mark on a hori ^¬ zontal line between "diffuse" (soft light) and "directed" (Hard light) for the degree of directionality. It furthermore shows the individual power yields of the photovoltaic cells 4 on top of the display as individual horizontal bars with a length between "0" and "max" and indicates the light situation with regard to the light source (artificial or sunlight) as an indicator mark on a horizontal line between a Bulb-Symbol (artificial light) and a Sun-Symbol (sunlight) .

Based on the data 12 derived from the UV-sen- sor 3, the smart phone 9 calculates the estimated UVI (UV-index) and indicates shows it at the bottom of the display .

As can be seen here, with the device exposed to artificial light AL of an electric bulb 10, the power yields of the photovoltaic cells 4 amount to about one third of the maximum possible power yield but quite con siderably differ from each other, which leads to a deter mined lighting situation having a moderate light inten sity and an elevated degree of directionality which is closer to hard light than to soft light.

Since the artificial light of the light bulb 10 practically does not contain UV-radiation, the indi cated UVI is almost zero (0.1) and the indicator mark on the horizontal line between the Bulb-Symbol (artificial light) and the Sun-Symbol (sunlight) clearly indicates artificial light.

The Figures 3a and 3b show the arrangement 8 with the device 1 directly exposed to sunlight SL under a blue sky and in motion. The device 1, as already des cribed before, transmits data 11 representing the actual power yields of the individual photovoltaic cells 4 and data 12 derived from the UV-sensor 3 to the smart phone 9, and the smart phone 9 performs the determinations and makes the results recognizable as described before.

As can be seen here, with the device 1 exposed to direct sunlight SL, the power yields of three of the five photovoltaic cells 4 amount to between 60% to 80% of the maximum possible power yield while the other two are in the range of 25% of the maximum possible power yield, thus, there is an extreme scatter between the po wer yields of individual cells 4. This power yield con stellation leads to a determined lighting situation ha- ving a very high light intensity and an extreme degree of directionality, i.e. very hard light.

Since the light of the sun 13 contains a con siderable amount of UV-radiation and the device 1 has been in motion during the last 30 seconds so that the UV- sensor 3 has been hit by the sunlight at least temporari ly under its optimum angle of impact giving the highest photo signal or power yield, respectively, the indicated UVI is quite high here (5.3) and the indicator mark on the horizontal line between the Bulb-Symbol (artificial light) and the Sun-Symbol (sunlight) clearly indicates sunlight .

The Figures 4a and 4b show the arrangement 8 with the device 1 exposed to sunlight SL under a sunshade 14 with the sun 13 shining from a blue sky and in motion. The device 1, as already described before, transmits data 11 representing the actual power yields of the individual photovoltaic cells 4 and data 12 derived from the UV-sen- sor 3 to the smart phone 9, which performs the determinations and makes the results recognizable as described before.

As can be seen here, with the device 1 exposed to sunlight SL from a blue sky under a sunshade 14, the power yields of the photovoltaic cells 4 amount to between 30% to 50% of the maximum possible power yield and considerably differ from each other, which leads to a determined lighting situation having a medium light in tensity and an elevated degree of directionality which is closer to hard light than to soft light.

The indicated UVI here still is high (3.0) and the indicator mark on the horizontal line between the Bulb-Symbol (artificial light) and the Sun-Symbol (sun light) clearly indicates sunlight.

The Figures 5a and 5b show the arrangement 8 with the device 1 exposed to sunlight SL under a cloudy sky. The device 1, as already described before, transmits data 11 representing the actual power yields of the indi vidual photovoltaic cells 4 and data 12 derived from the UV-sensor 3 to the smart phone 9, and the smart phone 9 performs the determinations and makes the results reco gnizable as described before.

As can be seen here, with the device 1 expo sed to sunlight SL under a sky full of clouds 15, the power yields of the five photovoltaic cells 4 are comple tely equal and amount to about 70% of the maximum possi ble power yield. Thus, there is practically no scatter between the power yields of the individual cells 4. This power yield constellation leads to a determined lighting situation having a very high light intensity and low de gree of directionality, i.e. quite soft light.

