FIELD OF THE INVENTION

The invention relates to a system for controlling one or more light sources to render UV light.

The invention further relates to a method of controlling one or more light sources to render UV light.

The invention also relates to a computer program product enabling a computer system to perform such a method.

BACKGROUND OF THE INVENTION

The vitamin D3 hormone is a very important molecule that is produced in the skin with the help of UV-B light. It is a very versatile bio active molecule that impacts a very large number of genes in the human genome, and hence a large number of tissues and cells. Vitamin D3 insufficiency is increasingly linked to reduced health and wellbeing. There is a global epidemic (up to 90%) in Vitamin D3 insufficiency, linked to a western lifestyle.

Hormonal supplements and food fortification are possible routes to improve vitamin D3 levels, but it has been shown that both have its limitations, in effectiveness and safety, compared to the natural process through outdoor cutaneous UV-B exposure. Natural sun exposure also has its large limitations, mainly due to large seasonal variations away from the equator, indoor lifestyle and the risk of sunburn and skin cancer. A supplementation using artificial UV-B light has benefits over alternative solutions. The UV-B light can be rendered by a general illuminating device rendering white light such as the one disclosed in WO2016202736A1 or by a dedicated UV device, e.g. a therapy device.

Although the amount of UV-B needed to increase vitamin D levels in living animals and humans is very little and not considered dangerous, individuals can respond differently to the exposure of skin to UV. The risk of skin cancer (melanoma) for instance is linked to excessive cumulative sun exposure. Although excessive UV exposure can lead to DNA damage and possibly skin cancer, vitamin D itself is linked to a reduction of the probability of skin cancer (melanoma). SUMMARY OF THE INVENTION

It is a first object of the invention to provide a system, which helps reduce the negative effects of artificial UV irradiation on the health of a person.

It is a second object of the invention to provide a method, which helps reduce the negative effects of artificial UV irradiation on the health of a person.

In a first aspect of the invention, a system for controlling one or more light sources to render UV light comprises at least one control interface and at least one processor configured to determine whether a current time of day falls in a period of the day which is associated with daylight and control, via said at least one control interface, said one or more light sources to render light simultaneously comprising a UV component and a cyan component in dependence on said current time of day falling in said period of the day and wherein the UV component is only rendered when the cyan component is also rendered.

The negative effects of artificial UV irradiation on the health of a person are reduced in two (linked) ways: a) the UV light is rendered during the photopic period, which corresponds to the daylight period at the person’s current geographical location if the person has not traveled recently, and not during the scotopic period (i.e. the period of the day that is not the photopic period); b) cyan light is rendered simultaneously with the UV light during the photopic period. Rendering UV light only during the photopic period and rendering cyan light simultaneously with the UV light decreases the risk of the UV light having negative effects on the health of the person. Said UV component preferably comprises at least an UV- B component. Said cyan component may comprise wavelengths in the range 470-520 nm.

Next to healthy levels of vitamin D (e.g. >30 ng/ml), timing of application of UV is also a very important, because skin cells themselves have an endogenous clock regulating the cellular circadian rhythmicity. Skin provides the first line of defense against many environmental and stress factors that exhibit dramatic diurnal variations such as solar ultraviolet (UV) radiation and temperature.

One study that linked the circadian clock to the control of UVB-induced DNA damage and skin cancers is the study of Sancar, which has been described in “Impact of the Circadian Clock on UV-Induced DNA Damage Response and Photocarcinogenesis “ by Dakup P et al. in Photochem Photobiol 2017, 93(1):296-303, and “A Control of skin cancer by the circadian rhythm” by Gaddameedhi S et al. in Proc Natl Acad Sci USA 2011,

108(46): 18790-18795. Sancar and coworkers showed that UV damage repair in mammals (nocturnal mouse) via the nucleotide excision repair (NER) pathway is regulated by a circadian rhythm. In parallel with the rhythmicity of the repair rate, they found that mice exposed to UV radiation at 4:00 AM display a decreased latency and about a fivefold increased multiplicity of skin cancer (invasive squamous cell carcinoma) than mice exposed to UVR at 4:00 PM for the same dose. They concluded that time of day matching the sleep/wake-rhythm of the mice is a contributing factor to its carcinogenicity in mice, and possibly in humans when exposed to of exposure to UVR.

