LUMINAIRE SYSTEM AND METHOD FOR DETERMINING WATER INGRESS INTO A LUMINAIRE

Abstract

The invention relates to a luminaire system (100) comprising a lighting unit (101), a housing (102) containing at least a part of the lighting unit, wherein the lighting unit and the housing are parts of a luminaire, and a sensing means (103) positioned at or within the housing, wherein the sensing means is adapted to sense a functional parameter indicative of a functional characteristic of the luminaire that is influenced by water ingress into at least a part of the luminaire. Further, the luminaire system comprises a water ingress determination unit (104) being adapted to determine water ingress into at least a part of the luminaire based on the sensed functional parameter. Thus, a luminaire system is provided that allows to determine water ingress into a luminaire before the water can damage the luminaire such that the persistence and safety of the luminaire is improved.

Claims

1. A luminaire system comprising: a lighting unit being adapted to provide light, a housing containing at least a part of the lighting unit, wherein the lighting unit and the housing are parts of a luminaire, a sensing means positioned at or within the housing adapted to sense a functional parameter indicative of a functional characteristic of the luminaire that is influenced by water ingress into at least a part of an inner structure of the luminaire, wherein the functional characteristic refers to a characteristic of the luminaire that is functionally related to a function of the luminaire; wherein the functional parameter is indicative of a pressure within at least a part of the housing of the luminaire and/or of a temperature of the luminaire; and a water ingress determination unit being adapted to determine water ingress into at least a part of the inner structure of the luminaire based on the sensed functional parameter; wherein the water ingress determination unit is further adapted to utilize a functional relation between an amount of water and/or water vapor present in the inner structure of the luminaire and the functional parameter.

2. The luminaire system according to claim 1, wherein the water ingress determination unit is adapted to determine the water ingress into at least a part of an inner structure of the luminaire by comparing a sensed functional parameter with a predetermined baseline of this parameter.

3. The luminaire system according to claim 2, wherein the baseline of the functional parameter is predetermined based on a parameter model that is adapted to model the functional parameter of the lighting unit with respect to an ambient environmental condition and/or an operational and/or a water ingress state of the lighting unit.

4. The luminaire system according to claim 1, wherein the sensing means is adapted to sense the functional parameter of the luminaire at different operational states of the lighting unit and wherein the water ingress determination unit is adapted to determine water ingress into at least a part of an inner structure of the luminaire based on a comparison of the functional parameters determined at different operational states of the lighting unit.

5. (canceled)

6. The luminaire system according to claim 1, wherein the sensing means is positioned at the housing of the luminaire and is adapted to sense as functional parameter being indicative of a pressure within at least a part of the housing, of the luminaire a deformation of at least a part of the housing.

7. The luminaire system according to claim 6, wherein the housing comprises at least a flexible part and a rigid part, wherein the flexible part is more flexible than the rigid part, and wherein the sensing means is adapted to sense a deformation of the housing by sensing the deformation of the flexible part of the housing.

8. The luminaire system according to claim 1, wherein the sensing means is adapted to sense as functional parameter being indicative of a pressure within at least a part of the housing of the luminaire a mechanical force applied to at least a part of the housing.

9. (canceled)

10. The luminaire system according to claim 1, wherein the functional parameter being indicative of a temperature of the luminaire refers to a temperature profile measured during a change of the lighting unit from one operational state to another.

11. The luminaire system according to claim 1, wherein a further sensing means is provided that is adapted to sense a humidity parameter indicative of a humidity within at least a part of the housing of the luminaire, wherein the water ingress determination unit is adapted to determine water ingress into at least a part of an inner structure of the luminaire further based on the humidity parameter.

12. The luminaire system according to claim 1, wherein the housing comprises a sinkhole provided such that water present in the housing will accumulate in the sinkhole, wherein a further sensing means is adapted to sense the presence of water in the sinkhole.

13. A luminaire system according to claim 1 further comprising a functional parameter providing unit adapted to provide a functional parameter with respect to another luminaire being part of the luminaire system or being external to the luminaire system, wherein the water ingress determination unit is adapted to receive the provided functional parameter and to determine water ingress into at least a part of the inner structure of the luminaire further based on the provided functional parameter.