The indicated UVI is quite high here (5.0) and the indicator mark on the horizontal line between the Bulb-Symbol (artificial light) and the Sun-Symbol (sunlight) clearly indicates sunlight.

The Figures 6a and 6b show the arrangement 8 with the device 1 exposed to sunlight SL under a sunshade 14 at a cloudy sky. The device 1, as already described before, transmits data 11 representing the actual power yields of the individual photovoltaic cells 4 and data 12 derived from the UV-sensor 3 to the smart phone 9, and the smart phone 9 performs the determinations and makes the results recognizable as described before.

As can be seen here, with the device 1 exposed to sunlight SL under a sunshade 14 and with a sky full of clouds 15, the power yields of the five photo ^¬ voltaic cells 4 are quite equal and amount to about 40% of the maximum possible power yield. Thus, there is only little scatter between the power yields of individual cells 4. This power yield constellation leads to a determined lighting situation having a medium light intensity and low degree of directionality, i.e. quite soft light.

The indicated UVI is medium here (2.7) and the indicator mark on the horizontal line between the Bulb-Symbol (artificial light) and the Sun-Symbol (sun light) clearly indicates sunlight.

Fig. 7 shows a perspective view onto a second device 1 according to the invention.

This device 1 differs from the device of Fig. 1 merely in that the central surface at the top side of the device is formed by two photovoltaic cells 16a, 16b of identical type and shape, which are sensitive to visi ble light and to UV-radiation .

The first one 16a of these two photovoltaic cells 16a, 16b is coated with PTFE, which has a high transmittance in the whole spectrum, i.e. for UV-radia- tion and for visible light.

The second one 16b of these two photovoltaic cells 16a, 16b is coated with acrylic PMMA, which has a high transmittance for visible light and no transmittance for UV-radiation .

Thus, if these two cells 16a, 16b are exposed to artificial light from an electric light bulb which practically does not contain UV-radiation, they will show identical power yields. If they are exposed to sunlight which contains UV-radiation, the power yield of the first cell 16a will be higher than the one of the second cell 16b which is blocked from the UV-radiation. Thus, by sim ply comparing the power yields of the photovoltaic cells 16a, 16b, it can be decided if the device 1 is exposed to artificial light (indoor) or sunlight (outdoor) . However, since the possible differences in the power yields of the photovoltaic cells 16a, 16b are quite small, a quantita ^¬ tive determination of the amount of UV-radiation the device 1 is exposed to is not possible here. The Figures 8a to 12a are schematic representations of a second arrangement 17 according to the in vention in different lighting situations. The Figures 8b to 12b show the information depicted on the display of the smart phone of the arrangement in the respective lighting situations of the Figures 8a to 12a.

The arrangement 17 comprises the before des cribed second device 1 of Fig. 7 and, as the first arrangement 8, a receiving unit 9 in the form of smart phone 9, which is capable of receiving the data transmitted by the device 1, of determining, based on said data, the actual lighting situation of the device 1 and of making recognizable the latter on its display. For doing so, the smart phone 9 is equipped with a specific App .

Fig. 20 is a flow chart of the method of determining the lighting situation and the UV-exposure employed in this second arrangement shown in the Figures 8a to 12a.

By means of the two photovoltaic cells 16a, 16b it is determined, if UV-radiation is present or not.

If it is determined that UV-radiation is pre sent, this is taken as an indication that the device 1 is located outdoors (sunlight). If it is determined that no UV-radiation is present, it is measured if the device is exposed to visible light, which is done by checking if the photovoltaic cells 4 produce any appreciable power yield. If so, this is taken as an indication that the device 1 is located indoors (artificial light) . If there is no appreciable power yield of the photovoltaic cells 4, this is taken as an indication that the device 1 is covered. In that case, an error message will occur on the smart phone 9.

In case it is found that the device 1 is lo ^¬ cated outdoors, the power yields of the individual photo ^¬ voltaic cells 4 are determined and compared with each other . If it is found that the power yields of the cells significantly differ from each other, e.g. there is a scatter between the power yields of individual cells in which the level of the lowest power yield is less than 50% of the level of the highest power yield, this is taken as an indication that the device 1 is exposed to directional light.

