This invention relates to a light monitoring system according to the preamble of the first claim.

The present invention also relates to a light monitoring system network and a method for operating the light monitoring system or the light 5 monitoring system network.

WO2011135524, for example, describes a skylight for spreading daylight in a building as described in the preamble of the first claim. The skylight described by WO2011135524 comprises a daylight spreading device, to be mounted in a roof opening of the building, and a mirror device. The mirror0 device is rotatably mounted above the daylight spreading device and provided for reflecting light to the daylight spreading device. The mirror device further comprises a mirror, a motor for rotating the mirror device and a controller for controlling the motor. The controller is arranged so that the mirror device is brought to an optimal position in which as much light as possible is reflected5 towards the daylight spreading device. The controller comprises a measuring device, provided for measuring the intensity of the incident light on the mirror. The measuring device is provided with a first and a second light sensor and a shade element, arranged to create a shadow on the first or second light sensor, and a processing unit for processing the intensity measured by the light0 sensors. The controller is provided for determining an adjusted optimal position based on the luminous intensity measured by the first and second light sensor.

Although such a skylight allows light to be spread more optimally in the building, it was found that in some circumstances insufficient light is available in the building at certain locations, for example because insufficient5 light is available to be reflected by the mirror device towards the daylight spreading device, for example because the sun is partly occluded by clouds and/or has already partly or completely disappeared below the horizon, for example at night.

In such conditions it was necessary to employ an artificial light source or sources, present beforehand or not, to obtain sufficient light at the locations. However, such controlling of one or more artificial light sources requires a manual intervention involving someone switching on the artificial light source, which costs time and is often imprecise so that the light source is often switched on too soon or switched off too late, or the switching off of the light source is even forgotten. In this, energy, often electricity, is unnecessarily spent in powering the artificial light source.

Therefore an aim of the present invention is to provide a light monitoring system according to the preamble of the first claim whereby an improved control of the artificial light source is achieved.

This aim is achieved according to the invention using a light monitoring system exhibiting air the characteristics of the first claim.

To that end, the processing unit is provided to convert the luminous intensity measured by the light sensors to an expected illuminance at a predetermined location inside the building, and to control the artificial light source(s) correspondingly, so as to achieve a predefined minimum illuminance or even a predefined illuminance at the predetermined location.

It was found that such control of the artificial light source allows achieving a predefined minimum illuminance or even a predefined illuminance at the predetermined location in the building without requiring manual intervention, so that a more precise switching on and off of the artificial light source is achieved.

Although light monitoring systems are already known wherein artificial light sources are controlled in accordance with a measured luminous intensity of light, such light monitoring systems always require additional light sensors to be provided. For example, US 6,340,864 B1 describes a light monitoring system wherein a light sensor is provided at a location for controlling an artificial light source in accordance with measured light at the location. Such a system, however, always requires an additional light sensor to be installed, which is often undesirable as such a light sensor takes up space, can be inadvertently covered by objects and/or persons, often requires powering, etc.

It was found that with the present invention, on the one hand, the first and the second light sensor allow the mirror device to be controlled in such a way that a more optimal position of the mirror device is obtained and thus more light is reflected towards the daylight spreading device, and on the other hand, the luminous intensity measured by the first and the second light sensor can be used to determine the expected illuminance at a predetermined location without requiring additional light sensors to be installed. That way, an improved lighting can be achieved at the predetermined location without recourse to additional light sensors, as a predefined illuminance is always achieved without unnecessary use of the artificial light source and with maximal use of the naturally available light outside the building. In addition, it was found that by controlling the artificial light source in such a way, the control of the artificial light source is less dependent on specific conditions in the building, such as for example placement, color, dimensions, etc. of furniture, floors, walls, etc.