14. A method for determining water ingress into at least a part of an inner structure of a luminaire, wherein the method comprises: providing measurements of a functional parameter of a luminaire comprising a lighting unit and a housing containing at least a part of the lighting unit, wherein the functional parameter is indicative of a functional characteristic of the luminaire that is influenced by water ingress into at least a part of an inner structure of the luminaire, wherein the functional characteristic refers to a characteristic of the luminaire that is functionally related to a function of the luminaire; wherein the functional parameter is indicative of a pressure within at least a part of the housing of the luminaire and/or of a temperature of the luminaire; and determining water ingress into at least a part of the inner structure of the luminaire based on the sensed functional parameter; wherein the water ingress determination unit is further adapted to utilize a functional relation between an amount of water and/or water vapor present in the inner structure of the luminaire and the functional parameter.

15. A computer program product for determining water ingress into a luminaire, wherein the computer program product comprises program code means causing a computer to execute the method according to claim 14.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In the following drawings:

[0049] FIG. 1 shows schematically and exemplarily a luminaire system,

[0050] FIG. 2 shows schematically and exemplarily a method for determining water ingress into a luminaire,

[0051] FIGS. 3A-3C, 4A-4C and 5 show schematically and exemplarily aspects of preferred embodiments of the invention,

[0052] FIG. 6 shows schematically and exemplarily a graph illustrating principles of an embodiment for determining water ingress into the luminaire, and

[0053] FIGS. 7A and 7B show schematically and exemplarily an aspect of another preferred embodiment of the invention comprising a moisture holding substrate.

DETAILED DESCRIPTION OF EMBODIMENTS

[0054] FIG. 1 shows schematically and exemplarily a luminaire system 100 with an improved persistence and safety. The luminaire system 100 comprises a lighting unit 101 for providing light 107. The lighting unit 101 can comprise, for instance, an LED and circuitry for controlling the LED and for providing power to the LED. However, the lighting unit 101 can also comprise any other light source that can provide light 107. Optionally, the lighting unit 101 comprises also a controlling unit realized, for instance, as dedicated hardware or as software running on a general computation device, wherein the controlling unit is adapted to control the lighting unit 101, in particular, to control the light 107 provided by the lighting unit 101. However, the control unit can also be adapted to control other functionalities of the lighting unit 101, if provided by the lighting unit 101.

[0055] Further, the luminaire system 100 comprises a housing 102 encompassing in this example the LED and at least a part of a circuitry provided together with the LED as part of the lighting unit 101. Preferably, the housing 102 comprises a transparent part, for instance, a dome shaped part shown in FIG. 1, and a non-transparent part, for instance, the part below the lighting unit 101 shown in FIG. 1, which can be regarded as a construction basis to which the lighting unit 101 can be attached and that provides stability to a luminaire formed at least by the lighting unit and the housing. Generally, the housing 102 can take a wide variety of forms and designs that are determined and selected based on the intended application of the luminaire and the fixing system chosen for the respective luminaire. Further, the luminaire system 100, in particular, the luminaire defined by the lighting unit 101 and the housing 102, comprises at least a sensing means 103, wherein the sensing means 103 is adapted to sense a functional parameter indicative of a functional characteristic of the luminaire that is influenced by water ingress into an inner structure of the luminaire, for instance, into the housing 102 of the luminaire and/or into the circuitry of the lighting unit 101. A functional parameter measured by the sensing means 103 can refer to any parameter that allows to infer the influence of water ingress onto a functional characteristic of the luminaire. For example, the functional parameter can refer to a temperature measured within the housing 102 of the luminaire, wherein changes in the measurement of the temperature as provided by the sensing means 103 as functional parameter can be indicative of water that has ingressed into the housing 102 of the luminaire. However, also other functional parameters can be measured by the sensing means 103, for instance, parameters like a pressure within the housing 102 of the luminaire, a deformation of the housing 102 of the luminaire, etc. The sensing means 103 can then be realized in accordance with the functional parameter that should be measured by the sensing means 103. For example, if the functional parameter is selected to refer to a temperature within the housing 102, the sensing means 103 can be embodied by any known temperature sensor, for instance a thermocouple. Moreover, if a pressure should be detected as functional characteristic of the luminaire, the sensing means 103 can be embodied by any pressure sensor, for instance, by a piezoelectric sensor, that allows to determine the pressure, or pressure differences within the housing 102.

