WO2008135942A1

WO2008135942A1 - Lighting device and control method

Info

Publication number: WO2008135942A1
Application number: PCT/IB2008/051727
Authority: WO
Inventors: Rabin Bhattacharya; Chantal Sweegers; Leendert Van Der Tempel; Jacob Klerk
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2007-05-07
Filing date: 2008-05-05
Publication date: 2008-11-13
Also published as: TW200913781A

Abstract

The present invention relates to a lighting device (10), comprising: at least one light source (12); a detector (16) for detecting the distance (d) to an object; and a control unit (14) adapted to turn on the light source(s) upon detection of the distance if the at least one light source is off, and to adjust the brightness of the light source(s) in relation to the detected distance. The present invention also relates to a method for controlling a lighting device.

Description

Lighting device and control method

FIELD OF THE INVENTION

The present invention relates to a lighting device and a method for controlling a lighting device.

BACKGROUND OF THE INVENTION

An example of a lighting device, in particular an automatic lighting device, is disclosed in the document "New research in the light and health field is expanding the possibilities for LED lighting in healthcare environments" by Mariana G. Figueiro and Mark S. Rea, CIE Midterm Meeting Conference Proceedings, Leon, Spain, 2005. Specifically, the cited document discloses a light emitting diode (LED) based lighting device comprising an array of amber LEDs whereto a passive infrared (PIR) motion sensor is connected. Upon detection of motion, for instance the appearance of a person in the room in which the LED array is installed, the LEDs are ramped up to full on. The LEDs are then turned off after three minutes if no motion is detected. Such a solution permits the LEDs to be in the on state only when necessitated by a nearby moving person, allowing power saving, etc.

SUMMARY OF THE INVENTION

In view of the above prior art, it is an object of the present invention to provide an improved lighting device, which in particular is more versatile and allows more power saving.

These and other objects that will be apparent from the following description are achieved by means of a lighting device, and a method for controlling a lighting device, according to the appended claims.

According to one aspect of the invention, there is provided a lighting device comprising: at least one light source; a detector for detecting the distance to an object; and a control unit adapted to turn on the light source(s) upon detection of the distance if the at least one light source is off, and to adjust the brightness of the light source(s) in relation to the detected distance. Thus, when any distance within the range of the detector is detected (i.e. the presence of an object), it is ensured that the light source is on, and the brightness or intensity of light emitted by the light source when it is turned on is determined by the specific distance detected by the detector. Further, as the detected distance changes, so does the brightness of the light source. This should be compared to the above mentioned prior art solution where the light source is always full on irrespective of the distance to the object. When no further distance is detected, the light source may be kept on at the set brightness level for a predetermined period of time and may then be turned off. An illumination area or direction of the at least one light source may at least partly coincide with that of the detector, whereby the illumination of an object or its immediate surroundings changes as it moves closer to or away from the lighting device.

The present lighting device thus provides for automatic control and adjustment of the brightness level (gradually between off and full on), with optimal illumination, power saving, versatility, etc. as a result, as will be explained further below. In one embodiment, the control unit may set a higher intensity of the emitted light when a closer distance is detected, and set a lower intensity when a farther distance is detected. This could advantageously be used in a store where a display area, for instance a shelf with products, is lit up more and more as a customer (object) approaches it to make it appear more evident. Contrary, a lower intensity may be set for a shorter detected distance, and a higher intensity for a longer distance. Such a setup may be advantageous in the case where the object itself is lit by the light source: a farther object may need higher intensity to become illuminated to a desired degree, while for a closer object a lower intensity is enough. This avoids glare and/or over exposure and promotes power saving (no brighter light than necessary is used).

An exemplary detector of the present lighting device is adapted to transmit a longer range signal and a shorter range signal; and receive any reflection(s) of the transmitted signals off the object, whereby reception of the reflection of the longer range signal indicates a longer distance and reception of the reflection of the shorter range signal indicates a closer distance. Hereto, the resolution of the distance detector can be increased by transmitting additional signals of different, intermediate ranges. Further, in the lighting device, a specific intensity of the light source is preferably associated with a specific transmitted signal for effortless operation. Assume for instance that three signals having different ranges are transmitted. When for instance the light source is initially off, and if no reflected signal is detected, the light source remains off. If reflection of the longest range signal then is detected (but not that of any shorter range), the light source goes from being completely off to the dimmest level. Further, if reflection of the intermediate range signal after that is detected (and also that of the longer range, but not that of the shortest range), the light source's intensity is increased one step. Finally, if reflection of the shortest range signal is detected, the light source is turned to its brightest level. The above detector may for instance be an infrared based detector transmitting IR signals by means of an IR light emitting diode (LED) and receiving reflections by means of an IR sensor.