If it is found that the power yields of the cells do not significantly differ from each other, e.g. there is a scatter between the power yields of individual cells in which the level of the lowest power yield is more than 50% of the level of the highest power yield, this is taken as an indication that the device 1 is exposed to diffuse light.

In addition, the highest power yield, i.e. the power yield of the cell 4 which is providing the highest power yield of all cells 4, is determined and compared with a threshold value, e.g. 50% of the maximum possible power yield of the cells.

If it is found that the highest power yield is below the threshold value, this is taken as an indication that the device 1 is exposed to the light in the shado .

If it is found that the highest power yield is above the threshold value, this is taken as an indi cation that the device 1 is directly exposed to the light .

Furthermore, the location of the arrangement is determined, e.g. by GPS-antennas of the smart phone 9, and based on that local position, an external data source 19 is evaluated and contacted, which provides UV-radia- tion data 20, i.e. an UVI-value termed UVIw for the region of said local position.

In order to determine the amount of UV-radia- tion the device 1 is exposed to, an estimated UVI (UV-in- dex) is calculated as follows: If it is found that no UV-radiation is present, the estimated UVI is zero (0.0) .

If it is found that UV-radiation is present and thus the device is outdoors and is directly exposed to directional light or diffuse light, the estimated UVI is equal to the UVIw provided by the external data source .

If it is found that UV-radiation is present and thus the device is outdoors but is in the shadow exposed to directional light, the estimated UVI is the UVIw provided by the external data source multiplied by a factor fsl smaller than 1.0 which is a function of the highest power yield of the cells 4, i.e. the power yield of the cell 4 which is providing the highest power yield of all cells 4. This factor can for example be the quo- tient of the highest power yield of the cells 4 and the maximum possible power yield of the cells 4.

If it is found that UV-radiation is present and thus the device is outdoors but is in the shadow exposed to diffuse light, the estimated UVI is the UVIw provided by the external data source multiplied by a factor fs2 smaller than 1.0 which is a function of the highest power yield of the cells 4, i.e. the power yield of the cell 4 which is providing the highest power yield of all cells 4 or of the average power yield of the cells 4. This factor can for example be the quotient of the highest power yield or the average power yield, respec tively, of the cells 4 and the maximum possible power yield of the cells 4.

The Figures 8a and 8b show the arrangement 17 with the device 1 exposed to artificial light AL genera ted by an electric light bulb 10. The device 1 transmits data 11 representing the actual power yields of the five photovoltaic cells 4 forming the surfaces of the sides of the frustum shape 2 of the top side of the device 1 and data 12 representing the actual power yields of the two photovoltaic cells 16a, 17b forming the central surface of the frustum shape 2 of the top side of the device 1 to the smart phone 9.

The smart phone 9, based on the data 11 representing the actual power yields of the individual photovoltaic cells 4 forming the surfaces of the sides of the frustum shape 2, determines the light intensity and the degree of directionality of the light AL the device 1 is exposed to, and makes these information recognizable on the display in the form of a horizontal bar with a length between "0" and "max" for the light intensity and as an indicator mark on a horizontal line between

"diffuse" (soft light) and "directed" (Hard light) for the degree of directionality. It furthermore shows the individual power yields of the photovoltaic cells 4 on top of the display as individual horizontal bars with a length between "0" and "max".

As can be seen here, with the device exposed to artificial light AL of an electric bulb 10, the power yields of the photovoltaic cells 4 amount to about one third of the maximum possible power yield but quite considerably differ from each other, which leads to a determined lighting situation having a moderate light intensity and an elevated degree of directionality which is closer to hard light than to soft light.

Furthermore, based on the data 12 represen ting the actual power yields of the two photovoltaic cells 16a, 17b forming the central surface of the frustum shape 2, the smart phone 9 decides about the lighting situation with regard to the light source (artificial or sunlight) the device 1 is exposed to, and makes it reco gnizable by either showing a Bulb-Symbol (artificial light) or a Sun-Symbol (sunlight) .

