FIELD OF THE INVENTION

The present invention relates in general to a lighting device, and in particular to a lighting device arranged to indicate a relation between power and lumen. BACKGROUND OF THE INVENTION

Energy efficiency has become increasingly important. Effective energy- efficient building design can include the use of low cost detectors to switch-off lighting when areas are unoccupied. In addition, light output levels can be monitored using daylight sensors linked to a building's lighting scheme to switch on/off, or dim, the lighting to pre-defined levels to take into account the natural light and thus reduce energy consumption. Despite these potential energy savings and the growing environmental concerns that have existed for years in the world, there still exists a need for improved electric devices and improved lighting devices in general. The advent of digital lighting technologies, i.e., illumination based on semiconductor light sources, such as light-emitting diodes (LEDs), offers a viable alternative to traditional fluorescent, HID, and incandescent lamps. Functional advantages and benefits of LEDs include high energy conversion and optical efficiency, robustness, lower operating costs, and many others. The LEDs' smaller size, long operating life, low energy consumption, and durability make them a great choice in a variety of lighting applications.

According to several different EU Directives (92/75/CEE, 94/2/CE, 95/12/CE,

96/89/CE, 2003/66/CE, et alia) electronic appliances in general and lighting devices in particular must have an EU Energy Label clearly displayed when offered for sale or rent. The energy efficiency of the appliance is rated in terms of a set of energy efficiency classes from A to G on the label, A being the most energy efficient, G the least efficient. The labels also give other useful information to the customer. The information should also be given in catalogues and included by internet retailers on their websites. However although the Energy Label may predict behaviour of the lighting device, it may still be difficult to monitor the behaviour of the lighting devices during actual operation. SUMMARY OF THE INVENTION

In view of the above, the inventors of the present invention have realized that parameters relating to the electronic appliances change over time. The parameters may change due to fatigue of mechanical, electrical and/or optical components of the electronic appliances, use of the electronic appliances, dirt accumulated in or on the electronic appliances, and the like. Therefore energy labels may not provide accurate information regarding power consumption and/or lumen output thus making lighting devices difficult to be monitored.

It is an object of the present invention to overcome this problem, and to provide an improved lighting device arranged to provide an indication of power consumption and/or lumen output.

Generally, the above objectives are achieved by a lighting device according to the attached independent claim. According to a first aspect of the invention, this and other objects are achieved by a lighting device comprising a light emitting element; a light sensor arranged to sense a lumen contribution of light emitted by the light emitting element; an estimator arranged to estimate a relation between the sensed lumen contribution and the sensed power consumption; and an indicator arranged to receive the estimated relation from the estimator, and to output an indication of the estimated relation.

Advantageously such a lighting device provides an indication of the power consumption and/or lumen output (of the light emitting element) but also power consumption of the driver and the total consumption. The power sensor may be arranged to sense power consumed by the light emitting element only or it may be arranged to sense the total power consumed by the lighting device by also sensing the power consumed by the driver of the light emitting element. Thereby the power consumed by the light emitting element may be compared to the power consumed by the entire lighting device, thereby providing an indication of the efficiency of the light emitting element.

According to an embodiment the lighting device further comprises a comparator arranged to relate the estimated relation to a predetermined relation between lumen contribution and power consumption and to provide the indicator with the related relation. Thereby the estimated relation may be bounded within a predetermined interval, thereby avoiding overflow and/or underflow of the estimated relation. This may improve indication of the estimated relation.

According to an embodiment the lighting device further comprises a communications interface arranged to receive the predetermined relation. Thus the indicator can provide a signal which can be directly detected by a human and/or the signal could be sent remotely to a central location. Thereby the predetermined relation may be updated.

According to an embodiment the light sensor is placed remotely from the light emitting element. Thereby the lumen output may be estimated at a predetermined location at which the light of the lighting device is intended to be used. This light sensor may be located outside the light emitting element but still close to this light emitting element in order to minimize influence of surrounding objects and/or other light. With LED sources it is possible to superimpose a unique modulated light signal to the emitted light by which influence of the emitted light and the surrounding light can be separated.