Although WO0032015 already describes using a light sensor inside a skylight to control an artificial light source in accordance with light measured by the sensor, this publication only teaches to replace, if possible, the light transmitted by the artificial light sources by light from the skylight. WO0032015 does not take into account the nature of the incident light in the skylight, nor the illuminance expected by the people at a certain location to be able, for example, to do their jobs. For example, no distinction is made between a homogeneously lit sky and a sky with a distinct light source, for example a sky with a sun not occluded by clouds, for example a clear sky. Such different conditions, however, exert a significant influence on the illuminance at the predetermined location, particularly when, as in the present invention, a mirror device is provided. Moreover, the configuration described in WO0032015 does not allow taking into account all artificial light sources. For example, artificial light sources not mounted within range of the daylight spread by the skylight cannot be taken into account. Moreover, the configuration described by WO0032015 seems geared mainly toward use in a domestic dwelling, and less or not at all towards use in other locations such as for example professional working spaces such as for example a factory hall, which are generally much more spacious and/or much higher, use other types of lighting and optionally even require different illuminances.

However, since the processing unit according to the present invention is provided to convert the luminous intensity measured by the light sensors to an expected illuminance at a predetermined location inside the building, for example a location where work will actually be done, for example at a location which is closer to the floor than to the ceiling, for example a location at eye height of an average person, for example when standing or sitting, for example a location at working height of a person, for example at the height of an average desktop, etc., and to control the artificial light source correspondingly so as to achieve a predefined illuminance at the predetermined location, the illuminance expected by the people to be able, for example, to do their jobs without, for example, excessively switching on the available light sources, is taken into account. Moreover, environmental factors such as for example color/nature of the walls, etc., are taken into account, as is the configuration of all artificial light sources. Because of this, if was found that, for example, the present invention is also suited for applications outside the domestic dwelling, such as for example professional working spaces such as, for example, factory halls.

According to preferred embodiments of the present invention, the processing unit is provided to determine an illuminance on the light sensors based on the luminous intensity measured by the light sensors, and to determine the expected illuminance at the predetermined location in the building based on the determined illuminance on the light sensors. Such a configuration allows the expected illuminance to be determined with sufficient accuracy at the predetermined location in the building.

According to preferred embodiments of the present invention, the processing unit is provided to take into account the height at which the mirror device is mounted above the predetermined location in determining the expected illuminance. Consequently, in such a configuration, the position of the predetermined location in relation to the mirror device is taken into account as well, so that the illuminance at the actual location, for example the location where people actually come, for example a working space such as an office, workshop, etc., can be taken into account.

According to further preferred embodiments of the present invention, the processing unit is provided to determine the expected illuminance at the predetermined location based on a quotient, wherein the processing unit is provided to determine the quotient by dividing a reference luminous flux at a reference location by the squared height between the reference location and the predetermined location. It was found that, surprisingly, such a simple calculation nevertheless yields reliable results.

According to further preferred embodiments of the present invention, the processing unit is provided to determine the reference luminous flux based on the luminous intensity measured by the light sensors. For example, the reference location is approximately 1 meter below the bottom part of the skylight, for example the ceiling of the building.

According to further preferred embodiments of the present invention, the processing unit is provided to calculate a product, wherein the product is obtained by multiplying the quotient with a predetermined correlation factor, wherein the expected illuminance is the product. It was found that this correlation factor allows the inclusion of a plurality of environmental factors, such as for example the nature/color of the walls, position of the predetermined location in relation to the mirror device, etc.

According to preferred embodiments of the present invention, the correlation factor is determined by dividing an illuminance previously measured at the predetermined location by the quotient determined at that moment. It was found that such a simple determination of the correlation factor still allows calculation of a reliable predefined illuminance- According to preferred embodiments of the present invention, the artificial light source is outside the range of the daylight spread by the skylight.

The adjusted optimal position is determined from a difference between the luminous intensity measured by the first sensor and that measured by the second sensor. This difference in luminous intensity is caused by the shade from the shade element, which falls on the first/second sensor when the position of the mirror device is not optimal.

Also achieved by the measuring device and the controller according to the invention is the finding and storing of the optimal position, based on actual measurements of the intensity of the incident light on both sensors, which is a measure for the intensity of the incident light on the mirror. This way, an incorrect position of the mirror device, which in the art can arise through an error in the time and/or the position on the earth's surface, can be prevented according to the invention, while control remains simple. Furthermore, an optimal orientation of the mirror device can this way be achieved during the day, taking into account local obstacles or elements producing shadow, such as for example an antenna cabinet next to the skylight, high-rise building in the vicinity, a difference in pitch on one and the same roof, etc.