[0056] The luminaire system 100 comprises further a water ingress determination unit 104 which can be realized as dedicated hardware or as software running on a general computation system. The water ingress determination unit 104 can be provided as part of the luminaire, for instance, incorporated into a circuit board that is also utilized for providing circuitry for controlling the lighting unit 101 of the luminaire. However, the water ingress determination unit 104 can also be provided outside of the luminaire, in particular, on a different device, like a user device. In a preferred embodiment, the water ingress determination unit 104 is realized as a software application running on a user computation system like a smart phone, a server, a laptop, etc. Generally, the water ingress determination unit 104 is adapted such that it can receive the functional parameters sensed by the sensing means 103 of the luminaire system 100. For example, the water ingress determination unit 104 can directly be connected with the sensing means 103, for instance, via a wired connection provided on a circuit board, or via a wireless connection between the sensing means 103 and the water ingress determination unit 104, or via a non-direct connection utilizing an intermediate system, like a server to which the luminaire provides the functional parameters measured by the sensing means 103, a storage in which the sensed functional parameters are already stored, a gateway connecting the sensing means 103 with the water ingress determination unit 104, etc. Optionally, the water ingress determination unit 104 can further comprise an input unit 105 such as the keyboard, a switch, a contact sensor, etc. and/or an output unit 106 such as a display, light output system, audio output system, etc.

[0057] The water ingress determination unit 104 is adapted to determine the water ingress into at least a part of the inner structure of the luminaire based on one or more sensed functional parameters. For example, the water ingress determination unit 104 can utilize a functional relation between a sensed functional parameter and an amount of water present in at least a part of the inner structure of the luminaire, for example, present in the housing 102. Such a functional relationship can be provided to the water ingress determination unit 104 from a storage storing the functional relation. Generally, such a functional relation can be determined based on experiments performed, for instance, at a construction site with luminaires of the same type. In this context, a plurality of functional parameters of the luminaire can be measured with different amounts of water present within the housing 102 of the luminaire. From such measurements a functional relation can then be determined with known statistical methods and can be provided, for instance, in form of a mathematical relationship, a look-up table, or a set of rules that can be applied by the water ingress determination unit 104 to the functional parameters measured by the sensing means 103.

[0058] The result of the water ingress determination of the water ingress determination unit 104 can refer, for instance, to determining an absolute or relative amount of water present within at least a part of the luminaire. However, the result can also be a simple determination on whether water is present inside at least a part of the luminaire or not. The result of the water ingress determination can then be provided by the water ingress determination unit 104 to a user, for instance, by utilizing the output unit 106 and can refer, for instance, to a visible or audible output indicating that water is ingressed into the luminaire. Moreover, the output can also refer to providing additional information with respect to the determined water ingress, like an estimate on how seriously functions of the luminaire might be affected by the water ingress, whether or not a user should contact an installer for fixing or exchanging the luminaire or parts of the luminaire, etc. Additionally or alternatively, the water ingress determination unit 104 can also be adapted to provide the result of the water ingress determination to the luminaire itself, for instance, via a wired or a wireless communication with the luminaire such that a controller of the luminaire, in particular, a controller of the lighting unit 101, can utilize the results of the water ingress determination to control the luminaire, in particular, the lighting unit 101 of the luminaire. For example, if the water ingress determination unit 104 determines as result of the water ingress determination that the amount of water present in the inner structure of the luminaire might provide a safety risk, for instance, due to the possibility of occurring short-circuits, this information can be utilized by a controller of the luminaire for causing a switching off of a power supply of the luminaire. In an embodiment, a water ingress determination result can also be utilized by a controller for controlling the lighting unit 101 based on the water ingress determination result. For example, the controller can be configured to adapt, i.e. increase or decrease, a light intensity of the light 107 provided by the lighting unit 101 based on the water ingress determination result. Moreover, a controlling of the lighting unit 101, for instance, by a controller, can also be utilized to indicate the water ingress determination result to a user, for instance, by changing a color of the light 107 provided by the lighting unit 101, by providing a kind of blinking pattern of the light 107 provided by the lighting unit 101, etc., at certain times, for instance, shortly after switching on the lighting unit 101.

[0059] FIG. 2 shows schematically and exemplarily a method for determining water ingress into a luminaire. The method 200 comprises a first step 210 of providing measurements of a functional parameter of a luminaire, for instance, the luminaire as described with respect to FIG. 1. The measurements can be provided, for example, by the sensing means 103 of the luminaire. However, the measurements can also be provided by a measurement providing unit that can be realized, for instance, as a storing unit storing the measurements of the sensing means 103. Further, the method comprises a step 220 of determining water ingress into at least a part of the inner structure of the luminaire based on the sensed functional parameter, for instance, utilizing a water ingress determination unit 104 as described above. Optionally, the method 200 can further comprise a step of providing the results of the water ingress determination to a user, for instance, utilizing the lighting unit 101 of the luminaire or an output unit 106 of the water ingress determination unit 104. Additionally or alternatively, the method can also comprise a step of controlling the lighting unit 101 of the luminaire based on the results of the water ingress determination utilizing, for instance, a controller of the lighting unit 101.