According to an embodiment the light sensor comprises a photodiode arranged to estimate the light emitted by the light emitting element. Such a photodiode may improve accuracy of the estimated light.

According to an embodiment the lighting device further comprises a controller arranged to control the power consumed by the light emitting element. The controller may facilitate improved control of the lighting device.

According to an embodiment the lighting device may further comprise photo feedback circuitry coupled to the light sensor and to the controller. The photo feedback circuitry may enable the light emitting element to be operated at substantially constant lumen output.

According to an embodiment the controller is coupled to the power sensor.

The power sensor may enable the light emitting element to be operated at a substantially constant power level. Whether a constant power level or a constant light level is preferred could be set externally if device can be controlled remotely.

According to an embodiment the lighting device may further comprise a temperature sensor coupled to the power sensor and arranged to sense a temperature of the light emitting element. Thereby the sensed power may be estimated from the sensed temperature, thus improving accuracy of the sensed power.

According to an embodiment the lighting device further comprises a heat sink coupled to the light emitting element. The temperature may be measured from the heat sink, thus improving accuracy of the sensed temperature.

Generally, the above objectives are achieved by a luminaire according to the attached independent claim. According to a second aspect of the invention, this and other objects are achieved by luminaire comprising at least one lighting device as disclosed above. According to an embodiment, the luminaire further comprises a housing. The indicator may be integrated in the housing.

It is noted that the invention relates to all possible combinations of features recited in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

This and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing embodiment(s) of the invention.

Fig. 1 illustrates a lighting device according to an embodiment;

Figs. 2(a)-2(b) illustrate a lighting device according to embodiments; and

Figs. 3(a)-3(d) illustrates a luminaire according to embodiments.

DETAILED DESCRIPTION

The below embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. For example, the various concepts discussed herein may be suitably implemented in a variety of lighting devices and luminaires having different form factors and light output. Like numbers refer to like elements throughout.

Fig. 1 illustrates a lighting device 102 according to an embodiment. The term "lighting device" means a device that is used for providing light in an indoor or outdoor space, for purpose of illuminating objects in the indoor or outdoor space. An indoor space is in this context typically an enclosed space, such as an apartment room, an office room, a gym hall, a room in a public place, etc. An outdoor space is in this context typically a non- enclosed space, such as part of an outdoor environment, a park, a part of a street, etc.

The lighting device 102 of Fig. 1 comprises a light emitting element 104. In general the lighting device 102 may comprise more than one light emitting element 104. Examples of light emitting elements are LEDs, incandescent filaments in light bulbs, (coating of) fluorescent lamps, etc. The light emitting element 104 is thus arranged to emit light having a certain flux. The SI unit for light flux is denoted lumen (lm). The energy efficiency, or the efficacy in lumen per watt (lm/W), is a distinguishing feature of a luminaire (or a combination of the lighting device and the luminaire) that is becoming increasingly important. By improving the energy efficiency of a luminaire and/or lighting device the energy costs may be reduced and the C0 ₂ emission may be reduced. Hence, management of energy efficiency of a luminaire has both economical aspects as well as environmental aspects.

In general, compared to other lighting devices, LED based lighting devices, or luminaires, have a long lifetime, but show a continuous drop in lumen output over lifetime. Therefore the efficiency or efficacy energy consumption of the lighting devices decreases with time, which limits the economic lifetime of the lighting devices. Energy consumption only increases if the light level is kept constant. Efficiency or efficacy will always decrease for all situations (e.g. constant light, power, and the like). However, because the lighting devices are still operable, it is difficult to judge the performance of the lighting devices without actually measuring it. As will be further disclosed below, other causes for efficiency deterioration are dust and dirt in the optical system of the lighting device. In general, lighting devices have to be cleaned on a regular basis in order to have a good performance.