According to preferred embodiments of the present invention, the light sensors are located above the ceiling of the predetermined location. Such a configuration offers the advantage that the sensors remain easily accessible via the daylight spreading device, preferably via the roof of the building. In addition, the need for cables in the building is avoided and the sensors are less dependent on the specific situation in the building, for example furniture placement, wall colors, etc. Moreover, sensors mounted this way are less visible, which is considered more aesthetic by viewers. In addition, the sensors remain out of reach of persons in the building, thus reducing the risk of damage, accidental or intentional covering, etc.

According to preferred embodiments of the present invention, the light monitoring system comprises at least two skylights, and the processing unit comprises a central processing unit and a respective local processing unit for each of the skylights, wherein the local processing units are connected to the central processing unit and the central processing unit is connected to the artificial light source, wherein the respective local processing units are arranged for processing of the luminous intensities measured by the respective light sensors in the respective skylights, and the central processing unit is arranged for controlling the artificial light source based on the respective luminous intensities processed by the local processing units and transmitted to the central processing unit. Such a configuration allows the local processing units to be arranged to provide control of an adjusted optimal position of the mirror device, and the central processing unit to be arranged to control the artificial light source so as to provide a more optimal lighting of the predetermined location. Although the connection between the central processing unit and the local processing unit can occur for example by an electric signal through an electrically conductive wire, with the connection for that purpose comprising a physical communication network, for example a physical computer network, the connection can also be implemented by means of a wireless communication network, with the connection for that purpose comprising a wireless communication network. A wireless communication network offers the advantage that no physical network needs to be provided and that remote skylights can also be included in the light monitoring system.

According to preferred embodiments of the present invention, the light monitoring system comprises at least two artificial light sources. In such a configuration, control of the artificial light sources is significantly simplified compared to the previous manual control of the artificial light sources, as control of the artificial light sources becomes more complicated, especially with a plurality of artificial light sources, thus increasing the risk of unnecessary energy consumption for powering the artificial light sources.

According to preferred embodiments of the present invention, the artificial light source is a lamp such as for example a tubular lamp, an incandescent lamp, etc.

According to preferred embodiments of the present invention, the artificial light source is an electrically powered artificial light source such as for example a tubular lamp, an incandescent lamp, etc.

According to preferred embodiments of the present invention, the processing unit is arranged to determine, based on the luminous intensity measured by the first and the second sensor and the time during which the artificial light source is powered, the amount of saved energy compared to continuous powering of the artificial light source. Using the determined amount of energy saved in comparison with continuous powering of the artificial light source, the performance of the light monitoring system can be determined and/or tracked. Moreover, it becomes possible to charge a user of the light monitoring system a fee based on the determined energy saved, allowing for example an installer of the light monitoring system to charge a user of the light monitoring system a fee for the use of the light monitoring system based on the energy saved by the user, which would normally have been consumed by the artificial light source or sources.

According to preferred embodiments of the present invention, the light monitoring system comprises an interface where a user of the light monitoring system can consult one or more of the following: the amount of energy saved in comparison with continuously powering the artificial light source, the powering of the artificial light source, the luminous intensity measured by the first and/or second sensor, the illuminance determined by the processing unit, for example the central processing unit and/or local processing units, the illuminance determined at the predetermined location, the measured yield of the daylight spreading device, the position of the mirror device, the voltage on the battery, etc. Optionally, such an interface can also allow entry of certain parameters of the light monitoring system such as for example one or more of the following parameters: the predefined illuminance, the height at which the mirror device is mounted above the floor of the predetermined location, the number of windows around the predetermined location, etc.

According to preferred, embodiments of the present invention, the controller is provided with means for determining a zero position, for example an electronic compass or reed switch(es) for determining a zero position, preferably oriented substantially eastward, such that the position of the mirror position is already substantially optimal at sunrise.

According to preferred embodiments of the present invention, the controller is arranged for finding an initial optimal position during a full rotation of the mirror device. The initial optimal position can be found by executing a full rotation of the mirror device and determining at which orientation the measured luminous intensity is highest. This execution can serve as an alternative to the means for determining a zero position, for example the electronic compass or reed switch(es), or as a complement to it. According to preferred embodiments of the present invention, the controller is arranged for determining the adjusted optimal position when a difference value, calculated using the luminous intensities measured by the first and second light sensor respectively, exceeds a predetermined threshold, and for periodically determining the difference value. Such a controller allows determining when it is necessary to find a more optimal position, using the existing light sensors.