If, as in the situation depicted here, there is no significant difference in the power yields of the two photovoltaic cells 16a, 16b since the artificial light of the light bulb 10 practically does not contain any UV-radiation, it shows the Bulb-Symbol and at the bottom of the display indicates an estimated UVI-value of

0.

The Figures 9a and 9b show the arrangement 17 with the device 1 directly exposed to sunlight SL under a blue sky. The device 1, as already described before, transmits data 11 representing the actual power yields of the five photovoltaic cells 4 forming the surfaces of the sides of the frustum shape 2 and data 12 representing the actual power yields of the two photovoltaic cells 16a,

17b forming the central surface of the frustum shape 2 to the smart phone 9, and the smart phone 9 performs the de terminations and makes the results recognizable as des cribed before.

As can be seen here, with the device 1 expo sed to direct sunshine SL, the power yields of three of the five photovoltaic cells 4 amount to between 60% to 80% of the maximum possible power yield while the other two are in the range of 25% of the maximum possible power yield, thus, there is an extreme scatter between the power yields of individual cells 4. This power yield con stellation leads to a determined lighting situation ha ving a very high light intensity and an extreme degree of directionality, i.e. very hard light.

Since the light of the sun 13 contains a considerable amount of UV-radiation, there is a significant difference in the power yields of the two photovoltaic cells 16a, 16b, and thus the smart phone 9 shows the Sun- Symbol .

However, as mentioned earlier, based on the information 12 received from the device 1, the smart pho ne 9 is not in position to reliably quantify the amount of UV-radiation the device 1 is exposed to.

In order to do so, in cases where the smart phone 9 from the power yields of the two photovoltaic cells 16a, 16b derives that there is UV-radiation present and thus the device 1 is exposed to sunlight, it determines its local position, e.g. by GPS, and based on that local position, evaluates and contacts 18 an external data source 19, in this case a weather station 19 access ible via internet, which provides UV-radiation data 20 for the region of said local position.

Based on the lighting situation determined from the data 11 representing the actual power yields of the five photovoltaic cells 4 forming the surfaces of the sides of the frustum shape 2 and the UV-radiation data provided by the weather station 19, the smart phone esti mates the quantity of UV-radiation the device 1 is exposed to and shows said quantity in the form of an estimated UVI-value at the bottom of its display. Furthermore, above that estimated value, it indicates the UVI-value which has been provided by the weather station 19 for the region .

In the situation depicted in the Figures 9a and 9b, the UVI-value provided by the weather station is 5.3. Since according to the determined lighting situation the device 1 is directly exposed to the sunshine (very high light intensity, very high degree of directionali ty) , the UVI-value estimated by the smart phone 9 is identical to the value provided by the weather station 19.

The Figures 10a and 10b show the arrangement 17 with the device 1 exposed to sunlight SL under a sun shade 14 with the sun 13 shining from a blue sky. The device 1, as already described before, transmits data 11 representing the actual power yields of the five photovoltaic cells 4 forming surfaces of the sides of the frustum shape 2 and data 12 representing the actual power yields of the two photovoltaic cells 16a, 17b forming the central surface of the frustum shape 2 to the smart phone 9, which performs the determinations and makes the results recognizable as described before.

As can be seen here, with the device 1 expo sed to sunlight SL from a blue sky under a sunshade 14, the power yields of the photovoltaic cells 4 amount to between 30% to 50% of the maximum possible power yield and considerably differ from each other, which leads to a determined lighting situation having a medium light intensity and an elevated degree of directionality which is closer to hard light than to soft light.

Since the light the device 1 is exposed to contains a considerable amount of UV-radiation, there is a significant difference in the power yields of the two photovoltaic cells 16a, 16b, and thus the smart phone 9 shows the Sun-Symbol and performs the already before des- cribed steps in order to get the UV-radiation value for the region from the weather station 19 and to estimate the UV-radiation the device 1 is exposed to. Since here the weather is identical as in the situation of Fig. 9 (sunshine from blue sky), the UVI-value provided by the weather station again is 5.3 here.

