Method for temperature compensation of compact LED lamp

Abstract

The invention relates to a method for temperature compensation of a compact LED lamp. A method and apparatus for temperature compensation are described. The method comprises receiving (102) a target color point of light emitted by at least one light emitting device (408), determining (104) an operating power of the at least one light emitting device (408) based on a correlation of at least one temperature value of the at least one light emitting device with the received target color point, and operating (106) the at least one light emitting device (408) based on the determined operating electrical energy.

Description

Technical Field

[0001] The present invention relates to a method for temperature compensation of a lighting device, in particular to a method for temperature compensation of a light emitting diode (LED). Background Art

[0002] Today, more and more lighting tasks are performed by LED technology. This is not only due to improved energy efficiency and lower heat generation, but also due to improved brightness, smaller required installation space and improved lifespan.

[0003] For example, in modern automobiles, LED technology has been frequently used to realize headlights and taillights. Similarly, LEDs are often used to realize interior lights within the car itself, for example as signal lights. However, not only the automotive industry uses LED technology, but also other technical and engineering fields that require lighting with a given brightness and a desired color. For example, modern architecture uses the potential of LED lighting to realize daylight-adapted lighting schemes, whose color and brightness are dynamically steered in response to the daylight conditions outside the building. However, several other applications of LED technology are also envisioned.

[0004] In order to guide the brightness and color of the lighting device as desired, the lighting device may include a plurality of different light-emitting devices of different colors, which emit mixed light to produce light with desired brightness and color. Each of the plurality of light-emitting devices may also be referred to as a light-emitting component. For example, a typical lighting device may include red, green and blue LEDs, and the electrical energy supplied to the red, green and blue LEDs is adjusted so that the superposition of the light emitted by the LEDs has the desired brightness and color. However, the lighting device may also include only one light-emitting device, which may be driven in different ways to emit light of different colors and brightness, such as organic LEDs, OLEDs. In this case, a light-emitting device may include several light-emitting components, each of which is configured to emit light of different wavelengths.

[0005] Unfortunately, there is a conflict between simultaneously directing the brightness and the color of the light emitted from a lighting device. Depending on the brightness selected, the lighting device heats up in different ways and thus changes the color of the emission. For example, if the lighting device is driven in high brightness mode, it heats up more than if it is driven in low brightness mode. However, when the temperature of the lighting device changes, the color of the lighting device also changes. This effect can already be observed for conventional light bulbs, the more their filament heats up, the whiter the light they emit. Similarly, the color of an LED depends on its temperature. Therefore, if the brightness of the lighting device changes, the color of the resulting light also changes.

[0006] In order to keep the brightness and color of a lighting device stable, there is a need in the art to compensate for the effects of heat on the lighting device's corresponding light emitters. Summary of the invention

[0007] This need is met by a method and a corresponding device for temperature compensation.

[0008] The temperature compensation method according to the invention comprises receiving a target color point of light emitted by at least one light emitting device of a lighting device.

[0009] Thus, the target color point may be a certain value, such as a specific wavelength λ and / or frequency to be emitted by at least one light emitting device. It is referred to as a target color point because it is a target for at least one light emitting device to achieve a defined color under all circumstances (e.g., independent of the ambient temperature and / or the temperature of at least one light emitting device itself). Thus, any light emitted by at least one light emitting device may be characterized by its spectral radiance, i.e., by the relative distribution of radiant power as a function of the wavelength λ of the light. As is known in the art, numerous RGB color spaces may be defined, which have in common that a given perceived color is fully described by three tristimulus values ​​X, Y, and Z. The three values ​​appear because the human eye contains three types of cones (S, L, M) that may be responsible for light reception, which results in trichromatic color vision. Typical examples of RGB color spaces are CIE RGB, CIE XYZ, NTSC, and PAL / SECAM. Newer examples of RGB color spaces are DCI-P3, UHDTV, and RIMM / ROMM. Each of the three colors of the RGB color space may be given by a light emitting device. For example, one light emitting device may emit mainly wavelengths associated with red, one light emitting device may emit mainly wavelengths associated with green, and another light emitting device may emit mainly wavelengths associated with blue. The superposition of the corresponding colors then provides a perceptible color for the human eye. The three tristimulus values ​​X, Y, Z of the RGB color space describe the color of the emitted light and are obtained by integrating the spectral radiance of the emitted light over the wavelength by the corresponding curves of the three spectral sensitivity curves x(λ), y(λ) and z(λ) of the CIE standard observer. It can also be said that the tristimulus values ​​X, Y and Z of a given emitted light flux are obtained by projecting the spectral radiance of the emitted light onto each of the three spectral sensitivity curves x(λ), y(λ) and z(λ) of the CIE standard observer. In this way, each individual color state of the light emitted by the light emitting device is characterized by another three-dimensional vector of tristimulus values ​​X, Y and Z. Therefore, if a target color point is set, it can also be said that tristimulus values ​​X, Y and Z are given, which define the specific color that the light emitting device should achieve. The color tristimulus values ​​X, Y and Z are also related to the brightness, which is given as the absolute value of the vector consisting of the tristimulus values. Therefore, it can also be said that the target color point is related or associated with the target brightness. Therefore, it is also possible that the received target color point includes the brightness of the light emitted by the at least one light emitting device.

[0010] For simplicity, in the following, when RGB components (red, green and blue) are mentioned, the corresponding tristimulus values ​​X, Y and Z values ​​are also meant, and when tristimulus values ​​X, Y and Z values ​​are mentioned, the corresponding RGB components are also meant. This is because these values ​​can be converted to each other. In the following, if not explicitly stated otherwise, tristimulus values ​​X, Y and Z are equivalent to RGB colors, because tristimulus values ​​X, Y and Z can be converted into RGB colors, and RGB colors can be converted into tristimulus values ​​X, Y and Z.