Additionally, disruption of circadian rhythms (frequently happening with people with mental disorders, night shift workers and people who travel a lot, for example) is also often associated with an increased sensitivity to develop cancers, skin cancer being one of them.

Thus, UV light is good to stimulate cutaneous vitamin D production and can be protective against skin cancer as long as the exposure is below sunburn threshold levels, but the timing of exposure needs to be in the photopic period of the circadian phase. Light that enhances circadian entrainment is beneficial to reduce the risk for aging and carcinogenesis of the skin due to UV. Thus, by enhancing the ipRGC (i.e. intrinsically photosensitive Retinal Ganglion Cell; also referred to as melanopsin-containing Retinal Ganglion Cell or mRGC) activation during the day, the circadian rhythm is strengthened and a better protection against the harmful effects of UV irradiation is provided. Light with a cyan component is very effective for circadian entrainment.

While US2017/259079 A1 discloses a system that renders UV light or blue light in order to suppress melatonin production to help humans, animals and plants to regulate their circadian cycle after a disruption to their circadian cycle, i.e. for circadian entrainment, this system is not used for increasing a person’s vitamin D levels. US2017/259079 A1 does not disclose rendering light with both UV and blue components and it is not beneficial for the system disclosed in US2017/259079 A1 to do so.

Said at least one processor (5,35) is configured to control, via said at least one control interface (4,36), the light source (24) emitting the cyan component (62) during a photopic period, with a Melanopic D65 Efficiency Factor (MDEF) above 1.25 for light sources that emit white light with a CCT between 6500K and 20000K or non-white colored light and above 5.43 - (9.31 *v’) for light sources that emit white light with a CCT between 2000K and 6500K or non-white colored light, where v’ is the corresponding chromaticity coordinate in the CIE 1976 chromaticity diagram (CIELUV color space), wherein: wherein SPD(λ) is the spectral power distribution of the light emitted by the light source, m(λ) is the melanopic sensitivity function, and V(λ) is the photopic sensitivity function.

Said at least one processor may be configured to control, via said at least one control interface, said one or more light sources to render further light with said cyan component and without said UV component before said light with said UV component and said cyan component is rendered. By rendering the cyan component even before the UV component is rendered (but during the photopic period), the circadian rhythm may be made stronger before the UV component is rendered.

Said at least one processor may be configured to control said one or more light sources to render light with said UV component only when controlling said one or more light sources to render light with said UV component and said cyan component. This is beneficial, because rendering light with a UV component but without a cyan component has a larger risk of harming a person’s health.

Said at least one processor may be configured to control said one or more light sources to render said cyan component in a pulsating manner while said UV component is being rendered. Alternatively, said at least one processor may be configured to control said one or more light sources to render said cyan component continuously while said UV component is being rendered.

Said at least one processor may be configured to determine said current time of day, determine said period of the day, and determine whether said current time of day falls in said period of the day by comparing said current time of day with said period of the day. Said at least one processor may be configured to determine said period of the day based on an identifier of a current geographical location, for example. This makes it possible to determine whether said current time of day falls in said period of the day without a light sensor and allows a personal circadian period to be used.

Said at least one processor may be configured to determine an identifier of a person and determine said period of the day by determining which period of the day is associated with said identifier of said person. This personal circadian period is beneficial when a user’s internal rhythm is different from the geolocational rhythm, e.g. when a user is travelling across time zones. In this case, the person’s circadian rhythm has not adapted to the local daylight period yet and there is a risk of the UV light harming the person’s health during part of the local daylight period.

This personal circadian period is also beneficial for persons that have nightshifts. In the event that a person needs to be awake during the night and asleep during the day, it is beneficial to reverse the biorhythm of the person, i.e. prepare the body for daytime activities like muscle strength, metabolism and cognition during the night, by rendering cyan-enhanced bright light at least for a few hours at the start of the night activity and by providing darkness during the day, when the body needs to restore. Simultaneously, at the moment the biorhythm is in sync with the required activity -rest pattern, UV light can be added to also enhance the bodily processes regulated by UV light.

For those travelling across time zones, the out-of-sync period is of a shorter duration. A cyan enhanced bright light boost in early morning when travelling to the east or a bright light boost in the evening when travelling to the west for a few days prior to travelling will help the body have an activity-rest pattern that is more in sync with the new daytime and as such promotes the beneficial effects of UV light.