According to further preferred embodiments of the present invention, the difference value equals the absolute value of a value based on a difference (d) between luminous intensities measured by the first and second light sensor respectively, divided by a value based on a sum (s) of the luminous intensities measured by the first and second light sensor respectively, for example \dls\. Such an absolute value proves to be a good criterion for determining when a more optimal position needs to be found. It was found that the predetermined threshold is preferably 0,01 and that the adjusted optimal position is preferably only determined if the difference value is greater than 0,01 , i.e., for example, \d/s\ > 0,01 , as a good positioning can be achieved at such a value while avoiding excessive repositioning and its resultant energy consumption.

According to preferred embodiments of the present invention, the controller is arranged to determine the adjusted optimal position by rotating the mirror device, based on a reference value calculated using the luminous intensities measured by the first and second light sensor respectively. Such a reference value allows determination of the adjusted optimal position by using the values from the light sensors themselves.

The reference value further preferably equals a quotient of a value based on a difference of luminous intensities measured by the first and second sensor respectively, and a value based on a sum of luminous intensities measured by the first and second sensor respectively. It was found that a good adjusted optimal position can be obtained based on such a reference value. Preferably, based on the reference value, the mirror device is rotated clockwise if the reference value is greater than 0, and rotated anticlockwise if the reference value is smaller than 0.

The controller is further preferably arranged to control the motor, as long as the difference value exceeds the predetermined threshold, in such a way that the mirror device rotates in accordance with the reference value, until the difference value no longer exceeds the predetermined threshold. For example, a cycle is run by the controller as long as the difference value exceeds the predetermined threshold, preferably 0,01. During every step of the cycle, the mirror device is rotated in accordance with the reference value by the motor controlled by the controller, preferably for a predetermined time or for a predetermined angle. If, after such a rotation of the mirror device, the reference value for example falls below the predetermined threshold, the cycle stops.

The values based on a difference of luminous intensities measured by the first and second light sensor respectively, are preferably determined by averaging at least two differences of at least two pairs of luminous intensities measured by the first and second light sensor respectively at different times. The values based on a sum of luminous intensities measured by the first and second light sensor respectively are preferably determined by averaging at least two sums of at least two pairs of luminous intensities measured by the first and second light sensor respectively at different times. The same corresponding measured luminous intensities are used for both the sum and the difference.

For example, some luminous intensities measured substantially simultaneously by the first and second light sensor respectively are stored in order to calculate these average values. Preferably at least 2, but more preferably 5 values of the first and second light sensor respectively are measured at same moments and stored, to calculate a corresponding number of times, i.e. preferably 5 times, a sum and a difference, wherein the difference is in each case the luminous intensity measured by the first light sensor minus the luminous intensity measured by the second light sensor, after which the average is taken of respectively the sums and the differences so that an average of the sums, preferably 5, and an average of the differences, preferably 5, is obtained. Based on these, the reference value and the difference value are then determined, wherein the difference value is the absolute value of the reference value.

In embodiments of the present invention, the controller is arranged to replace, as long as the difference value exceeds the predetermined threshold, at least one of the at least two pairs of values measured by the first and second light sensor with a pair of values measured by the first and second light sensor after or during the rotation of the mirror device. The controller is preferably arranged to replace, while running the cycle, the at least one, preferably periodically, stored values measured by the first and second light sensor with values measured by the first and second light sensor after or during the rotation of the mirror device, in order to adjust the difference value to the adjusted position of the mirror device so that can be determined if the mirror device should keep turning to assume an optimal position. Further preferably, for this purpose, the oldest of the stored values are replaced by the values measured last. For example, at the end of each cycle new values are measured and stored, replacing the current oldest stored values.

According to preferred embodiments of the present invention, the controller is arranged for periodically looking for the adjusted optimal position. Further preferably, the period for looking for the adjusted optimal position is shorter than 10 minutes, such as for example 5 minutes. This allows energy to be saved, as an adjusted position is not continuously looked for.