[0060] In the following, some preferred embodiments will be described in more detail. In a preferred embodiment, the sensing means 103 is adapted to monitor as functional parameter a deformation of the luminaire housing 102 caused by humidity-induced increased pressure differentials. Generally, a sealing of a luminaire, for instance, a housing 102, strongly reduces the ability of the luminaire to reduce pressure fluctuations in a fast manner, both for positive fluctuations, i.e. over pressure, and negative fluctuations, i.e. vacuum. It is generally known that pressure differentials occur when a luminaire turns on and off. Moreover, it is also generally known that such pressure differential can be utilized to determine whether a sealed luminaire is able to hold a pressure differential which can be an indicator for the existence of a leak path to the outside environment.

[0061] In this context, it can be observed that also water ingress modifies the general pressure fluctuation behavior of a luminaire independent on the presents of a leak path. Thus, it is preferred that the sensing means 103 in one embodiment is adapted to provide as functional parameter a pressure profile, more preferably a pressure-differential profile, i.e. a profile of the pressure difference between an inside of the luminaire, for example, of the housing 102, and the outside of the luminaire, resulting from monitoring a pressure within the luminaire, for example, within the housing 102 over a time period, preferably over 24 hours. The water ingress determination unit 104 is then adapted to compare the pressure profile with a baseline pressure profile determined when no water is present in the inner structure of the luminaire, for instance, determined directly after an installation of the luminaire. Based on this comparison, in particular, based on differences between the two profiles, the water ingress determination unit 104 can then be adapted to determine if water ingress has occurred, i.e. if water is present in the luminaire.

[0062] In an embodiment, the sensing means 103 is adapted to provide as functional parameter a pressure profile of a luminaire without actually measuring the pressure. FIGS. 3A-3C shows an embodiment, in which the sensing means 103 refers to a strain gauge 302 placed on a luminaire surface 301 of the housing 102 as shown in FIG. 3A without deformation. Utilizing the deformation of the strain gauge 302 as shown schematically in FIGS. 3B and 3C for a positive and negative deformation, a deformation of the luminaire housing 102 due to a pressure differential to the outside environment can be measured. As shown in FIGS. 3A-3C the strain gauge 302 as sensing means is preferably provided with a strain sensitive pattern of an electrical conductor 304 provided with terminals 303 at the end of the conductor 304 at which the electrical properties of the conductor 304 can be determined. As shown in FIG. 3B, a deformation of the housing 102 resulting in a tension leads to an elongation of the strain gauge 302 and therefore to a narrowing of the conductor 304′ and thus to an increase of an electrical resistance at the terminals 303, whereas, as shown in FIG. 3C a deformation resulting in a compression leads to a shortening of the strain gauge 302 and therefore to a thickening of the conductor 304″ and thus to a decrease of the electrical resistance at the terminals 303. Therefore, a strain gauge 302 provides an easy and simple possibility to measure a pressure differential between the inside of the luminaire and an outside of the luminaire.

[0063] In a preferred embodiment, a part of the luminaire housing 102 is provided to be more flexible than the rest of the housing 102 to enhance the deformation due to pressure differentials. The sensing means 103 can then be placed on the surface of the more flexible part, i.e. this deformable luminaire part, for instance, in form of copper tracks acting as a simple strain gauge.

[0064] The sensing means 103 can in this example also be provided in form of a MEMS pressure sensor as shown in FIGS. 4A-4C. In this example, piezoresistive sensors 412 constructed in accordance with the strain gauge principles are applied at edges between the more flexible part 411 and the rest of the housing 410. Preferably, for a MEMS sensor the more flexible part 411 refers to a thin silicon membrane that upon a deformation 420 changes the piezo-resistance of piezoresistive sensors 412 at the edges of the flexible part 411.

[0065] As alternative to strain gauges, also piezo resistors can be utilized as sensing means 103 in order to measure mechanical forces on a certain luminaire housing part due to the pressure differential with the exterior environment. A piezo resistor passively generates a voltage dependent on the degree of mechanical deformation it experiences.