Instead of the exemplary detector, other proximity sensors known per se could be used, for instance an electric field or an ultrasonic proximity sensor.

The present lighting device is preferably of a type where light is introduced in a light guide, preferably a thin light guide plate, by means of the at least one light source. In the light guide, the light may be mixed before it is extracted by means of a plurality of out- coupling structures. Hereto, the at least one light source may be a plurality of LEDs, in particular side emitting LEDs arranged in the light guide, and the out-coupling structures may be tilted reflectors for extracting light perpendicularly to the plane of the light guide plate. LEDs offer several advantages over traditional light sources, such as long lifetime, low operating voltage, etc. Further, mixing light from multiple LEDs in the light guide and the out-couple is beneficial when the light of a single LED is not sufficient and light of multiple LEDs needs to be combined to form a luminous source. Instead of LEDs, other appropriate light sources could be used, such as other semiconductor light sources (e.g. laser diodes).

In a further embodiment, the lighting device moreover comprises at least one additional light source adapted to emit light; a second detector for detecting the distance to an object; and a second control unit adapted to turn on the at least one additional light source upon detection of the distance by the detector if the at least one additional light source is off, and to adjust the brightness of the additional light source(s) in relation to the distance detected by the second detector. This embodiment allows the light sources of the lighting device to follow the movement of an object, such as a person. As the object passes by, the illumination is automatically adjusted accordingly, providing optimal illumination and power saving. For instance, when an object such as a person first situated in an area serviced by the firstly mentioned detector and light source(s) moves to an adjacent, partly overlapping area serviced by the secondly mentioned detector and light source(s), the light gradually shifts from the first to the second light source(s). The at least one additional light source and the second detector may be of the same types as the firstly mentioned light source and detector described above. Further, the second control unit may be a separate control unit, or its functions could be incorporated in the above firstly mentioned control unit. According to another aspect of the invention, there is provided a method for controlling a lighting device comprising at least one light source, the method comprising: detecting the distance to an object; turning on the light source(s) upon detection of the distance, if the at least one light source is off; and adjusting the intensity of the light emitted by the at least one light source in relation to the detected distance. This aspect exhibits similar advantages as the previously discussed aspect of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing currently preferred embodiments of the invention.

Fig. 1 is a block diagram of a lighting device according to an embodiment of the present invention.

Fig. 2 is a flow diagram describing a method for controlling the lighting device of fig. 1. Figs. 3a-3d schematically show an exemplary operation of an exemplary detector which can be used in the lighting device of fig. 1.

Fig. 4 is a schematic view of lighting device according to another embodiment of the present invention.

DETAILED DESCRIPTION

Fig. 1 is a block diagram of a lighting device 10 according to an embodiment of the present invention. The lighting device 10 is preferably an illumination device adapted to illuminate one or more objects.

The lighting device 10 comprises at least one light source 12. The light source 12 may for instance be one or more light emitting diodes (LEDs). The light source 12 is connected to a control unit 14 generally adapted to govern the output of the light source(s) 12 by supplying appropriate commands or currents or voltages.

The control unit 14 is further connected to a detector 16. The detector 16 is adapted to detect the distance d (from the detector 16) to an object 18. The range of the detector 16 and the direction of the detector 16 help determining an area 20 where the object 18 may be detected and the distance d may be determined. In some applications, the detector area 20 may at least partly coincide with an illumination area 22 of the light source 12, but in some applications the detector area 20 may be separate from the illumination area 22 (as in fig. 1).

The control unit 14 is further adapted to turn on the light source 12, if the light source 12 is not already on, upon detection of any distance d by the detector 16, and to adjust the brightness or intensity of the light source 12 in relation to the particular distance d to the object 18 as detected by the detector 16. If the light source 12 is initially on, it remains on when the distance is detected, but the brightness is adjusted in accordance with the detected distance.