The UVI-value estimated by the smart phone 9 for the exposition of the device 1 however differs, since according to the determined lighting situation the device 1 is not directly exposed to the sunlight SL, but is in the shadow (high degree of directionality but medium light intensity) . For this case, the smart phone 9 calcu lates from the UVI-value received from the weather sta tion 19 by taking into account the reduced light intensi ty an estimated UVI-value of 3.0 for the UV-exposure of the device 1.

The Figures 11a and lib show the arrangement 17 with the device 1 exposed to sunlight SL under a cloudy sky. The device 1, as already described before, trans mits data 11 representing the actual power yields of the five photovoltaic cells 4 forming surfaces of the sides of the frustum shape 2 and data 12 representing the actu al power yields of the two photovoltaic cells 16a, 16b forming the central surface of the frustum shape 2 to the smart phone 9, and the smart phone 9 performs the deter- minations and makes the results recognizable as described before . As can be seen here, with the device 1 expo sed to sunlight SL under a sky full of clouds 15, the power yields of the five photovoltaic cells 4 are completely equal and amount to about 70% of the maximum possible power yield. Thus, there is practically no scatter between the power yields of the individual cells 4. This power yield constellation leads to a determined lighting situation having a very high light intensity and low de gree of directionality, i.e. quite soft light.

Since the light SL the device 1 is exposed to contains a considerable amount of UV-radiation, there is a significant difference in the power yields of the two photovoltaic cells 16a, 16b, and thus the smart phone 9 shows the Sun-Symbol and performs the already before described steps in order to get the UV-radiation value for the region from the weather station 19 and to estimate the UV-radiation the device 1 is exposed to.

In the situation depicted in the Figures 11a and lib, the UVI-value provided by the weather station again is 5.3. Since according to the determined lighting situation the device 1 is directly exposed to the sunlight SL under a cloudy sky (very high light intensity, low degree of directionality) , the UVI-value estimated by the smart phone 9 here is identical to the value provided by the weather station 19, namely 5.3.

The Figures 12a and 12b show the arrangement 17 with the device 1 exposed to sunlight SL under a sun shade 14 at a cloudy sky. The device 1, as already described before, transmits data 11 representing the actual power yields of the five photovoltaic cells 4 forming the surfaces of the sides of the frustum shape 2 and data 12 representing the actual power yields of the two photovoltaic cells 16a, 17b forming the central surface of the frustum shape 2 to the smart phone 9, and the smart phone 9 performs the determinations and makes the results recognizable as described before. As can be seen here, with the device 1 expo sed to sunlight SL under a sunshade 14 and with a sky full of clouds 15, the power yields of the five photovoltaic cells 4 are quite equal and amount to about 40% of the maximum possible power yield. Thus, there is only little scatter between the power yields of the individual cells 4. This power yield constellation leads to a deter mined lighting situation having a medium light intensity and low degree of directionality, i.e. quite soft light.

Since the light SL the device 1 is exposed to contains a considerable amount of UV-radiation, there is a significant difference in the power yields of the two photovoltaic cells 16a, 16b, and thus the smart phone 9 shows the Sun-Symbol and performs the already before des cribed steps in order to get the UV-radiation value for the region from the weather station 19 and to estimate the UV-radiation the device 1 is exposed to.

Since here the weather is identical as in the situation of the Figures 11a and lib (sunlight from cloudy sky) , the UVI-value provided by the weather station 19 again is 5.3 here.

The UVI-value estimated by the smart phone 9 for the exposition of the device 1 however differs, since according to the determined lighting situation the device 1 is not directly exposed to the sunlight SL under a cloudy sky but is in the shadow (medium light intensity, low degree of directionality) . For this case, the smart phone 9 from the UVI-value received from the weather station 19 by taking into account the reduced light inten sity estimates an UVI-value of 2.7 for the UV-exposure of the device 1.

Fig. 13 shows a perspective view onto a third device 1 according to the invention.

This device 1 differs from the device of Fig.