[0066] FIG. 5 shows an embodiment of a typical watertight luminaire housing 500. In watertight luminaire housings, typically a flexible rubber seal 510 is provided between different parts of the housing 530, 520 and used to make the housing watertight. In this embodiment, a part of the rubber seal 510 can be provided with the sensing means 103, for instance, in form of a piezo resistor. Due to the generally flexible nature of the rubber seal 510, if there is a positive pressure differential to the outside environment, the rubber seal 510 will be mechanically expanded in direction of the two parts of the housing 530, 520, wherein this expansion can then be measured by the sensing means 103. In a specific embodiment, the sensing means 103, for instance, in form of a piezo resistor, can be placed in direct contact with the rubber seal 510 and thus be adapted to measure the expansion of the seal, wherein then the degree of the expansion of the rubber seal 510 is indicative of the pressure differential between the inside of the luminaire and the outside. In another specific embodiment, the downwards force on the luminaire cover, i.e. seal, shown in see FIG. 5 can be measured as functional parameter. For instance, if the external pressure on the luminaire is higher than the internal pressure within the luminaire, this leads to a force on the luminaire cover 530, i.e. the upper housing part. The sensing means 103 can then be adapted to monitor as functional parameter this force, wherein the sensing means 103 can be a piezo resistor that is placed directly underneath the rubber seal 510, i.e. in between the rubber seal 510 and a part of the housing, for example, the lower housing part 520. Additionally or alternatively, an additional mechanical part, for example, a pole, can be positioned vertically between the upper housing part 530 and lower housing part 520. If the pressure on the housing or on the parts of the housing, increases, the sensing means 103, for example, a piezo resistor, located underneath this pole, i.e. between the pole and a part of the housing 530, 520, can be adapted to detect the presence of a substantial pressure differential. Based on these measurements the water ingress determination unit 104 can then be adapted inferring water ingress.

[0067] In an embodiment, the development of the pressure differential over time inside and outside at least a part of the housing is measured. A pressure differential can be caused by environmental changes as, for instance, temperature changes of the ambient temperature by sun light such that for a closed housing a baseline pressure differential can be recorded with a specific shape. Exemplarily, the baseline pressure differential comprises a daily repeated shape dependent on sun rise and sun dawn. In case of a substantially closed housing, the pressure differential is much higher in comparison to a substantially leaky housing such that water ingress originating from the leaky housing in at least a part of the housing can be determined by determining deviations of the pressure differential from the baseline pressure differential.

[0068] In an embodiment the ideal gas law can be utilized by the water ingress determination unit for determining water ingress. The ideal gas law is often written in the empirical form as:

PV=nRT,

where P, V and T are the pressure, volume and temperature, respectively, n the amount of substance, and R is the ideal gas constant. In case of a sealed luminaire, the gas volume is per definition constant while the temperature and pressure of the gas can vary. For example, after a luminaire, in particular the lighting unit, has transitioned from an on- to an off-state, the heat dissipation by the lighting unit and power circuitry stops. Hence, the luminaire's internal temperature will decrease according to a specific temperature and pressure profile, which is dependent on both the luminaire- and external environment temperature. Water ingress into the luminaire alters the temperature and pressure profiles during the change of the states of the luminaire. For instance, when a luminaire has suffered from water ingress, gas will be leaving and entering the housing during a cool down phase of the luminaire. Thus, if water is present in the fixture, i.e. the luminaire, the thermal and pressure profiles within the luminaire housing will deviate from the normal baseline profile recorded without the presence of water, for instance, during a product release of the luminaire or previously measured for this specific luminaire in the field before the water ingress event has occurred. As already described above, a pressure profile can be monitored by the sensing means in a plurality of ways, for example, by utilizing a MEMS pressure sensor. For monitoring the temperature profile the sensing means can alternatively or additionally be provided with a respective temperature sensor, for instance, a thermocouple.

[0069] It has further been observed that accumulated water or humid air within the housing of the luminaire can increase the thermal mass of the luminaire, i.e. the ability of the luminaire to adapt its temperature with respect to respective temperature stimuli. Hence, when compared to a dry luminaire baseline, the presence of water will slow the speed of temperature changes of the luminaire when, for instance, a functional state of the luminaire is changed. For example, the speed with which a luminaire adapts to a new temperature in an event of a transition between different dim-levels, i.e. dim-states, will be decreased. Thus, the presence of water can have an influence on a temperature transition profile of a luminaire.