Said at least one processor may be configured to a determine an adjusted period of the day based on said period of the day and an identifier of a current geographical location and associate said adjusted period of the day with said identifier of said person. For example, the first day of travelling, the personal circadian period will be more similar to the daylight period at the user’s original location than to the daylight period at the user’s new location and then, each day the personal circadian period will become more similar to the daylight period at the user’s new location until they are the same.

Said at least one processor may be configured to determine whether said current time of day falls in said period of the day by using a light sensor. This makes it possible to determine whether said current time of day falls in said period of the day without determining a geographical location and without access to a database of sunrise and sunset times per geographical location. However, this requires a light sensor at a suitable location.

Said at least one processor may be configured to render said UV light component with a daily average standard erythemal dose of 0.01 to 10. A daily average standard erythemal dose (SED) may be limited to 10 to ensure that the UV radiation does not have (significant) adverse effects, although a dose lower than 10 SED is preferable.

To reduce the risk of sunburn, it is important that a person is only exposed to UV-B light with an erythemal dose per day that is significantly below the sunburn threshold values. These values are different for the different (Fitzpatrick) skin types, the palest white skin tones being the most sensitive to sunburn. For example, the sunburn threshold value for the most sensitive skin type, skin type I, is 2.5 SED. As long as the daily UV exposure is significantly below 2.5 SED (threshold value for skin type I), there is very little risk of UV skin damage, while cutaneous Vitamin D3 can be produced in the skin.

Said light may comprise further components which make said light look white. This allows the benefits of UV irradiation to be provided by a general illuminating device.

In a second aspect of the invention, a method of controlling one or more light sources to render UV light comprises determining whether a current time of day falls in a period of the day which is associated with daylight and controlling said one or more light sources to render light simultaneously comprising a UV component and a cyan component in dependence on said current time of day falling in said period of the day. Said method may be performed by software running on a programmable device. This software may be provided as a computer program product.

Moreover, a computer program for carrying out the methods described herein, as well as a non-transitory computer readable storage-medium storing the computer program are provided. A computer program may, for example, be downloaded by or uploaded to an existing device or be stored upon manufacturing of these systems.

A non-transitory computer-readable storage medium stores at least one software code portion, the software code portion, when executed or processed by a computer, being configured to perform executable operations for controlling one or more light sources to render UV light.

The executable operations comprise determining whether a current time of day falls in a period of the day which is associated with daylight and controlling said one or more light sources to render light simultaneously comprising a UV component and a cyan component in dependence on said current time of day falling in said period of the day.

As will be appreciated by one skilled in the art, aspects of the present invention may be embodied as a device, a method or a computer program product. Accordingly, aspects of the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro- code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a "circuit", "module" or "system." Functions described in this disclosure may be implemented as an algorithm executed by a processor/microprocessor of a computer. Furthermore, aspects of the present invention may take the form of a computer program product embodied in one or more computer readable medium(s) having computer readable program code embodied, e.g., stored, thereon.

Any combination of one or more computer readable medium(s) may be utilized. The computer readable medium may be a computer readable signal medium or a computer readable storage medium. A computer readable storage medium may be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples of a computer readable storage medium may include, but are not limited to, the following: an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. In the context of the present invention, a computer readable storage medium may be any tangible medium that can contain, or store, a program for use by or in connection with an instruction execution system, apparatus, or device.

A computer readable signal medium may include a propagated data signal with computer readable program code embodied therein, for example, in baseband or as part of a carrier wave. Such a propagated signal may take any of a variety of forms, including, but not limited to, electro-magnetic, optical, or any suitable combination thereof. A computer readable signal medium may be any computer readable medium that is not a computer readable storage medium and that can communicate, propagate, or transport a program for use by or in connection with an instruction execution system, apparatus, or device.

Program code embodied on a computer readable medium may be transmitted using any appropriate medium, including but not limited to wireless, wireline, optical fiber, cable, RF, etc., or any suitable combination of the foregoing. Computer program code for carrying out operations for aspects of the present invention may be written in any combination of one or more programming languages, including an object oriented programming language such as Java(TM), Smalltalk, C++ or the like and conventional procedural programming languages, such as the "C" programming language or similar programming languages. The program code may execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer, or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider).

Aspects of the present invention are described below with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the present invention. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor, in particular a microprocessor or a central processing unit (CPU), of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer, other programmable data processing apparatus, or other devices create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in a computer readable medium that can direct a computer, other programmable data processing apparatus, or other devices to function in a particular manner, such that the instructions stored in the computer readable medium produce an article of manufacture including instructions which implement the function/act specified in the flowchart and/or block diagram block or blocks.

