FIELD OF THE INVENTION

The present invention relates to a lighting device having a built in smoke detection function. BACKGROUND OF THE INVENTION

For example in the German utility model publication DE 20219425 it is disclosed that a lamp is equipped with a smoke detector, which can be of any suitable type that is available in the market. The smoke detector is attached at an appropriate part of the lamp, such as at the fastening elements.

It is not convenient to equip just any kind of lighting device with a separate smoke detector, for instance when the lighting device is too small to contain such an apparatus.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a lighting device that alleviates the above-mentioned drawbacks of the prior art.

This object is achieved by a lighting device according to the present invention as defined in claim 1.

The invention is based on an insight that under particular circumstances it is possible to use the light emitted for illuminating purposes by the lighting device itself or a neighboring lighting device to detect smoke in the surrounding air.

Thus, in accordance with an aspect of the invention, there is provided a lighting device comprising a light source, a light coder, a light detector, which is arranged to detect coded light, and an alarm generator. The light coder is connected with the light source for coding the output light of the light source with an individual code. The light detector is located out of direct light impingement from the light source and is arranged to detect the individually coded light after being reflected on smoke particles in the air. The alarm generator is connected with the light detector, wherein the lighting device is arranged to generate an alarm when a smoke detection condition is fulfilled. Within the meaning of the invention a lighting device has as its primary function illuminating spaces, areas, objects, etc.

By using the coded light generated by the lighting device itself or by another lighting device in the vicinity thereof, it is possible to add only a few small parts to the original lighting device without a smoke detector, in order to achieve the smoke detection function. Thereby the lighting device is kept at approximately the same size as without the smoke detector. There is no need for adding a separate complete smoke detector to the lighting device.

In accordance with an embodiment of the lighting device it further comprises a surface reflection blocker, which is arranged to block light reflected by surfaces around the lighting device from reaching the light detector. Thereby the risk of false alarm is minimized.

In accordance with an embodiment of the lighting device, the surface reflection blocker comprises an optical element arranged in front of the detector, wherein the optical element focuses light from a predetermined distance onto the detector. By choosing an appropriate focal length of the optical element only light from a certain (range of) distance(s) is focused on the detector and thereby detectable as a true reflection from particles in the air.

In accordance with an embodiment of the lighting device, the optical element is adjustable. The lighting device comprises an optical scanning controller for scanning the optical element across a scanning area. The adjustability of the optical element is

advantageous in that a larger area can be covered in order to detect smoke.

In accordance with an embodiment of the lighting device, the smoke detection condition is fulfilled when a detection threshold has been exceeded at a predetermined number of scanning positions within the scanning area during a single scanning. This embodiment is even better equipped to avoid false alarms, such as smoke coming from a single candle light that is smoking excessively but harmlessly and happens to be located below the lighting device.

In accordance with an embodiment of the lighting device, the surface reflection blocker comprises a shield, which is arranged in front of and at a distance from the detector such that a portion of the light output from the light source passes through the space between the detector and the shield. This shield provides for a total physical light blocking of reflections from surrounding surfaces, and only particles in the air between the shield and the detector generate an alarm. In accordance with an embodiment of the lighting device, the lighting device is switchable between a high intensity state and low intensity state, where the light source in the low intensity state emits light at an intensity level that is a fraction of the high intensity level but high enough to enable smoke detection. In this way the lighting device can be regarded as turned off but still act as a smoke detector.

In accordance with an embodiment of the lighting device, the light detector is arranged to detect light coded with several different codes. With this embodiment the lighting device is able to detect light reflections of light originating from other lighting devices. Thus, configurations of several lighting devices that co-operate in discovering a fire are

configurable.

In accordance with an embodiment of the lighting device, the individual code is a Code Divisional Multiple Access type code.

In accordance with an embodiment of the lighting device, the lighting device comprises a measuring means arranged to measure the intensity level of the detected light. This measurement is useful for providing more complex decision making than an absolute threshold detection only reacting on a unidirectional passage of the threshold.

In accordance with another aspect of the invention there is provided a lighting system comprising a plurality of lighting devices and a central controller connected to the lighting devices. This lighting system is useful for many purposes of central control of large premises, a building, etc.

In accordance with an embodiment of the lighting system, the central controller is arranged to receive a smoke detection signal from any one of the lighting devices that detects reflected light in excess of a multi detection threshold, which does not fulfill said smoke detection condition, and the central controller is arranged to generate an alarm when receiving smoke detection signals from at least a predetermined percentage of the lighting devices within a predetermined time period. By means of this embodiment it is possible to detect more diffuse smoke clouds, which although not being dens enough to trigger an individual smoke alarm of one of the lighting devices still indicates a serious situation due to their substantial extension.

These and other aspects, features, and advantages of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described in more detail and with reference to the appended drawings in which:

Fig. 1 is a schematic cross-sectional view of an embodiment of a lighting device according to the present invention;

Fig. 2 is a schematic cross-sectional view of another embodiment of a lighting device according to the present invention;

Fig. 3 is a schematic cross-sectional view of an embodiment of a lighting system according to the present invention;

Fig. 4 is a block diagram of the lighting device shown in Fig. 1;

Fig. 5 is a block diagram of another embodiment of the lighting device; and

Fig. 6 is a block diagram of another embodiment of the lighting device and a lighting system.