The lighting device 102 therefore further comprises a light sensor 106. The light sensor 106 is arranged to sense a lumen contribution of light emitted by the light emitting element 104. That is, the light sensor 106 senses a certain light flux of the light emitted by the light sensor 106. Further, although the light flux in lumen may be the same, the colour temperature of the light emitted by the light emitting element may change due to temperature, aging effects. The light sensor may therefore be arranged to sense the colour temperature as well as the lumen contribution. Generally, the light sensor may comprise any suitable light detector arranged to estimate the light emitted by the light emitting element of the lighting device. In particular the light detector may be a photo detector, such as a photodiode. Photodiodes are capable of converting sensed light (lumen contribution and/or colour temperature) into either current or voltage, depending upon the mode of operation. The light sensor 106 may comprise an LED. An LED can be used as a photodiode for light detection as well as for light emission. Alternatively the light sensor 106 may comprise photo resistors or light dependent resistors (LDR) which change resistance according to sensed light intensity. Yet alternatively the light sensor 106 may comprise photovoltaic cells or solar cells which produce a voltage and supply an electric current when illuminated. Thus, upon sensing a light flux of the light emitting element 104 the light sensor 106 converts the sensed light flux into a corresponding electrical signal, wherein the electrical signal is indicative of the sensed light flux. For example, the electrical signal may be proportional to the sensed light flux. With a colour sensor containing at least 3 sensors (advantageously 4 sensors) the colour coordinates could be measured. For purposes of this disclosure, the term "colour" is used interchangeably with the term spectrum. However, the term "colour" generally is used to refer primarily to a property of radiation that is perceivable by an observer (although this usage is not intended to limit the scope of this term). Accordingly, the terms "different colours" implicitly refer to multiple spectra having different wavelength components and/or bandwidths. It also should be appreciated that the term "colour" may be used in connection with both white and non- white light. The term "colour temperature" generally is used herein in connection with white light, although this usage is not intended to limit the scope of this term. Colour temperature essentially refers to a particular colour content or shade (e.g., reddish, bluish) of white light. The colour temperature of a given radiation sample conventionally is characterized according to the temperature in degrees Kelvin (K) of a black body radiator that radiates essentially the same spectrum as the radiation sample in question.

In order to be able to emit light the light emitting element 104 is powered by a power supply. In general the power supply includes one or more printed circuit boards having power management and driver circuitry components disposed thereon for driving and controlling the light emitting element 104. The lighting device 102 further comprises a power sensor 108. The power sensor 108 is arranged to sense power consumed by the light emitting element 104. Advantageously the power sensor 108 is electrically coupled to the light emitting element 104. The power sensor 108 may sense the power consumed by the light emitting element from an operating current consumed by the light emitting element.

Alternatively the power sensor 108 may sense the power consumed by the light emitting element from an operating voltage measured across the light emitting element. The consumed power may be sensed (directly) from the light emitting element 104 and not directly from the power supply (although this is also possible). This may be advantageous in case of power leakage between the power supply and the light emitting element 104. The power

consumption of the light emitting element and the power supply may also be separately sensed and/or measured. This may be advantageous since this may enable the system to indicate (inter alia by means of the provision of a maintenance signal) that either light emitting element or power supply electronics needs repair or replacement

Fig. 2(a) illustrates a lighting device 202A according to an embodiment. The lighting device 202 A may be part of a luminaire 230. Similar to the lighting device 102 of Fig. 1 the lighting device 202A comprises a light emitting element 104, a light sensor 106, a power sensor 108, an estimator 110 and an indicator 112. A temperature sensor 224 may be provided in the lighting device 202. Such a temperature sensor enables sensing of the operating temperature of the lighting device 202. Particularly, the temperature sensor arranged to sense a temperature of the light emitting element may be coupled to the power sensor 108. Thereby the sensed power may be estimated from the sensed temperature.

Further, such a temperature sensor may facilitate control of the lighting device 202. The temperature sensor may be mounted within the light emitting element 204, or may be mounted in any other suitable position to enable determination of the temperature of the lighting device 202A in general and of the temperature of the light emitting element 204 in particular. The temperature sensor 224 may be connected to the power supply and control electronics to provide electrical connection to the temperature sensor.