The computer program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other devices to cause a series of operational steps to be performed on the computer, other programmable apparatus or other devices to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide processes for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks.

The flowchart and block diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of devices, methods and computer program products according to various embodiments of the present invention. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the blocks may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustrations, and combinations of blocks in the block diagrams and/or flowchart illustrations, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and computer instructions.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention are apparent from and will be further elucidated, by way of example, with reference to the drawings, in which:

Fig. 1 is a block diagram of a first embodiment of the system;

Fig. 2 shows a first example of UV and cyan light components being rendered over time;

Fig. 3 shows a second example of UV and cyan light components being rendered over time;

Fig. 4 is a block diagram of a second embodiment of the system;

Fig. 5 is a flow diagram of a first embodiment of the method;

Fig. 6 is a flow diagram of a second embodiment of the method;

Fig. 7 is a flow diagram of a third embodiment of the method;

Fig. 8 illustrates a daylight period associated with a person being adjusted when the person is travelling; and

Fig. 9 is a block diagram of an exemplary data processing system for performing the method of the invention.

Corresponding elements in the drawings are denoted by the same reference numeral.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Fig. 1 shows a first embodiment of the system for controlling one or more light sources to render UV light: a mobile device 1. A lighting device 23 is capable of rendering UV light and a lighting device 24 is capable of rendering cyan light, i.e. light comprising wavelengths in the range 470-520 nm. The lighting devices 23 and 24 are co- located. The mobile device I is able to control the lighting devices 23-24 via a wireless LAN access point 17 and a bridge 21, e.g. with the help of a light control app running on the mobile device 1. The wireless LAN access point 17 is connected to the Internet 15. An Internet server 13 is also connected to the Internet 15. In the embodiment of Fig. 1, the mobile device 1 and the lighting devices 23-24 communicate via the bridge 23. In an alternative embodiment, the mobile device 1 and one or more of the lighting devices 23-24 can communicate directly. The Internet server 13 may store a database of sunrise and sunset times per geographical location and/or information on personal circadian periods, for example.

The mobile device 1 comprises a receiver 3, a transmitter 4, a processor 5, memory 7, a GPS receiver 8 and a display 9. The processor 5 is configured to determine whether a current time of day falls in a period of the day which is associated with daylight and control, via the transmitter, the lighting devices 23-24 to render light simultaneously comprising a UV component and a cyan component in dependence on the current time of day falling in the period of the day.

In the embodiment of Fig. 1, the processor 5 is configured to determine the current time of day, determine the period of the day based on an identifier of a current geographical location determined with GPS receiver 8, and determine whether the current time of day falls in the period of the day by comparing the current time of day with the period of the day. For example, the processor 5 may be configured to transmit, via transmitter 4, the identifier of the current geographical location to the Internet server 13 and receive, via the receiver 3, the associated period of the day in return.

The UV component may comprise an UV-B component, for example. The cyan component comprises wavelengths in the range 470-520 nm. The processor 5 is further configured to render the UV light component with a daily average standard erythemal dose of 0.01 to 10. In the embodiment of Fig. 1, the lighting device 24 is further capable of rendering further components which make the light rendered by the lighting devices 23-24 look white. The term white light relates to light having a correlated color temperature (CCT) between about 2000 K and 20000 K and within about 10 to 15 SDCM (standard deviation of color matching) from the BBL (black body locus).

In the embodiment of the mobile device 1 shown in Fig. 1, the mobile device 1 comprises one processor 5. In an alternative embodiment, the mobile device 1 comprises multiple processors. The processor 5 of the mobile device 1 may be a general-purpose processor, e.g. from ARM or Qualcomm or an application-specific processor. The processor 5 of the mobile device 1 may run an Android or iOS operating system for example. The display 9 may comprise an LCD or OLED display panel, for example. The display 9 may be a touch screen display, for example. The memory 7 may comprise one or more memory units. The memory 7 may comprise solid state memory, for example.