Further preferably, the controller is arranged to look for the adjusted optimal position after a prolonged period if the measured luminous intensities differ insufficiently from each other over time. It was found that in such case mirror device is for example prevented from following the reflection of a cloud, where for example more light can be captured in a different position. By waiting a longer period, it was found that, for example, the cloud moves away and a significantly new position needs to be found that is possibly better.

The controller is preferably arranged for measuring, before, preferably immediately before each, preferably periodical search for the adjusted optimal position, the at least 2, preferably 5, pairs of substantially simultaneously measured values of luminous intensities using the first and second light sensor. This is preferably done by measuring the luminous intensities shortly before looking for the optimal position, for example 30 seconds before determining the optimal position. Further preferably, this is done for example 5 times, with 5 to 6 seconds between each measurement, during the 30 seconds before looking for the optimal position. In preferred embodiments the controller is arranged, when the first and second light sensor are saturated by the radiation of the sun when by rotating the mirror device the difference value no longer exceeds the predetermined threshold, for controlling the motor in such a way that it causes the mirror device to rotate on again, preferably for a predetermined time and/or angle. Such a controller also allows solving an incorrect position caused by the saturation of the light sensors.

The invention also relates to a light monitoring system network of several light monitoring systems according to the present invention, wherein the respective central processing units of the respective light monitoring systems are interconnected. Such a system allows the different light monitoring systems to be controlled and/or tracked centrally, for example through an interface. Preferably, a separate central processing unit is provided for every building. The different central processing units are for example connected via a computer network, for example the internet. The light monitoring system network preferably also comprises a central computer server to which the different central processing units are connected. The connection to the central computer server can for example comprise a wireless connection such as for example a 2G/3G, WiFi, etc. connection, but can also be connected by means of a physical connection.

The invention also relates to a method for operating the light monitoring system according to the present invention, wherein the processing unit converts the luminous intensity measured by the light sensors to an expected illuminance at a predetermined location inside the building, and controls the artificial light source correspondingly, so as to achieve a predefined illuminance at the predetermined location. According to preferred embodiments of the present invention, the processing unit determines an expected illuminance at the predetermined location in the building, based on the luminous intensity measured by the light sensors. Such a configuration allows the expected illuminance to be determined with sufficient accuracy at the predetermined location in the building.

According to preferred embodiments of the present invention, the processing unit is arranged to take into account one or more of the following factors when determining the expected illuminance: the height at which the mirror device is mounted above the predetermined location, for example the floor, the number of windows around the location, etc.

According to preferred embodiments of the present invention, the processing unit takes into account the height at which the mirror device is mounted above the predetermined location when determining the expected illuminance.

More specifically, the processing unit preferably determines the expected illuminance at the predetermined location based on a quotient, wherein the processing unit determines the quotient by dividing , a reference luminous flux at a reference location, for example approximately 1 meter below the bottom part of the skylight, for example the ceiling of the building, by the squared height between the reference location and the predetermined location. Further preferably, the processing unit determines the reference luminous flux using the luminous intensity measured by the light sensors.

According to preferred embodiments of the present invention, the processing unit calculates a product, wherein the product is obtained by multiplying the quotient with a predetermined correlation factor, wherein the expected illuminance is the product.

According to preferred embodiments of the present invention, the correlation factor is determined by dividing a illuminance previously measured at the predetermined location by the quotient determined at that moment.

For example, based on previous measurements for the specific light sensors that are used and the specific skylight that is used, it is determined how a measured luminous intensity on the sensor relates to a determined reference luminous flux at 1 meter below, for example, the bottom part of the skylight, for example the ceiling of the building. By dividing this reference luminous flux by the squared height to the predetermined location from the place for which the reference illuminance was determined, the illuminance can be determined at the predetermined location. When the illuminance is then actually measured at the predetermined location, the measured illuminance can be correlated with the illuminance determined using the measured luminous intensity, by a correlation factor. It was found that, by then further multiplying the illuminance determined using the measured luminous intensity with the correlation factor, a good approximation can be obtained of the true illuminance at the predetermined location, based on the illuminance determined using the measured luminous intensity at the light sensors of the skylight.