[0070] Accordingly, in an embodiment the sensing means is adapted to measure a temperature profile, i.e. a temperature over time, as functional parameter within the luminaire. For instance, the temperature profile can be easily measured, when the sensing means refers to an embedded temperature sensor in any microcontroller located within the housing, or to a dedicated thermocouple within the luminaire. Moreover, it is preferred that both a humidity and a temperature is measured by a sensing means referring, for instance, to a single MEMS sensor. The compact dimensions of a MEMS sensor allow for a simple integration with existing electronic circuitry in the lighting unit.

[0071] FIG. 6 shows experimental results for a sealed luminaire. The diagram 600 shows thermal models of different temperature response curves as recorded by three different internal temperature sensors within a housing of the luminaire representing on/off dimming transitions 611, 612, 613 and various dimming steps 611′, 612′ 613′ of a sealed outdoor luminaire. Since the thermal models provide a very well fit of the measured temperature response curves, the original measured temperature response curves are not visible “behind” the thermal model curves. The y-axis 602 represents a temperature and the x-axis 601 represents a time. An external air temperature 610, i.e. an environment temperature, measured in the environment of the luminaires during the transitions is shown on the bottom of the diagram.

[0072] From the measured internal temperatures for each case an empirical thermal model of the luminaire's response to dim-state transitions can be created for each transition. When switching the lighting unit from an off- to an on-state, the temperature inside the luminaire will be increased by a certain temperature, because the lighting unit engine and driver dissipate heat. The temperature increases exponentially as a function of time. The same principle can be used when the inside of the luminaire cools down when switching the lighting unit off. For example, for the temperature during an on/off transition, the model can be determined from the measured temperature profile by applying the following equation and determining the respective constants of the equation from the measured temperature profile:

[00002]$T\left(t\right)=T_0+\left(T_{\mathrm{end}}-T_0\right)e^{\frac{-t}{\tau }}$

[0073] Here, T refers to the temperature, t to the time, T.sub.0 to the temperature inside the luminaire in the initial state, T.sub.end to the temperature inside the luminaire in the state to which it is switched and r to the time constant. The time it takes to reach this state of thermal equilibrium depends on the heat capacitance of the luminaire that determines the time constant τ. T.sub.end−T.sub.0 describes a certain temperature increase/decrease due to an on/off transition due to the lighting unit engine and driver dissipating heat. In case of a leaking luminaire, the actual temperature profile will deviate from the expected profile based on the thermal model. Exemplarily, for the experimental results shown in FIG. 6, the thermal model refers to:

[00003]$T_i\left(t\right)=T_{i0}+\left(T_{i,\mathrm{end}}-T_{i,0}\right)\left(1-e^{\frac{\min \left(-t,0\right)}{1100}}\right)$

[0074] Here, the index i refers to the respective measurement. The min (−t,0) operator enables for positive t to use a part of the exponential curve to model the heat up, wherein in case of a negative t the result of the model function is constant and refers to the initial temperature T.sub.0 or T.sub.i0.

[0075] As pointed out above, water ingress will change the thermal properties of the luminaire, hence the measured dynamic temperature profile recorded after the fixture, i.e. the luminaire, which has transitioned to a new dim-state will start to deviate from the modelled baseline profile measured without water ingress. Thus, the water ingress determination unit can be adapted to determine water ingress based on a comparison of a measured temperature profile during a transition between two functional states of the luminaire and the modeled baseline profile for this transition.

[0076] As demonstrated in FIG. 6, the modeled baseline temperature profiles provide an accurate fit of the temperature measured by sensing means during transitions between different luminaire dim-states. It is therefore preferred that the water ingress determination unit is adapted to apply a change detection algorithm on the temperature profile measured by the sensing means, being here a temperature sensor, to infer water ingress and/or air leakage, for instance, due to leaks in the housing. As demonstrated in FIG. 6 by three different sensor locations, for this embodiment the placement of the sensing means is non-critical and the sensing means can be provided in any location that allows to infer a temperature within the inner structure of the luminaire.

[0077] FIGS. 7A and 7B show schematically and exemplarily an aspect of another preferred embodiment of the invention comprising a moisture holding substrate. In this embodiment, the sensing means in the luminaire is a humidity sensor 700 and comprises preferably an upper electrode 701 and a lower electrode 702 which sandwich the moisture holding substrate 703. The moisture holding substrate 703 is preferably a salt or conductive plastic polymer and can be positioned with the electrodes 701, 702 on a glass substrate 704. The moisture holding substrate 703 releases ions if water vapor, i.e. water molecules of humid air, is absorbed by the moisture holding substrate 703 such that the conductivity between the electrodes 701, 702 is increased. The change of the resistance between the two electrodes 701, 702 is proportional to the relative humidity in at least a part of the housing of the luminaire. Higher relative humidity decreases the resistance between the electrodes 701, 702, while lower relative humidity increases the resistance between the electrodes 701, 702.