The receiver 3 and the transmitter 4 may use one or more wireless communication technologies, e.g. Wi-Fi (IEEE 802.11) for communicating with the wireless LAN access point 17, for example. In an alternative embodiment, multiple receivers and/or multiple transmitters are used instead of a single receiver and a single transmitter. In the embodiment shown in Fig. 1, a separate receiver and a separate transmitter are used. In an alternative embodiment, the receiver 3 and the transmitter 4 are combined into a transceiver. The mobile device 1 may comprise other components typical for a mobile device such as a battery and a power connector. The invention may be implemented using a computer program running on one or more processors.

In the embodiment of Fig. 1, the system of the invention is a mobile device. In an alternative embodiment, the system of the invention is a different device, e.g. a lighting device. In the embodiments of Fig. 1, the system of the invention comprises a single device. In an alternative embodiment, the system of the invention comprises a plurality of devices.

Figs. 2 and 3 shows examples example of UV and cyan light components being rendered over time. In both examples, the UV component 61 is only rendered when the cyan component 62 is also rendered. In other words, when the UV component 61 is rendered, the cyan component 62 is also rendered. The UV component 61 is only rendered during the daylight period 66, which starts at time 64 and ends at time 65.

In the example of Fig. 2, light simultaneously comprising the UV and cyan components 61 and 62 is rendered during an interval 67. Further light with the cyan component 62 and without the UV component 61 is rendered before this light is rendered.

The cyan component 62 is rendered during interval 68, which starts before interval 67. When the current time becomes time 69, the rendering of the UV component 61 starts.

In the example of Fig. 2, the cyan component 62 is rendered continuously during interval 68. In the example of Fig. 3, the cyan component 78 is rendered in a pulsating manner while the UV component 61 is being rendered. The cyan component 78 may be rendered every minute, for example. The UV component 61 is rendered during interval 77 and the cyan component 62 is rendered during interval 78. In the example of Fig. 3, the cyan component 62 is not rendered before the UV component 61 is rendered.

The intensity of the UV component 61 may stay the same during the interval 77 or may depend on the current time of day, i.e. following natural light, or on the current stage of the personal circadian period. For example, the intensity of the (artificial) UV component 61 may depend on the intensity of the UV light received from the sun at the new user location or the old user location. For instance, the artificial UV light may only be rendered when the measured lux is larger than 500. The intensity of the cyan component 62 may stay the same during the interval 78 or may depend on the current time of day.

The intensity of the UV component 61 and/or duration of interval 77 may depend on the amount of UV irradiation to which the user has already been exposed, e.g. as measured by a personal light sensor, and/or on personal characteristics like sleep hours and work hours. The intensity of the cyan component 62 and/or duration of interval 78 may depend on the amount of cyan light to which the user has already been exposed, e.g. as measured by a personal light sensor, and/or on personal characteristics like sleep hours and work hours. The intensity of the UV component 61 and/or duration of interval 77 and the intensity of the cyan component 62 and/or duration of interval 78 may be set independently.

The light source emitting the UV component 61 may be a white emitting light source having UV with a daily average dose of 0.01 SED (standard erythemal dose) to 10 SED, but it may also be a non-white light source fulfilling the UV dose requirements. The light source emitting the cyan component 62 may also be a white emitting light source or a non-white emitting light source. A single light source may emit light comprising both the UV component and the cyan component. This light source may comprise, for example, UV LEDs and white LEDs or cyan (blue-green) LEDs or a combination of those, giving high melanopic activation during most of the photopic period when the UV LEDs are on.

Preferably, the light source emitting the cyan component 62 has been designed and/or is controlled in such a way that during the photopic period, the Melanopic D65 Efficiency Factor (MDEF; also known as Melanopic Efficacy Ratio or MDER) is above 1.25 for light sources that emit white light with a CCT between 6500K and 20000K or non-white colored light and above 5.43 - (9.31 *v’) for light sources that emit white light with a CCT between 2000K and 6500K or non-white colored light, where v’ is the corresponding chromaticity coordinate in the CIE 1976 chromaticity diagram (CIELUV color space).

MDEF is a value without units. Preferably, during the scotopic period, the MDEF is below 0.2 for light sources that emit non-white colored light and below 5.43 - (9.31 *v’) for light sources that emit white light with a CCT between 2000K and 6500K. MDEF can be determined with the following equation: wherein SPD(λ) is the spectral power distribution of the light emitted by the light source (typically expressed as Watt per wavelength), m(λ) is the melanopic sensitivity function, and the V(λ) is the photopic sensitivity function.