According to preferred embodiments of the present invention, the light monitoring system comprises at least two skylights and the processing unit comprises a central processing unit and a respective local processing unit for each of the skylights, wherein the local processing units are connected to the central processing unit and the central processing unit is connected to the artificial light source, wherein the respective local processing units process the luminous intensities measured by the respective light sensors in the respective skylights, and the central processing unit controls the artificial light source based on the respective luminous intensities processed by the local processing units and transmitted to the central processing unit. Such a configuration allows the local processing units to be arranged to provide control of an adjusted optimal position of the mirror device, and the central processing unit to be arranged to control the artificial light source so as to provide a more optimal lighting of the predetermined location. Although the connection between the central processing unit and the local processing unit can occur for example by an electric signal through an electrically conductive wire, with the connection for that purpose comprising a physical communication network, for example a physical computer network, the connection can also be implemented by means of a wireless communication network, with the connection for that purpose comprising a wireless communication network. A wireless communication network offers the advantage that no physical network needs to be provided and that remote skylights can also be included in the light monitoring system.

According to preferred embodiments of the present invention, the light monitoring system comprises at least two artificial light sources. In such a configuration, control of the artificial light sources is significantly simplified compared to the previous manual control of the artificial light sources, as control of the artificial light sources becomes more complicated, especially with a plurality of artificial light sources, thus increasing the risk of unnecessary energy consumption for powering the artificial light sources.

According to preferred embodiments of the present invention, the processing unit determines, based on the luminous intensity measured by the first and the second sensor and the time during which the artificial light source is powered, the amount of saved energy compared to continuous powering of the artificial light source. Using the determined amount of energy saved in comparison with continuous powering of the artificial light source, the performance of the light monitoring system can be determined and/or tracked. Moreover, it becomes possible to charge a user of the light monitoring system a fee based on the determined energy saved, allowing for example an installer of the light monitoring system to charge a user of the light monitoring system a fee for the use of the light monitoring system based on the energy saved by the user, which would normally have been consumed by the artificial light source or sources. It also becomes possible to track the operation of the system by the same route, and thus to track and optionally improve the long-term performance, or to perform repairs by the same route without being physically present (for example uploading new software, resetting a local or central processing unit, re-initialising motor, and mirror, etc.).

The invention will be further elucidated through the following description and the appended figures.

Figure 1 shows a longitudinal section of a preferred embodiment of a skylight of a light monitoring system according to the invention. Figure 2 shows a cross section of a preferred embodiment of a skylight of a light monitoring system according to the invention.

Figure 3 shows a perspective view of a preferred embodiment of a skylight of a light monitoring system according the invention.

Figure 4 shows a perspective view of a transfer of a preferred embodiment of a skylight of a light monitoring system according the invention.

Figure 5 shows schematically a printed circuit board with an operating system for a preferred embodiment of a skylight of a light monitoring system according to the invention.

Figure 6 shows an overview of a light monitoring system according to the invention.

The skylight shown in Figure 1-3 comprises a prismatic lens 10 above the roof opening, a light shaft 11 with reflective walls through the roof opening and a pyramidal lens or second prismatic lens 12 below the roof opening, which together form a daylight spreading device for spreading incident daylight/sunlight falling on top the roof opening in the building. Above the prismatic lens is a rotatably mounted mirror device 1 , to reflect the incident daylight and/or sunlight through the light shaft 1 under a transparent dome 13.

The transparent dome 13 is for example made from high quality transparent polycarbonate (with double UV coating), or any other transparent material known in the art. The base of the dome 13 is square, but may optionally also be circular or any other shape considered suitable by the person skilled in the art. The dome preferably forms an airtight seal at the top of the whole and serves as a weatherproof shield for the mirror device. The dome is preferably attached by a combination of glue and screws as prevention against burglary.

The light shaft 11 for example has side panels made from SPO material or sheet material which receives a highly reflective white coating (based on zirconium as an environmentally friendly alternative to reflective mirror foil) and the top and bottom of the light shaft are closed by specially tailored optical elements. The top element is the prismatic lens 10, a flat lens made of polycarbonate with a pattern for optimum reception and transmission of light. The bottom element is the, for example prismatic, pyramid lens 12, a polycarbonate lens in a pyramid shape, preferably with a prismatic pattern, for optimum light distribution within the building. Other embodiments are also possible, such as for example a second flat prismatic lens. Besides collecting, enhancing, reflecting and spreading the incoming light, the two lenses 10, 12 also create a stationary layer of air in the shaft 11 , causing the system to be thermally insulating. The daylight spreading device 10-12 can also be formed by any other combination of optical elements known to the skilled person.