7 merely in that in the center of the central surface at the top side of the device, which is formed by the two photovoltaic cells 16a, 16b that are sensitive to visible light and to UV-radiation, there is arranged a temperature sensor 21 for determining the ambient temperature near the photovoltaic cells 4, 16a, 16b. Furthermore, the transmitting unit 7 of the device 1 is adapted for also transmitting data representing or derived from the deter- mination of the ambient temperature near the photovoltaic cells 4, 16a, 16b to a receiving unit.

The Figures 14a to 18a are schematic representations of a third arrangement 17 according to the in vention in different lighting situations. The Figures 14b to 18b show the Information depicted on the display of the smart phone of the arrangement in the respective lighting situations of the Figures 14a to 18a.

The arrangement 17 according to the Figures 14a to 18a, with regard to the determination of the lighting situation and the way of making it recognizable, is identical to the arrangement according to the Figures 8a to 12a, so that it is not necessary to repeat here the description thereof.

It differs, however, from the arrangement according to the Figures 8a to 12a in that it comprises the before described third device 1 of Fig. 13 having a temperature sensor 21, and in that its receiving unit 9 is part of a system for supporting a person using a sunscreen product in determining the interval until the next application of the product is due.

For this, the receiving unit 9 is adapted to calculate the interval based on an algorithm taking into account the determined lighting situation, variations of the power yields of the individual photovoltaic cells 4 over time, the ambient temperature near the photovoltaic cells 4 determined by the temperature sensor 21 of the device 1, ambient temperature data 22 for the region of said local position received from an external data source 19 and particular parameters of the applied sunscreen product, like e.g. the design protection duration of said product, which may be already part of the algorithm or may be entered into it based on the chosen product by the user. The receiving unit 9 indicates the calculated in terval or the remaining time in hours and minutes until the next recommended application, respectively, on the display (see e.g. "Next Application in: 1:50" in Fig.

15b) , and upon expiration of that interval emits an acoustic signal. For doing so, the smart phone 9 is equipped with a specific App.

Figures 21a and 21b show a flow chart of the method of determining the lighting situation, the UV- exposure and the interval until the next application of a sunscreen product employed in the third arrangement shown in the Figures 14a to 18a.

By means of the two photovoltaic cells 16a, 16b it is determined, if UV-radiation is present or not.

If it is determine that UV-radiation is pre sent, this is taken as an indication that the device 1 is located outdoors (sunlight) . If it is determined that no UV-radiation is present, it is measured if the device is exposed to visible light, which is done by checking if the photovoltaic cells 4 produce any appreciable power yield. If so, this is taken as an indication that the device 1 is located indoors (artificial light) . If there is no appreciable power yield of the photovoltaic cells 4, this is taken as an indication that the device 1 is covered. In that case, an error message will occur on the smart phone 9.

In case it is found that the device 1 is lo cated outdoors, the power yields of the individual photo voltaic cells 4 are determined repeatedly over a certain period of time, e.g. 30 seconds, and it is evaluated if the determined power yields per cell do significantly vary over time, e.g. more than 30% within some seconds.

If that is the case, this is taken as an indication that the device is in motion. If there are no variations or only small ones within short time periods, it is assumed that the device 1 is stationary. Furthermore, the power yields of the individual photovoltaic cells 4 are compared with each other.

If it is found that the power yields of the individual cells 4 significantly differ from each other, e.g. there is a scatter between the power yields of dif ferent cells 4 in which the level of the lowest power yield is less than 50% of the level of the highest power yield, this is taken as an indication that the device 1 is exposed to directional light.

If it is found that the power yields of the cells do not significantly differ from each other, e.g. there is a scatter between the power yields of individual cells in which the level of the lowest power yield is more than 50% of the level of the highest power yield, this is taken as an indication that the device 1 is ex posed to diffuse light.

In addition, the highest power yield, i.e. the power yield of the cell 4 which is providing the highest power yield of all cells 4, is determined and compared with a threshold value, e.g. 50% of the maximum possible power yield of the cells.

If it is found that the highest power yield is below the threshold value, this is taken as an indi cation that the device 1 is exposed to the light in the shado .