As described above, the term white light relates to light having a correlated color temperature (CCT) between about 2000 K and 20000 K and within about 10 to 15 SDCM (standard deviation of color matching) from the BBL (black body locus). The melanopic sensitivities and photopic sensitivities for wavelengths in the range 380 to 780 nm are listed in Table 1.

Table 1

Fig. 4 shows a second embodiment of the system for controlling one or more light sources to render UV light: a lighting device 31. The lighting device 31 is capable of rendering UV light and cyan light. A mobile device 41 is able to control the lighting device 31 via a wireless LAN access point 17 a bridge 21, e.g. with the help of a light control app running on the mobile device 41. In the embodiment of Fig. 1, the mobile device 41 and the lighting device 31 communicate via the bridge 21. In an alternative embodiment, the mobile device 41 and the lighting device can communicate directly, e.g. using Bluetooth technology.

The lighting device 31 comprises a receiver 33, a transmitter 34, a processor 35, a LED module 39 and a control interface 36 between the processor 35 and the LED module 39. The LED module 39 comprises a plurality of LEDs, e.g. a UV LED, a blue LED and a green LED.

The processor 35 is configured to determine whether a current time of day falls in a period of the day which is associated with daylight and control, via the control interface 36, the LED module 39 to render light simultaneously comprising a UV component and a cyan component in dependence on the current time of day falling in the period of the day.

In the embodiment of Fig. 4, the lighting device 31 is not capable of rendering further components which make the light rendered by the lighting device 31 look white. In an alternative embodiment, the lighting device 31 is capable of rendering such further components, e.g. the LED module 39 may comprise a white LED and/or red, green and blue LEDs.

In the embodiment of Fig. 4, the processor 35 is configured to determine whether the current time of day falls in the period of the day by using a light sensor 43. In the embodiment of Fig. 4, the light sensor 43 transmits data to the lighting device 31 via the bridge 21. In an alternative embodiment, the light sensor 43 transmits data to the lighting device 31 directly.

In the embodiment of the lighting device 31 shown in Fig. 4, the lighting device 31 comprises one processor 35. In an alternative embodiment, the lighting device 31 comprises multiple processors. The processor 35 of the lighting device 31 may be a general- purpose processor or an application-specific processor. The receiver 33 and the transmitter 34 may use one or more wireless communication technologies e.g. Zigbee, for communicating with the bridge 21. In an alternative embodiment, multiple receivers and/or multiple transmitters are used instead of a single receiver and a single transmitter.

In the embodiment shown in Fig. 4, a separate receiver and a separate transmitter are used. In an alternative embodiment, the receiver 33 and the transmitter 34 are combined into a transceiver. The lighting device 31 may comprise other components typical for a connected lighting device such as a power connector and a memory. The invention may be implemented using a computer program running on one or more processors. A first embodiment of the method of controlling one or more light sources to render UV light is shown in Fig. 5. A step 101 comprises determining whether a current time of day falls in a period of the day which is associated with daylight. In the embodiment of Fig. 5, steps 111 and 113 implement step 101. Step 111 comprising receiving light measurement data from a light sensor. Step 113 comprises determining whether the current time of day falls in a period of the day which is associated with daylight based on the light measurement data received in step 111. If the measured light intensity Li equals or exceeds a threshold T, step 103 is performed next. If not, then step 111 is repeated.

Step 103 comprises controlling the one or more light sources to render light simultaneously comprising a UV component and a cyan component. Step 111 is repeated after step 103, after which the method proceeds as shown in Fig. 5. The method of Fig. 5 may be performed by the lighting device of Fig. 4, for example.

A second embodiment of the method of controlling one or more light sources to render UV light is shown in Fig. 6. Step 101 comprises determining whether a current time of day falls in a period of the day which is associated with daylight. In the embodiment of Fig. 6, steps 131-137 implement step 101.

Step 131 comprises determining the current time of day t _cur Step 133 comprises determining an identifier of a current geographical location. Step 135 comprises determining the period of the day P based on the identifier of the current geographical location determined in step 133. Period of the day P may be period 66 of Fig. 2, for example. Step 137 comprises comparing the current time of day t _cur determined in step 131 with the period of the day P determined in step 135. If the current time of day t _cur falls in the period of the day P, step 103 is performed next. If not, steps 131 and/or 133 are performed next, after which the method proceeds as shown in Fig. 6.