[0078] In an embodiment, the water ingress determination unit can be adapted to estimate an outside air-temperature based on the temperature measurements of a sensing means within the inner structure of the luminaire by utilizing the empirical thermal model. In this case, the water ingress determination unit can be adapted to determine that water is present in the inner structure of the luminaire when the estimated outdoor air temperature for the luminaire differs from a real outdoor temperature. A real outdoor temperature can be provided to the water ingress determination unit, for example, by a connection to a weather service or an averaged air temperature determined by other luminaires in the vicinity and in communication with the water ingress determination unit.

[0079] In an embodiment, the water ingress determination unit can be adapted to determine the relative humidity inside the luminaire as a function of the temperature inside the luminaire as well as the extent of the accumulated water. When the temperature increases during the day, more water may gradually evaporate, leading to a cooling effect. The accumulated water may completely evaporate. When all the water has evaporated, the humidity profile and temperature profile of the luminaire will show a distinct kink and the relative humidity will drop when the temperature inside the luminaire further increases. Based on the presence of the kink, the amount of water ingress can be inferred, e.g., moderate water ingress which evaporates during the day but returns when the temperature inside the luminaire decreases, wherein water ingress of a large amount of water significantly changes the thermal mass of the luminaire. The relative humidity also gives insights in the condensation inside the luminaire. The advantage is that leakage of the housing can be measured without needing to know the external temperature of the luminaire such that also occurrence of condensation can be measured in a closed and a leaky luminaire housing.

[0080] In an embodiment, the water ingress determination unit can be adapted to determine also minor water ingress events merely leading to some condensation. Generally, for inferring that condensation occurs inside a certain luminaire an understanding when and where the relative humidity inside the luminaire volume reaches 100% can be utilized. Condensation depends, for instance, on the temperature, the amount of water vapor present inside an inner structure of the luminaire and a resistance against water vapor diffusion from the enclosed luminaire volume towards the ambient. Temperature differentials between the inside and the outside of the luminaire can lead to cold-spot condensation within the inner structure of the luminaire. Such temperature differentials between the inside and the outside of a luminaire can be triggered by either a change of external air temperature or internal temperature within the luminaire, or both. Sometimes external temperature changes can be even dramatic, for instance, in case of a sudden thunderstorm on a hot summer day. When the temperature inside the luminaire drops rapidly, also the relative humidity in the inner structure of the luminaire will increase if the water vapor inside cannot be exchanged with the outside environment fast enough, depending, for instance, on the total volume of the housing and an ambient temperature drop, condensation inside the luminaire will occur. The condensation will then take place in areas with the lowest temperature inside the luminaire.

[0081] In an embodiment, external events leading to dramatic temperature changes (e.g. a thunderstorm) are most likely to cause condensation and hence provide a good opportunity for the proposed sensing method to assess whether a specific luminaire has accumulated water. For example, functional parameter measurements like measurements of an internal temperature, humidity and/or resistivity of a sinkhole can be recorded over a predetermined time period, for instance, over many weeks and/or months. In this case, similar external events like a series of thunderstorms can lead to similar shapes of the respective measurements of the functional parameter, whereas the similarity of the events, for instance, thunderstorms can be judged based on local weather data from another source, like the internet or additional weather sensors in the vicinity. In such a case, a change detection algorithm can be applied for detecting whether or not a change of the luminaire characteristic has occurred during the similar events and it can be derived by the water ingress determination unit when such change has occurred indicating the time of the water ingress. A change of the luminaire thermal and/or pressure behavior indicates that water ingress has occurred while previously the luminaire interior was dry. Optionally, the data of a group of identical luminaires e.g. on a street or in a city may be used for discerning whether a change has occurred in one of the luminaires.