If it is found that the highest power yield is above the threshold value, this is taken as an indi cation that the device 1 is directly exposed to the light .

Also, the temperature Ts near the photovol taic cells 4, 16a, 16b is determined by means of the tem perature sensor 21.

Furthermore, the location of the arrangement 17 is determined, e.g. by GPS-antennas of the smart phone 9, and based on that local position, an external data source 19 is evaluated and contacted, which provides UV- radiation data 20, i.e. an UVI-value (also termed UVIw) and ambient temperature data 22 termed Tw for the region of said local position.

The ambient temperature Ts determined with the sensor 21 und the ambient temperature Tw provided by the weather station 19 are compared, and if the deter mined temperature Ts exceeds the temperature Tw provided by the weather station 19 by a certain threshold value (threshold value 2), e.g. by 5°C, this is taken as an indication that the device 1 is directly exposed to sun light from blue sky.

If not, it is evaluated if the determined temperature Ts undershoots the temperature Tw provided by the weather station 19 by a certain threshold value

(threshold value 3), e.g. by 5°C. If yes, this is taken as an indication that the device 1 is or shortly before has been immersed in water.

In order to determine the amount of UV-radia- tion the device 1 is exposed to, an estimated UVI (UV- index) is calculated in the same way as explained before with reference to the second arrangement 17 according to the Figures 8a to 12a. Thus, it is not again explained here but is referred to the before mentioned description.

In order to determine when the next appli cation of a sunscreen product is due, following deter minations are made:

The time interval Ata between two applica tions of a specific sunscreen product is calculate by taking the design protection duration td (sunscreen duration) of said product given by the manufacturer of the product, e.g. 5 hours and reducing it with certain factors taking account of the individual application situation, like e.g. water contact fw (water factor) and sweating/friction with clothing due to physical activity fpa (transpiration/friction factor) . As formula, this could read as follows:

Ata = td {1 - fw - fpa) For example, in case the before described evaluations lead to the indication that the device is or has been in water, the applied water factor fw is 0.5, else it is 0.0.

Also for example, in case the before descri bed evaluations lead to the indication that the device was in motion for more than 5 minutes and the ambient temperature tw obtained from the external weather station is above 25°C, the applied transpiration/friction factor fpa is 0.33. If in addition it is found that the device was directly exposed to sunlight from blue sky for that time, the applied transpiration/friction factor fpa is 0.5. Else it is 0.0.

The time period left until the next applica- tion of the sunscreen product is due, which is indicated on the mobile phone 9, is calculated by deducting from the determined time interval Ata the time which has elap sed already since the last application of the sunscreen product .

The Figures 14a and 14b show the arrangement

17 with the device 1 exposed to artificial light AL generated by an electric light bulb 10. For the deter mination and indication on the display of the lighting situation, reference is made to the description of the Figures 8a and 8b.

The device 1 transmits, in addition to the data 11 representing the actual power yields of the pho tovoltaic cells 4 and the data 12 representing the actual power yields of the two photovoltaic cells 16a, 17b, data 23 representing the ambient temperature near the photovoltaic cells 4, 16a, 16b to the smart phone 9.

Since practically no UV-radiation is present, the algorithm for the calculation of the interval until the next application of the sunscreen product calculates the maximum interval given by the parameters of the pro ^¬ duct, which in the present case in 5 hours ("5:00") . This interval in all examples is counted-down on the display as time expires.

The Figures 15a and 15b show the arrangement 17 with the device 1 directly exposed to sunlight SL under a blue sky. 40 minutes have elapsed already since the last application of the sunscreen product, and the device has been in motion for 15 minutes during that time. The ambient temperature Tw provided by the external data source 19 is 27°C. For the determination and indication on the display of the lighting situation, referen- ce is made to the description of the Figures 9a and 9b.

Since the light of the sun 13 contains a con siderable amount of UV-radiation, there is a significant difference in the power yields of the two photovoltaic cells 16a, 16b, and thus the smart phone 9 shows the Sun- Symbol.