Hereto, in an exemplary operation of the lighting device 10, the light source 12 is initially on or off. The on state could be either a dimmed level or full on, depending on the application. If no distance d is detected by the detector 16 at this stage, the control unit 14 will not change the state of the light source 12, hence it remains on or off. However, if an object 18 appears at the perimeter of the detector area, a distance d to the object is detected by the detector 16, and the control unit 14 consequently turns the light source 12 on if it was not already on. The brightness of the light source 12 when in the on state, i.e. the intensity of the light emitted by the light source 12 when on, depends on the distance to the object as detected by the detector. As the perimeter of the detector area 20 generally represents the farthest distance detectable, it may correspond to an extreme value of the light source brightness. Depending on the application, the extreme value could mean that the light source 12 here is set to full on or to the dimmest level. If the object then gets closed, i.e. a shorter distance d is detected by the detector 16, the control unit 14 automatically adjusts the brightness or output of the light source accordingly. That is, from full on the brightness is decreased, while from the dimmest level the brightness is increased. If the distance then again increases, the brightness is increased or decreased accordingly. At the closest detectable distance d, the light source 12 may be set at the lowest brightness level (or completely turned off), or at the highest brightness level, again depending on the application. When no distance is detected indicating no object 18 in the detection area 20, the light source 12 may remain on at the set level for a predetermined period of time starting from the moment of the last detection, and is then turned off or it goes back to a predetermined level, if no more distance is detected. Thus, the light source 12 may remain on even if the object temporarily exits the detection area. The method of operation or control of the lighting device 10 comprising steps Sl -S3 is summarized in fig. 2.

It should be noted that the presence of the object may be indicated as an addition to a distance measurement only. If no distance is detected (e.g. there is no object or the object is out of range), there is consequently no presence. On the other hand, if a distance is detected, then consequently there is also a presence. Similar, motion may be detected: if the detected distance changes there is motion, and if the detected distance is constant there is no motion. Motion detection capability according to known techniques (e.g. PIR) may also be added to the detector 14 to enhance the presence/motion detection. A specific distance detector 16' adapted for use in the above lighting device will now be described with reference to figs. 3a-3d. The distance detector 16' comprises an IR transmitter 24 (e.g. and IR LED) and an IR receiver 26. The IR transmitter is adapted to transmit IR signals of various ranges. Here, three different signals each having a specific range rX may be transmitted, but the number of ranges can be changed depending on the desired resolution. The signals having the different ranges may be achieved by pulsing the IR LED 24 with different current levels, where the highest current level corresponds to the signal having longest range and the lowest current level corresponds to the signal having the shortest range.

The transmitted signals may then be reflected by the object, and depending on which reflected signals that are received by the IR receiver 26, the distance to the object is determined. Advantageously, a certain brightness or dimming level of the light source 12 to be set is associated with each different signal.

Assume for instance three different signals ranges rl-r3 as discussed above, rl is the shortest range, r2 is an intermediate range, and r3 is the longest range. Assume also that the light source is initially off. If no reflected signal is detected (i.e. the object 18 is outside the longest range r3), the light source will then remain off (fig. 3a). If reflection r'3 of the longest range signal r3 then is detected (but not that of any shorter range), the light source goes from being completely off to the dimmest level ("light source low", fig. 3b). Further, if reflection r'2 of the intermediate range signal r2 then is detected (and also that of the longer range r3, but not that of the shortest range rl), the light source's intensity is increased one step ("light source medium", fig. 3c). Finally, if reflection r' l of the shortest range signal rl is detected, the light source is turned to its brightest level ("light source high", fig. 3d). It should be noted that the relationship between the signals and brightness levels could be reversed. Also, the initial state of the light source could be different. A lighting device 10' according to another embodiment of the present invention will now be described in relation to fig. 4. The lighting device 10' is based on the lighting device of fig. 1, but comprises additionally at least one second light source 12b and a second detector 16b connected to the control unit 14. The second light source(s) 12b and detector 16b, here arranged at the side of the light source(s) 12 and detector 16, operate similar to the light source(s) 12 and detector 16 described above, but with a different illumination area 20b and detector area 22b. The illumination areas 20, 20b may coincide with the corresponding detector areas 22, 22b, respectively, while there is a slight overlap between the detector area 22 and detector area 22b as well as a slight overlap between the illumination areas 20 and 20b.