Step 103 comprises controlling the one or more light sources to render light simultaneously comprising a UV component and a cyan component. Step 101 is repeated after step 103, after which the method proceeds as shown in Fig. 6. In the embodiment of Fig.

6, step 131 is performed at least partly in parallel with steps 133 and 135. In an alternative embodiment, step 131 is performed before step 133 or after step 135.

A third embodiment of the method of controlling one or more light sources to render UV light is shown in Fig. 7. Step 101 comprises determining whether a current time of day falls in a period of the day which is associated with daylight. In the embodiment of Fig.

7, steps 131, 137, 151 and 153 implement step 101. Step 131 comprises determining the current time of day t _cur Step 151 comprises determine an identifier of a person. Step 153 comprises determine the period of the day P by determining which period of the day is associated with the identifier of the person determined in step 151. Period of the day P may be period 66 of Fig. 2, for example. Step 137 comprises comparing the current time of day t _cur determined in step 131 with the period of the day P determined in step 153. If the current time of day t _cur falls in the period of the day P, steps 103 and 133 are performed next. If not, steps 131 and/or 151 are performed next, after which the method proceeds as shown in Fig. 7.

Step 103 comprises controlling the one or more light sources to render light simultaneously comprising a UV component and a cyan component. Step 133 comprises determining an identifier of a current geographical location. Step 135 comprises determining a further period of the day based on the identifier of the current geographical location determined in step 133. A step 157 is performed after step 135.

Step 157 comprises determining an adjusted period of the day based on the period of the day determined in step 153 and the further period of the day determined in step 135. Next, a step 159 comprises associating the adjusted period of the day with the identifier of the person. The adjusted period may be different from the period of the day determined in step 153 as a result of the user travelling or as a result of the daylight period (sunrise time and/or sunset time) changing throughout the year, which happens in many geographical locations. Step 101 is repeated after one or both of steps 103 and 159 have been performed, after which the method proceeds as shown in Fig. 7.

In the embodiment of Fig. 7, step 131 is performed at least partly in parallel with steps 151 and 153. In an alternative embodiment, step 131 is performed before step 151 or after step 153. In the embodiment of Fig. 7, steps 133-135 and 157-159 are only performed if it is determined in step 137 that the current time of day t _cur falls in the period of the day P. In an alternative embodiment, steps 133-135 and 157-159 are performed independent of the outcome of step 137.

Fig. 8 shows examples of the (daylight) period determined in step 153 and the adjusted (daylight) periods determined in step 157 of Fig. 7 when a user is travelling. The daylight period associated with the user starts at time 64 and ends at time 65. The daylight period at the current geographical location starts at time 84 and ends at time 85. Timelines 81-83 represent these two daylight periods at consecutive days.

On the first day, represented by timeline 81, the user is at home or near his home and has not travelled recently. As a result, the daylight period associated with the user (starting at time 64 and ending at time 65) matches the daylight period at his home (starting at time 84 and ending at time 85)

On the second day, represented by timeline 82, the user is travelling and arrives at a different geographical location where the sun rises a few hours earlier and sets a few hours earlier. In the example of Fig. 8, the day is shorter at the new geographical location. In the timeline 82, the daylight period associated with the user (starting at time 64 and ending at time 65) has not been adjusted yet based on the daylight period associated with the different geographical location (starting at time 84 and ending at time 85) and is therefore the same as in timeline 81. An adjusted daylight period is determined and associated with the user on the second day, but it is not used yet.

On the third day, represented by timeline 83, the user is still at the different geographical location and this day, the adjusted time period, which was determined the previous day, is used. The daylight period associated with the user has been adjusted such that its start time and end time are closer to the start time and end time of the daylight period at the user’s current geographical location, i.e. the different geographical location. The start time and the end time of the daylight period associated with the user may be shifted by maximum one hour, for example. By limiting the adjustment to this personal daylight period (also referred to as personal circadian period), the adjustment in the user’s circadian rhythm is reflected in this personal daylight period.

In the example of Fig. 8, an adjusted daylight period is determined on the second day, but not used until the third day. Alternatively, the adjusted daylight period determined on the second day is already used on the second day.

Fig. 9 depicts a block diagram illustrating an exemplary data processing system that may perform the method as described with reference to Figs. 5-7.