[0082] In an embodiment, functional parameters from a large number of luminaires, preferably located in relative vicinity, are recorded and an anomaly detection algorithm can be applied to the recorded measurements. The records, i.e. the functional parameters of the other luminaires, can be stored and/or provided to the water ingress determination unit by a functional parameter providing unit. As water ingress is a rare event occurring only at a small subset of luminaires, the functional parameters of a luminaire suffering from water ingress will differ significantly from the majority of the functional parameters from the other “healthy” luminaires. Different anomaly detection techniques may be applied by the water ingress determination unit such as an unsupervised anomaly detection technique, a supervised anomaly detection technique or a semi-supervised anomaly detection technique. The unsupervised anomaly detection technique comprises detecting anomalies in an unlabeled measurement data set under the assumption that the majority of the instances in the measurement data set from the various luminaires are normal by looking for instances that seem to fit least to the remainder of the data set. The supervised anomaly detection technique comprises labeling a data set as “normal” and another data set as “abnormal” and train an algorithm to classify further data sets as “normal” or “abnormal”. The semi-supervised anomaly detection technique can comprise steps of both previously described techniques.

[0083] In an embodiment, the sensing means can additionally be adapted to measure condensed water or moisture directly. In such an embodiment the luminaire, in particular, the housing is adapted such that condensed water is collected in a sinkhole, e.g. by gravity when the humid air condenses due to low temperatures. The sinkhole is then monitored by the sensing means for presence of water. The sensing means can in this case refer, for instance, to two pads connected to an electronic circuit creating a short circuit between the two pads in the presents of water. However, instead of a sinkhole, a moisture or water holding substrate can also be provided in the luminaire. In this case the sensor means can refer to two electrodes placed in contact with the water or moisture holding substrate such that the sensing means can monitor the resistance of the water or moisture holding substrate. The water ingress determination unit can then be adapted to detect the presence of condensed water using the measurements performed by the sensing means. Moreover, the water ingress determination unit can be adapted to use the directly measured condensed water to verify a result of the water ingress determination based on the functional parameters. In particular, the water ingress determination unit can be adapted to take the results of the directly determined condensed water additionally into account when determining an amount of water in the inner structure of the luminaire based on the functional parameters. For example, functional relations between the amount of condensed water, the amount of water vapor and a functional parameter of the luminaire can be utilized by the water ingress determination unit.

[0084] Although in the above mentioned embodiments, the lighting unit comprises an LED as light source, also any other lighting unit can be used, as for instance, a halogen lamp, a fluorescent lamp, etc.

[0085] Although in the embodiment of FIG. 1, the housing of the luminaire comprises as transparent part a dome shaped part, in other embodiments of a luminaire the transparent part of the housing can be planar as, for instance, for spot lights which can be exemplarily used as in-road lights.

[0086] Although in the above mentioned embodiments often water ingress is determined in the housing of the luminaire, water ingress can also be determined in only a part of the housing, the whole housing, an inner structure of the housing, etc.

[0087] Although in the above mentioned embodiments, the luminaire system often comprises only one luminaire, a luminaire system can also comprise a plurality of luminaires. In such a case, it is preferred that a plurality of luminaires performs a task together, for instance, illuminating a way, a road, etc. or are used to guide road users in direction of, for instance, an escape or emergency exit, etc. Moreover, the luminaire system can also be adapted to communicate with other luminaire systems, for instance, as part of a network of luminaire systems. In both embodiments, it is preferred that the water ingress determination unit of a luminaire is adapted to receive functional parameters of more than one luminaire and to determine water ingress into a luminaire based on a comparison of the functional parameters of different luminaires.

[0088] Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

[0089] In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality.

[0090] A single unit or device may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0091] Procedures like the determination of the water ingress into a luminaire, the controlling of the lighting unit of the luminaire, et cetera, performed by one or several units or devices can be performed by any other number of units or devices. These procedures can be implemented as program code means of a computer program and/or as dedicated hardware.

[0092] A computer program product may be stored/distributed on a suitable medium, such as an optical storage medium or a solid-state medium, supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems.

[0093] Any reference signs in the claims should not be construed as limiting the scope.

[0094] The invention relates to a luminaire system comprising a lighting unit, a housing containing at least a part of the lighting unit, wherein the lighting unit and the housing are parts of a luminaire, and a sensing means positioned at or within the housing, wherein the sensing means is adapted to sense a functional parameter indicative of a functional characteristic of the luminaire that are influenced by water ingress into at least a part of the luminaire. Further, the luminaire system comprises a water ingress determination unit being adapted to determine water ingress into at least a part of the luminaire based on the sensed functional parameter. Thus, a luminaire system is provided that allows to determine water ingress into a luminaire before the water can damage the luminaire such that the persistence and safety of the luminaire is improved.