However, as mentioned earlier, based on the information 12 received from the device 1, the smart pho ne 9 is not in position to reliably quantify the amount of UV-radiation the device 1 is exposed to.

In order to do so, in cases where the smart phone 9 from the power yields of the two photovoltaic cells 16a, 16b derives that there is UV-radiation present and thus the device 1 is exposed to sunlight, it deter mines its local position, e.g. by GPS, and based on that local position, evaluates and contacts 18 an external data source 19, in this case a weather station 19 accessible via internet, which provides UV-radiation data 20 and in addition also ambient temperature data 22 for the region of said local position.

In the situation depicted in the Figures 15a and 15b, the UVI-value provided by the weather station is 5.3. Since according to the determined lighting situation the device 1 is directly exposed to the sunshine (very high light intensity, very high degree of directionali ty) , the UVI-value estimated by the smart phone 9 is identical to the value provided by the weather station 19.

Furthermore, the receiving unit 9 compares the determined ambient temperature near the photovoltaic cells 4, 16a, 16b with the ambient temperature data 22 provided by the weather station 19, which in the situa tions depicted in the Figure 14b to 18b are identified to be equal .

Since 40 minutes have elapsed already since the last application of the sunscreen product, it was determined that the device 1 has been in motion for more than 5 minutes, the ambient temperature Tw provided by the external data source 19 is above 25°C and it is found that the device 1 during that time has been directly ex posed to sunlight from blue sky, the algorithm for the calculation of the interval until the next application of the sunscreen product calculates a shortened interval until the next application of the sunscreen product of 1 hour and 50 minutes ("1:50") .

The Figures 16a and 16b show the arrangement 17 with the device 1 exposed to sunlight SL under a sunshade 14 with the sun 13 shining from a blue sky. 2 hours have elapsed already since the last application of the sunscreen product and the device 1 has been more or less static during that time period. For the determination and indication on the display of the lighting situation, re ference is made to the description of the Figures 10a and 10b.

As can be seen, the estimated UVI-value for the UV-exposure is 3.0 here.

Since 2 hours have elapsed already since the last application of the sunscreen product but the device 1 has not significantly been in motion during that time, the algorithm for the calculation of the interval until the next application of the sunscreen product calculates an interval until the next application of the sunscreen product of 3 hours ("3:00") . The Figures 17a and 17b show the arrangement 17 with the device 1 exposed to sunlight SL under a clou dy sky. 30 minutes have elapsed already since the last application of the sunscreen product and it was determined that the device 1 has been in contact with water during that time period. For the determination and indi cation on the display of the lighting situation, reference is made to the description of the Figures 11a and 11b.

As can be seen, the estimated UVI-value for the UV-exposure is 5.3 here.

Since 30 minutes have elapsed already since the last application of the sunscreen product and it was determined that the device 1 has been in contact with water during that time period, the algorithm for the calculation of the interval until the next application of the sunscreen product calculates a shortened interval un til the next application of the sunscreen product of 2 hours ("2:00") .

The Figures 18a and 18b show the arrangement 17 with the device 1 exposed to sunlight SL under a sun shade 14 at a cloudy sky. 20 minutes have elapsed already since the last application of the sunscreen product and it was determined that the device 1 has been in motion during that time period. The ambient temperature Tw pro vided by the external data source 19 is 30°C. For the de termination and indication on the display of the lighting situation, reference is made to the description of the Figures 12a and 12b.

As can be seen, the estimated UVI-value for the UV-exposure is 2.7 here.

Since 20 minutes have elapsed already since the last application of the sunscreen product, it was determined that the device 1 has been in motion for more than 5 minutes and the ambient temperature Tw provided by the external data source 19 is higher than 25°C, the algorithm for the calculation of the interval until the next application of the sunscreen product calculates an interval until the next application of the sunscreen product of 3 hours ("3:00") .

After the user has applied the sunscreen product, he resets the calculation and receives a new interval until the next application from the mobile phone 9, which again counts downs while time elapses.

Although it is presently shown and described preferred embodiments of the invention, it has to be distinctly understood that the invention is not limited thereto but it may be instead variously embodied and practiced within the scope of the following claims.