As shown in Fig. 9, the data processing system 300 may include at least one processor 302 coupled to memory elements 304 through a system bus 306. As such, the data processing system may store program code within memory elements 304. Further, the processor 302 may execute the program code accessed from the memory elements 304 via a system bus 306. In one aspect, the data processing system may be implemented as a computer that is suitable for storing and/or executing program code. It should be appreciated, however, that the data processing system 300 may be implemented in the form of any system including a processor and a memory that is capable of performing the functions described within this specification. The memory elements 304 may include one or more physical memory devices such as, for example, local memory 308 and one or more bulk storage devices 310. The local memory may refer to random access memory or other non-persistent memory device(s) generally used during actual execution of the program code. A bulk storage device may be implemented as a hard drive or other persistent data storage device. The processing system 300 may also include one or more cache memories (not shown) that provide temporary storage of at least some program code in order to reduce the quantity of times program code must be retrieved from the bulk storage device 310 during execution. The processing system 300 may also be able to use memory elements of another processing system, e.g. if the processing system 300 is part of a cloud-computing platform.

Input/output (I/O) devices depicted as an input device 312 and an output device 314 optionally can be coupled to the data processing system. Examples of input devices may include, but are not limited to, a keyboard, a pointing device such as a mouse, a microphone (e.g. for voice and/or speech recognition), or the like. Examples of output devices may include, but are not limited to, a monitor or a display, speakers, or the like. Input and/or output devices may be coupled to the data processing system either directly or through intervening I/O controllers.

In an embodiment, the input and the output devices may be implemented as a combined input/output device (illustrated in Fig. 9 with a dashed line surrounding the input device 312 and the output device 314). An example of such a combined device is a touch sensitive display, also sometimes referred to as a “touch screen display” or simply “touch screen”. In such an embodiment, input to the device may be provided by a movement of a physical object, such as e.g. a stylus or a finger of a user, on or near the touch screen display.

A network adapter 316 may also be coupled to the data processing system to enable it to become coupled to other systems, computer systems, remote network devices, and/or remote storage devices through intervening private or public networks. The network adapter may comprise a data receiver for receiving data that is transmitted by said systems, devices and/or networks to the data processing system 300, and a data transmitter for transmitting data from the data processing system 300 to said systems, devices and/or networks. Modems, cable modems, and Ethernet cards are examples of different types of network adapter that may be used with the data processing system 300.

As pictured in Fig. 9, the memory elements 304 may store an application 318. In various embodiments, the application 318 may be stored in the local memory 308, the one or more bulk storage devices 310, or separate from the local memory and the bulk storage devices. It should be appreciated that the data processing system 300 may further execute an operating system (not shown in Fig. 9) that can facilitate execution of the application 318.

The application 318, being implemented in the form of executable program code, can be executed by the data processing system 300, e.g., by the processor 302. Responsive to executing the application, the data processing system 300 may be configured to perform one or more operations or method steps described herein.

Fig. 9 shows the input device 312 and the output device 314 as being separate from the network adapter 316. However, additionally or alternatively, input may be received via the network adapter 316 and output be transmitted via the network adapter 316. For example, the data processing system 300 may be a cloud server. In this case, the input may be received from and the output may be transmitted to a user device that acts as a terminal.

Various embodiments of the invention may be implemented as a program product for use with a computer system, where the program(s) of the program product define functions of the embodiments (including the methods described herein). In one embodiment, the program(s) can be contained on a variety of non-transitory computer-readable storage media, where, as used herein, the expression “non-transitory computer readable storage media” comprises all computer-readable media, with the sole exception being a transitory, propagating signal. In another embodiment, the program(s) can be contained on a variety of transitory computer-readable storage media. Illustrative computer-readable storage media include, but are not limited to: (i) non-writable storage media (e.g., read-only memory devices within a computer such as CD-ROM disks readable by a CD-ROM drive, ROM chips or any type of solid-state non-volatile semiconductor memory) on which information is permanently stored; and (ii) writable storage media (e.g., flash memory, floppy disks within a diskette drive or hard-disk drive or any type of solid-state random-access semiconductor memory) on which alterable information is stored. The computer program may be run on the processor 302 described herein.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of embodiments of the present invention has been presented for purposes of illustration, but is not intended to be exhaustive or limited to the implementations in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the present invention. The embodiments were chosen and described in order to best explain the principles and some practical applications of the present invention, and to enable others of ordinary skill in the art to understand the present invention for various embodiments with various modifications as are suited to the particular use contemplated.