In order to estimate the power consumption, it may be advantageous to consider the temperature difference between the light emitting element/lighting device/ luminaire and its surroundings instead of the absolute temperature of the light emitting element/lighting device/ luminaire. Therefore the power consumption estimate could be improved if the temperature close to the light source is compared to the temperature of the surroundings (i.e. outside) of the luminaire. Alternatively, consideration of the absolute temperature of the light emitting element/lighting device/ luminaire may be indicative of overheating of the the light emitting element/lighting device/ luminaire.

The lighting device may further comprise a heat sink 226. The heat sink 226 may be coupled to the light emitting element 204. Thereby the temperature of the light emitting element may be measured from the heat sink. Moreover, a thermal connector may be disposed between the light emitting element and the heat sink to provide thermal conductivity therebetween to facilitate heat dissipation. The temperature sensor 224 may then be mounted within an opening, or recess, in the heat sink, it may be mounted proximate to the heat sink, or it may be disposed within a recess of the thermal connector.

The lighting device 102, 202A further comprises an estimator 110. The estimator is arranged to receive a signal indicative of the sensed lumen contribution and a signal indicative of the sensed power consumption. According to embodiments the estimator 110 receives the signal indicative of the sensed lumen contribution from the light sensor and the signal indicative of the sensed power consumption from the power estimator. From the received signals the estimator 110 is able to estimate a relation between the sensed lumen contribution and the sensed power consumption. For example, the estimation may be proportional to the sensed lumen and inversely proportional to the consumed power. Thereby the estimator 110 may provide a signal indicating the amount of emitted light flux per consumed watt, thereby providing an estimation of the energy efficiency of the lighting device in general and of the light emitting element in particular. In other words the estimator may provide an estimation in lm/W for the estimated relation. The estimator 110 could estimate the relation continuously during operation, periodically during operation, or only a limited time, for example when the lighting device is switched on. Measurements and/or estimates could be obtained immediately after switching the lighting device on and/or after a certain stabilisation time by which also thermal efficiency could be determined. The stabilisation time may be dependent on the physical components of the lighting device in general and of the light emitting element in particular. The estimator may be implemented as an electrical, a mechanical or an electro-mechanical component. The functionality of the estimator may also be implemented in a controller.

The lighting device 102, 202 A further comprises an indicator 112. The indicator is arranged to receive the estimated relation from the estimator 110. Upon receiving the estimated relation the indicator 112 is able to output an indication of the estimated relation. The indicator could output an indication of the relation continuously during operation, periodically during operation, or only a limited time, for example when the lighting device is switched on. The lighting device may further comprise a comparator 216. The comparator 216 is arranged to relate the estimated relation to a predetermined relation between lumen contribution and power consumption and to provide the indicator 112 with the related relation. Thereby it may be easier to visualize the estimated relation. For example, the comparator 216 may scale the estimated relation such that it is confined within a predetermined interval. In particular the comparator 216 may subject the estimated relation to a linear or non-linear function, thereby transforming the estimated relation to, for example, a logarithmic scale or the like.

Hence, by means of the indicator 112 the estimated relation may be outputted from the lighting device 102, 202A and/or luminaire 230. A user and/or viewer of the lighting device and/or luminaire may thereby receive information, such as visual feedback, regarding the estimated relation. The liminaire 230 may comprise a housing 232, and the indicator 112 may integrated in the housing 232. For example the colour of (part of) the housing may change with the estimated relation (see below). Figs. 3(a)-3(d) illustrate luminaires 230 according to embodiments. According to embodiments the indicator 112 is part of a user interface 228. The user interface 228 may provide visual feedback regarding the energy efficiency of the lighting device 102, 202A in general and of the light emitting element 104 in particular to a user. Via the user interface 228 and/or housing 232 a user may thereby receive a signal indicating the grade of efficiency. The user interface may be provided as one or more light sources. The efficiency may be indicated by coloured indicator LEDs, small displays (e.g. LCD, OLED), or a strip containing electrochromic, photochromic, or thermochromic material. In the latter cases, the strip material could function as a light sensor and an indicator at the same time. As in Fig. 3(a) the housing 232 may be provided with one or more colour variable indicator light(s) 112A. As in Fig. 3(b) the housing 232 may be provided with a colour variable indicator strip 112B. As in Fig. 3(c) the housing 232 may be provided with a colour variable indicator rim 112C. As in Fig. 3(d) the housing 232 may be a colour variable indicator housing 112D.