Preferably a moisture absorbent element is also included in order to combat condensation.

The mirror device 1 comprises a first arm 2 which supports a mirror 3 at an angle of preferably about 65° with respect to the surface of the earth, and a second arm 4 on which a printed circuit board 5 with a measuring device and a processing unit is mounted. The PCB 5 is mounted substantially near the top of the mirror 3 and preferably oriented in a direction substantially perpendicular to the surface of the earth, or alternatively in a 45° angle to the surface. It can be seen that the PCS 5, having light sensors 6, 7 thereon, is located above the ceiling of the predetermined location.

The mirror 3 is preferably a flat mirror, but can also be a mirror with two folded corners of which one is positive and one is negative. The mirror is preferably placed at a fixed angle of 50 to 80°, more preferably 60 to 70°, most preferably about 65° with respect to the surface of the earth, although other angles are also possible if circumstances require so. In alternative embodiments, the mirror device generally comprises one or more flat or curved mirrors, mounted under the same or at different angles relative to the surface of the earth. In an alternative embodiment, the mirror 3 may also be tiltably mounted on the mirror device 1 , with a tilting mechanism which may also be controlled on the basis of a measurement of the luminous intensity, such as two sensors with a partition as described herein but with the sensors superimposed instead of parallel.

The printed circuit board (PCB) 5, schematically shown in Figure

5, comprises an operating system with a measuring device 6-9 for measuring the luminous intensity incident on the mirror 3 and a processing unit 14 for processing the measured intensity. The measuring device is formed by a first light sensor 6 and a second light sensor 7 next to each other with a partition 8 in the middle between them. This partition 8 constitutes a shade element for creating a shadow on the first or second light sensor, if the position of the mirror device 1 differs from the currently optimal position. In the optimal position the light sensors 6 and 7 measure almost the same intensity. On the PCB 5 a protective wall 9 is also arranged above the first and second sensor 6, 7 for shielding the incident light on that side, which benefits the accuracy of the measurement. The processing unit 14 compares the luminous intensity measured by the sensors 6 and 7, and concludes from a difference whether the mirror device is to be rotated to the left or to the right, depending on where the measured luminous intensity is highest. When adapting, the mirror device 1 is rotated until the intensity measured by the sensors 6, 7 is substantially equal again.

In alternative embodiments, a combination of multiple light sensors may be provided, such as, next to the first and second sensor, also a third sensor to accurately distinguish day from night. According to the invention there are at least two sensors, but more than two is also possible.

In the embodiment shown in the figures, the measuring device 6-9 and the processing unit are provided on the same circuit board 5. This is not essential for the invention and may also be done differently.

The partition 8 and the shielding wall 9 are preferably also made of PCB material with a black masking layer, or another essentially non- reflective material known to the skilled person, to counter the reflection of the light.

Specifically, the two light , sensors 6 and 7 are light-sensitive sensors which produce a voltage proportional to the incident light. These are for example PV cells which can deliver a certain power at incident light, over a resistor of 1Mohm, leading to a voltage of about 3V at 30Klux. An amplifier may be placed in buffer mode after the sensor to buffer the voltage and absorb a power surge. If the sensors 6 and 7 are optimally directed to the sun or another optimal light spot, both sensors receive substantially the same light and produce an equal voltage. Otherwise - if the position differs from the optimum - one of the sensors will receive more light than the other sensor and both sensors will produce a different voltage. This voltage is used by the processing unit to determine the optimal position.

The processing unit runs an algorithm which is preferably constructed in such a way that, once a certain minimum (e.g. 300lux or OOOlux) incident light is measured, a light measurement is carried out periodically (e.g. every minute or every five minutes) seeking the optimal point of light. Then the motor is controlled to focus the mirror thereto. At dusk, when the minimum incident light is no longer met, the system is set in readiness for the start of the next cycle. Preferably, an electronic compass is thereto integrated on the printed circuit board 5, or for example one, but preferably more such as for example two reed switches are connected to the printed circuit board. Herewith, a zero position can be created in the east, to which the mirror device can return every 24h and begin a new cycle from this position. Thus each cycle begins in the vicinity of the expected optimal position and the mirror device can quickly be brought to the optimal position.