DESCRIPTION OF PREFERRED EMBODIMENTS

In a first embodiment, as shown in figs. 1 and 4, the lighting device 1 comprises a light source 3, a light coder 5, which is connected to the light source 3, a light detector 7, and an alarm generator 9, which is connected to the light detector 7. Further, the lighting device 1 comprises an optical element 11 , which acts as a surface reflection blocker. Only the parts of the lighting device 1 which are of interest for this description have been shown.

Basically, the lighting device of course has as a main purpose illuminating its surroundings. As a secondary function, it is arranged to generate an alarm when a smoke detection condition is fulfilled.

More particularly, the light coder 5 is arranged to code the output light of the light source 3 with an individual code. For instance, and in this embodiment, the light coder 5 modulates the power that drives the light source. In this embodiment the coding technique is CDMA (Code Division Multiple Access), but many different techniques are usable as understood by a person skilled in the art, e.g. pure frequency modulation. Typically, the light source is a LED (Light Emitting Diode) light source, but other types of codable light sources exist as well, e.g. OLED's, fluorescent lamps, HID lamps, etc.

The light detector 7 is located such that direct light impingement from the light source is prevented. Furthermore, it is arranged to detect the individually coded light after being reflected on smoke particles in the air. The light detector 7 is capable of sorting out the individually coded light and base the output of an alarm triggering signal to the alarm generator 9 on that light only. For carrying out such a function the light detector 7 comprises a detector element 13 and a decoder 15. The detector element 13 detects any light impinging thereon and outputs a corresponding signal to the decoder 15. The decoder 15 is however selective and generates an output signal that is related to correctly decoded light exclusively. Thus, only detected light which is coded with a predetermined individual code renders an output signal from the decoder 15. Furthermore, the decoder 15 is set at a predetermined detection threshold, i.e. the intensity of the detected individually coded light has to exceed the detection threshold before the decoder 15 generates an output signal.

The alarm generator 9 can be any appropriate element, such as a buzzer, a flash light, a combination thereof or some other kind of alarm generator.

The optical element 11 is arranged to block light reflected by surfaces around the lighting device 1 from reaching the light detector. Such reflections could otherwise generate a false alarm. For instance the optical element 11 comprises a lens having an appropriate focal length such that only light coming from a certain distance, or range of distances, will be focused onto the light detector 7. The distance should be chosen to be relatively close to the optical element 11, and, with a typical mounting of the lighting device 1, far from f.i. floor surfaces, table surfaces, and persons passing the lighting device.

In order to further minimize the risk of false alarm, according to a second embodiment, as shown in fig. 5, the optical element 51 is adjustable, and, more particularly, the focal length is variable within a scanning range. The lighting device 50 comprises a local controller 55, which is connected to the optical element 51 for controlling its scanning operation, and to the light detector 53 in order to receive its output signal. By adjusting the optical element 51 the local controller 55 performs a scanning over the scanning range R from one end to the other, and during the scanning the local controller 55 samples the output signal of the light detector 53 at a plurality of positions. Thus, the local controller acts like an optical scanning controller. The light detector only provides a "high" output signal if the received individually coded light exceeds a predetermined detection threshold. If at least a predetermined percentage of the samples indicate a "high" output signal a smoke detection condition is fulfilled, and the local controller 55 feeds an activation output signal to the alarm generator 57.

Further, when having a LED light source the lighting device 1, 50 is typically, although not necessarily, provided with a temperature sensor 17, 58 for monitoring the temperature of the light source 3, 59. The temperature sensor 17, 58 may additionally be used for smoke detection. If the temperature increases beyond a predetermined temperature threshold, and cannot be attributed to the light source 3, 59, then the alarm generator 9, 57 is activated. This predetermined temperature threshold is a temperature that the device does not reach under normal operating conditions. For that matter, in the first embodiment the temperature sensor is connected to the alarm generator 9, and in the second embodiment it is connected to the local controller 55. Furthermore, by providing the local controller with the capability to detect internal erroneous conditions that could cause an excessive temperature, such as f.i. short circuit currents on an internal circuit board, it can rule out an external fire while still raise the alarm because of damage.

In accordance with another embodiment of the lighting device 21, most schematically shown in fig. 2, the surface reflection blocker is embodied by a shield 23, here a plate, which is arranged in front of the light detector 25. The shield is arranged at a small distance from the light detector 25 forming a space between the shield 23 and the light detector 25. The shield 23 is mounted beside the light source 27 in order not to interfere with the main direction and function of the light output, and at a small distance in front of the light source 27 such that still a minor fraction of the light output passes the space.

This embodiment operates as follows. When the air gets filled with smoke some of the smoke enters the space. Then some of the light that previously passed through the space is reflected by the smoke particles in direction towards the light detector 25. When the amount of light reaching the light detector 25 exceeds a detection threshold the light detector 25, or more specifically a decoder circuit thereof, feeds an activation output signal to the alarm generator 29.