The user interface 228 and/or housing 232 may be arranged to output light in a different colour depending on the received estimated indication from the indicator. High energy efficiency may be associated with a green light; intermediate energy efficiency may be associated with an orange light; and low energy efficiency may be associated with a red light. In this context high energy efficiency may be considered as about 100%-70% of initial efficiency of the light emitting element; intermediate energy efficiency may be considered as about 75%-50% of initial efficiency; and low energy efficiency may be considered as about 50%-0% of initial efficiency. Different definitions of high, intermediate and low energy efficiency also falls within the scope of the present invention. For example, lifetime of a light emitting element is usually defined as 50% of initial flux. Also end-of-(economic)-life aspects may be considered. The lighting device may further comprise a communications interface 218 arranged to receive the above disclosed predetermined relation. Further, in order to facilitate updating of the efficiency intervals the communications interface 218 of the lighting device or luminaire may be arranged to receive updated efficiency intervals. The lighting device or luminaire may further be provided with control means for updating the efficiency intervals based on the received updated efficiency intervals. Thereby an indicator displaying e.g. the colour (red-orange-green) according norms of a particular time and place may be enabled.

Likewise, different ways of providing indications of high, intermediate and low energy efficiency also falls within the scope of the present invention. For example an intermediate efficiency indication it may be advantageous to replace the light emitting element and/or lighting device. For example, if transforming to an indication of a low efficiency, a signal could be sent to an external device, such as a computer, to make responsible maintenance person aware that it may be necessity to replace light emitting element and/or lighting device. The signal may indicate the efficiency of the light emitting element and/or lighting device as well as, for example, an internet protocol (IP) address of the lighting device.

The lighting device may further comprise a controller 222. The term

"controller" is used herein generally to describe various apparatus relating to the operation of one or more light sources. A controller 222 can be implemented in numerous ways (e.g., such as with dedicated hardware) to perform various functions discussed herein. A "processor" is one example of a controller which employs one or more microprocessors that may be programmed using software (e.g., microcode) to perform various functions discussed herein. A controller 222 may be implemented with or without employing a processor, and also may be implemented as a combination of dedicated hardware to perform some functions and a processor (e.g., one or more programmed microprocessors and associated circuitry) to perform other functions. Examples of controller components that may be employed in various embodiments of the present disclosure include, but are not limited to, conventional microprocessors, application specific integrated circuits (ASICs), and field-programmable gate arrays (FPGAs). The controller may be arranged to control the power consumed by the light emitting element.

The lighting device 202A may further comprising photo feedback circuitry. According to embodiments the photo feedback circuitry is coupled to the light sensor 106 and to the controller 222. Hence the controller 222 may receive an indication of the sensed light. Upon receiving the indication the controller 222 may compare the indication to one or more predetermined levels of light flux. As a result of, e.g., such a comparison the controller may, for example via the power supply, adapt the power supplied to the light emitting element 104 such that it reflects a desired level of light flux. For example, if the sensed light flux is below a desired level the supplied power may be increased, thereby increasing the light flux of the light emitting element, and vice versa. Hence the photo feedback circuitry may enable the light emitting element to be operated at substantially constant lumen output.

By receiving feedback from, for example, the power supply the controller 222 may enable the light emitting element 104 to be operated at a substantially constant power level. In this context the term "substantially" should be interpreted as a power level which does not deviate from a constant level more than a pre-determined amount. The

predetermined amount may be a fixed percentage, such as 15%, 10% or 5% above and/or below the constant power level.

When considering constant lumen a guaranteed lighting level (e.g. currently applied in some systems for outdoor lighting of roads) may be maintained; when considering constant power power consumption regulations (like the office building norms for power consumption) may be fulfilled. A combination of the two considerations is also imaginable: ensure a constant lumen output until a given maximum power norm is reached and then switch to constant power.