The motor 15, which drives the rotation of the mirror driving device 1 , is preferably but not necessarily an electric stepper motor that can rotate in both directions (e.g., speed 0.2 rpm). The motor is for example a DC motor with a control consisting of two half-bridges to control in both directions. The electrical power for the installation is provided by the combination of a solar panel 16 with a rechargeable battery with an autonomy of 3 weeks for example. This way no mains power supply needs to be provided. Obviously, the electric power may also be provided in other ways known in the art, such as for example a mains power supply.

The dome preferably is provided with an anti-fogging agent, such as for example silica gel or a box of active clay, to absorb potential condensation and controlling humidity in the dome.

The control unit on the printed circuit board 5 is preferably provided with a temperature sensor measuring the ambient temperature inside the dome. The components used are of the industrial class, which means that the allowable temperature range is -20°C to +85°C. If the temperature inside the dome would rise above 85°C, the operation would be shut down for safety reasons. In the case of several skylights being provided on the building in close proximity to each other, each dome preferably has its own individual operating system so that they operate independently with regards to orientation of the mirror device. In this way, it is not necessary to create a link between different domes on the same roof for orienting the mirror device. There are no settings (location coordinates or other) to be entered during installation on the roof. Once the power supply (solar panel and battery) is connected, each skylight operates autonomously and immediately for orienting the mirror device.

Figure 6 shows an overview of a preferred embodiment of a light monitoring system according to the invention.

The processing unit 14 is provided to convert the luminous intensity measured by the light sensors 6, 7 to an expected illuminance at a predetermined location inside th building, and to control the artificial light source 17 correspondingly, so as to achieve a predefined illuminance at the predetermined location. The predefined illuminance is for example a minimal illuminance or even a specific predefined value for the illuminance.

According to an embodiment, the artificial light source or sources may for example be switched on as soon as the expected illuminance is lower than the predefined illuminance. According to further embodiments, the switching on of the artificial lighting occurs gradually, for example using a dimmer switch, in proportion to the difference between the expected illuminance and the predefined illuminance

The light monitoring system show preferably but not necessarily comprises at least to skylights 18, 19, and the processing unit 14 preferably but not necessarily comprises a central processing unit 20 and a respective local processing unit 21 , 22 for each of the skylights 18, 19. The local processing units 21 , 22 are connected to the central processing unit 20 and the central processing unit 20 is connected to the artificial light source 17. The respective local processing units 21 , 22 are arranged for processing of the luminous intensities measured by the respective light sensors in the respective skylights 18, 19, and the central processing unit 20 is arranged for controlling the artificial light source 17 based on the respective luminous intensities processed by the local processing units 21 , 22 and transmitted to the central processing unit 20.

The connection between the local processing units 21 , 22 and the central processing unit 20 as shown in Figure 6 preferably comprises a wireless communication network 23. However, other connections are also possible, such as for example a physical network by means of for example cables.

As shown in Figure 6, the processing unit 14 preferably controls a plurality of artificial light sources 17.

Figure 6 also shows a central processing location 24 where information from the central processing unit 20 for example arrives, for example for storing information to enable charging a user of the light monitoring system for the use of the light monitoring system based on the energy saved by using the light monitoring system according to the present invention.

Moreover, using the previously described light monitoring system network of several light monitoring systems according to the present invention, wherein the respective central processing units 20 of the respective light monitoring systems are interconnected, for example through a network 25, more specifically a physical or wireless network, and in this location a central collection location may be provided to, for example, collect and store the data of the different light monitoring systems, and/or to host the interface. This can for example be done by means of a computer server. Such a computer server obviously does not need to be housed at a central location but can also be housed in various locations, according to the preference of the server manager.

Although the present invention was described by means of one specific embodiment, it is clear that various changes can be applied without exceeding the protection scope of the conclusions. In this sense, the description and figures should be seen as examples, and should not be construed in a strict sense.