During operation, an object 18, for instance a person, entering the detector area 22 from for instance the left will be illuminated by the at least one light source 12. When the person 18 moves closer, the brightness of the light source 12 will change, preferably it increases. As the person moves further to the right in fig. 4, the brightness will eventually start decreasing as the distance increases. However, in the overlap between detector areas 22 and 22b, the person 18 will be detected also by the second detector 16b, whereby the second light source 12b is initiated. As the person 18 continues to the right, he or she will leave the first detector area 22, resulting in that the first light source eventually will be turned off (given no other object is detected), and while in the second detector area 22b, the intensity of the light source 10b will be adjusted by the control unit 14 similar as above in relation to the current distance between the second detector 16b and the person 18. Eventually, when the person 18 exits the detector area 22b to the right, also the second light source 12b may be turned off. Thus, in the lighting device 10' the movement of the object is tracked and the output light is adjusted accordingly. It should be noted that further light sources and detectors could be provided for following movements over larger areas.

It should further be noted that the lighting device of fig. 4 may be embodied without the distance dependent brightness adjustment. Instead, the light sources may "digitally" be turned on/off or switched between two levels. Such a lighting device or system may then comprise a first detector adapted to detect the presence of an object in a first area; a second detector adapted to detect the presence of an object in a second area; at least one first light source associated with the first detector; at least one second light source associated with the second detector; and a control unit adapted to actuate the first light source(s) when an object is detected by the first detector and to actuate the second light source(s) when an object is detected by the second detector. Such a device or system may advantageously follow and illuminate a moving object, such as a person. Actuate means here for instance turning the light sources on or changing (preferably increasing) the brightness of the light sources. The present lighting device as discussed above is preferably of a type where light is introduced in a light guide, preferably a thin light guide plate, by means of the at least one light source. In the light guide, the light may be mixed before it is extracted by means of a plurality of out-coupling structures. Hereto, the at least one light source may be a plurality of LEDs, in particular side emitting LEDs arranged in the light guide, and the out-coupling structures may be tilted reflectors for extracting light perpendicularly to the plane of the light guide plate.

Applications of the present lighting device includes various indoor and outdoor illumination systems, in particular systems requiring or benefiting from automatic detection features. The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims.

Claims

CLAIMS:

1. A lighting device (10), comprising: at least one light source (12); a detector (16) for detecting the distance (d) to an object; and a control unit (14) adapted to turn on the light source(s) upon detection of the distance if the at least one light source is off, and to adjust the brightness of the light source(s) in relation to the detected distance.

2. A lighting device according to claim 1, wherein the control unit is adapted to set a higher brightness when a closer distance is detected, and a lower brightness when a farther distance is detected.

3. A lighting device according to claim 1 or 2, wherein the detector is adapted to transmit a longer range signal and a shorter range signal; and receive any reflection of the transmitted signals off the object, whereby reception of the reflection of the longer range signal only indicates a longer distance and reception of the reflection of the shorter range signal indicates a closer distance.

4. A lighting device according to any preceding claim, further comprising: a light guide, wherein the at least one light source is arranged for coupling light into the light guide; and a plurality of out-coupling structures arranged for coupling light out of the light guide.

5. A lighting device according to any preceding claim, wherein the at least one light source comprises at least one light emitting diode.

6. A lighting device according to any preceding claim, further comprising: at least one additional light source; a second detector for detecting the distance to an object; and a second control unit adapted to turn on the additional light source(s) upon detection of the distance by the second detector if the at least one additional light source is off, and to adjust the brightness of the additional light source(s) in relation to the distance detected by the second detector.

7. A method for controlling a lighting device (10) comprising at least one light source (12), the method comprising:

(51) detecting the distance (d) to an object (18);

(52) turning on the light source(s) upon detection of the distance, if the at least one light source is off; and

(53) adjusting the brightness of the light source(s) (12) in relation to the detected distance.