The lighting device 102, 202A may further comprise a front cover element 214. The front cover element, or lens, is usually of a clear transparent material, such as glass, acrylic, or polycarbonate. It should be noted that the term "cover element" may be integrated with the light emitting element 104. In this respect the glass cover of an incandescent light bulb or fluorescent light tubes may be regarded as such a cover element. As noted above, the front element may be subject to dirt, wear and tear, or other types of fatigue. For example, as a result of the light emitting element burning, the cover element 214 may darken.

Influence of dirt could be determined by specifying type of room which indirectly corresponds to a certain degree of flux over life time or as such it can be measured with same sensor for relative flux output if sensor is positioned in a clever way. Fig. 2(b) illustrates a lighting device 202B according to an embodiment. The lighting device 202B may be part of a luminaire 230. Similar to the lighting device 102 of Fig. 1 and the lighting device 202A of Fig. 2(a) the lighting device 202B comprises a light emitting element 104, a power sensor 108, an estimator 110 and an indicator 112. The lighting device 202B further comprises a first light sensor 106 A and a second light sensor 106B. In more detail, the first light sensor 106A may be placed inside the luminaire (and close to actual light emitting element), the flux of initial light source is measured; the second light sensor 106B may be placed outside the luminaire thereby estimating and/or measuring the light outside the luminaire. Relative light flux of the light emitting element may thereby be monitored. A ratio between the signals from the first and second light sensor, respectively, gives an indication of dirt, yellowing cover, loss of reflectivity or impact of optical efficiency of the optical system. Typical degradation caused by dirt is known is, for typical rooms, known in the art. Thereby the effect of dirt during the operational life cycle of the luminaire can be roughly predicted. However, actual measuring with two light sensors may be much more reliable. Using two light sensors may also be indicative not only of dirt but also of the total degradation of the optical system of the luminaire.

The indication of the efficiency may depend on maintenance of the lighting device, on dirt on the light emitting element but also on dirt on the lighting device because the front cover element 214 itself also becomes dirty. Hence by placing the light sensor 106 inside or outside the cover element 214 different aspects of fatigue may be identified. If the light sensor is placed outside the cover element (in view of the light emitting element) a dirty cover element may be detected. Similarly, if the light sensor is placed inside the cover element (in view of the light emitting element 104) a weak light emitting element may be detected. The remedy to improve the light flux is different for these two cases; according to the first scenario the light flux may be improved if the cover element 214 is cleaned, whereas according to the second scenario the light flux may be improved if the light emitting element 104 is replaced.

The light sensor 106 may be placed remotely from the light emitting element. In this context the term "remotely from" should be interpreted as having the meaning that the light sensor 106 is placed distant from the lighting device 102 but still being operatively connected to the lighting device 102 and thereby still being part of the lighting device 102. Such a remote placing of the light sensor may be advantageous if the light flux at a certain location is to be sensed. As the distance between the light sensor and the light emitting element increases the light flux sensed by the light sensor may also be influenced by light emanated from light sources. The amount of influence from such other light sources may be reduced by having a light sensor which is sensitive in a certain direction. Alternatively, in case the total light contribution (i.e. the light contribution from the lighting device 102 as well as the light contribution from other light sources) is of interest the light sensor may be omnidirectional. Thus only one lighting device of a group of lighting devices has to be equipped with such a light sensor. For a closed lighting device fixture, like streetlight fixtures, the position of the light sensor could be at another location.

In summary, the lighting device is provided with means (a power sensor and a light sensor, respectively) to sense the consumed power and/or the lumen output. In case the lighting device is used at constant power, the outputted light flux could be monitored (e.g. with a photodiode). In case the lighting device is operated at constant light flux output (e.g. by using photo feedback), it may be sufficient to monitor only the power consumption. The efficiency could be monitored directly (by measuring current, voltage, light flux output) or indirectly by measuring the temperature of the light emitting element or of a heat sink coupled to the light emitting element.

The light emitting elements may be integrated with other components in the form of a luminaire or other general purpose lighting structure. Thus, in general the lighting device may be part of a luminaire. Typically such a luminaire may comprise one or more lighting devices as disclosed above. 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.