Every lighting device embodiment described herein optionally is switchable between an on state, or high intensity state, and a quasi-off state, or low intensity state. In the on state the light source is considered to be lit by a user, i.e. the light source is energized by a full power or possibly a dimmable power but within the on state. In the quasi-off state, the light source is not completely zero powered but energized with a (very) low power, which is just high enough to maintain the smoke detection function of the lighting device. For instance, in case of a LED light source it is energized at a substantially lower duty cycle than in the on state. An appropriate duty cycle in the quasi-off state could be about 0.1% of the on state duty cycle. Thus, the operating costs due to the electricity in the quasi-off state are negligible. It should be noted that the signal quality of the detected light is not dependent of the duty cycle. For instance, the SNR ratio is always the same, whether the lamp is turned quasi-off or on. In accordance with a third embodiment of the lighting device, as shown in fig. 3, it is arranged to operate together with one or more other lighting devices 31 in a lighting system 61. For reasons of simplicity, in fig. 3 merely two lighting devices 31 are shown, however, typically the lighting system comprises many more lighting devices. In this embodiment the lighting device 31 is arranged to be able to decode more than one individual code. Fig. 6 shows a most schematic block diagram with the parts most relevant for this description. Thus, the lighting system 61 comprises a central controller 63 and a plurality of lighting devices 31, connected with the central controller 63 via a data bus 64, such as an Ethernet connection. Each lighting device 31 comprises a local controller 65, a light coder 67, connected to the local controller 65, a light source 69, connected to the light coder 67, a light detector 71 including a detector element 73 and a light decoder 75, connected to the local controller 65, and an alarm generator 77, connected to the local controller 65. In this embodiment the lighting devices do not need to comprise a surface reflection blocker due to a different way of detecting a smoke condition, as will be evident from the description below.

The lighting system 61 operates as follows. At start up, and when a replacement of a lighting device is made, the lighting system 61 is commissioned under the control of the central controller 63. The commissioning includes a learning procedure at start up where each lighting device 31 learns the individual light codes of the other lighting devices 31 , and updates when a lighting device 31 is changed, removed, or added. Further, for each lighting device 31 the intensity level for the light received from each lighting device is measured by means of the detector element 73, and stored at the central controller 63. It should be noted that it is common that for each lighting device 31 the intensity level measured of some of the other lighting devices 31 is zero. Each lighting device monitors the received light intensities. For example, it measures the intensities a number of times per minute. In this lighting system 61 the smoke detection condition is that at least a

predetermined percentage of the received light intensities at a single lighting device 31 should show a significant change from the commissioned value. Assume, as an example, that there are six lighting devices in a room, and that a first one thereof has commissioned levels 0, 0, 0, 1, and 3 from the other lighting devices, and 1 from itself. The highest level can for instance result from a reflection in a shiny metal surface. Assume that a cloud of smoke builds up in the room, and that this causes a change in received intensities to 1, 0, 1, 1, and 2, while the own value changes to 3. That is, due to the smoke the light from most of the lighting devices 31 is more widely spread causing both increased and decreased levels of intensity depending on the original state. Changes in received intensity values are also detected by the other lighting devices 31 to a higher or lower extent. Now assume for instance that the smoke detection condition is that at least 60% of the monitored values should change by at least one unit. The central controller 63 makes a decision based on all values fetched from all lighting devices 31, i.e. 36 values in total. If at least 22 thereof have changed at least one unit the smoke detection condition is fulfilled and a smoke alarm is generated. The alarm can be generated by the central controller 63 activating, via the local controllers 65, the alarm generator 77 one or more of the lighting devices 31.

There are several advantages in having the central controller 63 decide on the smoke detection condition. For example, a smoke alarm can be given with a much higher degree of confidence. The function of having level change as indication instead of the crossing of a predetermined threshold also increases the degree of confidence, and this can be used in the single lighting device applications as well. However, threshold solutions are useful in the lighting system as well.

As an alternative, the evaluation of the smoke detection condition is performed by the local controllers 65, and generates individual alarms.

Lighting devices having a surface reflection blocker of the optical element type are useful in the lighting system as well.

The lighting system with interconnected lighting devices, open up for many different embodiments as regards the smoke detection condition, and depending on the capability of the local controllers different kinds of communication between them and with the central controller are achievable. Furthermore, in this light the central controller may even be omitted if the local controllers are able to communicate and make decisions on a feasible level.

Above, embodiments of the lighting device according to the present invention as defined in the appended claims have been described. These should be seen as merely non- limiting examples. As understood by a skilled person, many modifications and alternative embodiments are possible within the scope of the invention.

Thus, as explained by means of the embodiments above, it is possible to use the light of a lighting device emitting individually coded light to achieve an integrated smoke detection function.

It is to be noted, that for the purposes of this application, and in particular with regard to the appended claims, the word "comprising" does not exclude other elements or steps, that the word "a" or "an", does not exclude a plurality, which per se will be apparent to a person skilled in the art.