[0011] or

[0012] Thus, the X value relates to the red color, the Y value represents the brightness, and the Z value relates to the blue color, and M relates to the matrix transformation between the two components.

[0013] The method for temperature compensation further comprises determining an operating power of the at least one light emitting device based on a correlation of at least one temperature value of the at least one light emitting device with the received target color point.

[0014] If a target color point is set, the electrical energy that needs to be applied to the at least one light emitting device can be determined based on the temperature of the at least one light emitting device, the mathematical correlation between the current electrical energy applied to the at least one light emitting device and the target color point. In other words, based on the knowledge of the temperature of the at least one light emitting device and the target color point, the electrical energy to be applied can be derived. The electrical energy can be quantified in the form of current and / or voltage applied to the at least one light emitting device. Therefore, the electrical energy can also be defined as the difference from the currently applied electrical energy. The currently applied electrical energy has a defined associated target color point, however, when the temperature of the at least one light emitting device changes, then the electrical energy to be applied to the at least one light emitting device also needs to be changed in order to reach or maintain the target color point. This difference in the electrical energy required to reach or maintain the target color point can be determined, and this difference can then be provided to the at least one light emitting device to operate the at least one light emitting device accordingly.

[0015] It can also be said that the known correlation between temperature, electrical energy and the color emitted or to be emitted gives a system of linear equations that can be solved for electrical energy when at least two other variables are known, namely temperature and color. One of the variables, namely color, is given by the target color point and the other variable, namely temperature, can be determined.

[0016] Thus, the temperature of the at least one light emitting device can be determined by a temperature sensor. For example, a semiconductor temperature sensor can be attached to each of the at least one light emitting device. In this case, it can be said that the temperature is measured indirectly, because heat transfer needs to occur between the at least one light emitting device and the sensor.

[0017] However, the temperature can also be determined directly. Thus, each of the at least one light emitting device can be operated in an on interval and an off interval, and thus can be operated in a time period in which more or less electrical energy is provided to each of the light emitting devices. The off interval can include at least one sensing interval, during which the electrical energy across the light emitting device can be measured, which electrical energy can then be mathematically related to the temperature of the at least one light emitting device. Typically, the temperature of the light emitting device is a function of the electrical energy provided to the at least one light emitting device. If no electrical energy is provided to the light emitting device, the temperature of the light emitting device is given by the ambient temperature. Typically, if a voltage U and a current I are applied to the light emitting device, the set power P is equal to P=U*I. The electrical energy E set in the light emitting device is equal to the integral of the power P(t) over time t. A certain small part of the set electrical energy E is dissipated in the light emitting device, and is not emitted in the form of light energy. This causes the light emitting device to heat up to a temperature T, which depends on the voltage U and the current I and other material parameters. Therefore, it can be said that the temperature T of the light emitting device is a function T(U,I), where U and I are the voltage and current applied across the light emitting device, respectively. Thus, if at least one voltage U and one current I measured across the light emitting device are given, the function T(U,I) can be used to determine at least one temperature value T. The temperature increase due to the electrical power can be called "overtemperature", which is above the ambient temperature. Therefore, the function T(U,I) and the inverse of this function will give the ambient temperature, or in the case of a temperature increase due to the electrical power, the ambient temperature plus the overtemperature dependency. In addition, any light emitting device can be characterized by a temperature-dependent resistance R(T). For example, the resistance of the filament of a light bulb increases with increasing temperature. In contrast, the resistance of a light emitting diode decreases with increasing temperature. Therefore, if the temperature-dependent resistance R(T) is given, the voltage U and the current I across the light emitting device are related by R(T)=U / I, and one of the voltage U or the current I can be substituted into the function T(U,I) to obtain the temperature T. For example, if the current I is substituted, a function T(U) of the temperature T of the light emitting device is obtained, which function T(U) is a function of the voltage U supplied across the light emitting device. If the voltage U is substituted, this results in a temperature T(I), which is a function of the current I flowing through the light emitting device. Thus, using the function T(U), a temperature value T can be determined for each of at least one measured voltage U across the light emitting device. Likewise, the function T(I) can be used to determine a temperature value T for each of at least one measured current I across the light emitting device. It can also be said that the temperature T of the light emitting device can be determined by evaluating one of the functions T(U,I), T(U) and / or T(I). Evaluating these functions can utilize numerical approximations of calibration measurements. This allows determining the temperature of at least one light emitting device in a direct manner without the need for a sensor.

[0018] The temperature determination and therefore the determination of the electrical energy that needs to be supplied to at least one light emitting device can be performed continuously, periodically or aperiodically. The frequency with which the temperature and therefore the required electrical energy are determined also depends on the expected temperature distribution of the at least one light emitting device. If the light emitting device has a more agile temperature responsiveness, the determination needs to be performed more frequently than if the light emitting device has a less agile temperature responsiveness. Agility therefore characterizes the extent to which the temperature changes over time. Agility can be determined by the heat transfer or thermal capacity of the light emitting device. A light emitting device is more agile when a greater degree of temperature change occurs in a smaller amount of time than a non-agile light emitting device. It can also be said that the light emitting devices have different energy dissipation distributions and therefore different temperature distributions. Depending on these distributions, then the temperature and the corresponding electrical energy need to be determined more frequently or less frequently in order to reach the corresponding target color point.

[0019] However, it is also contemplated that the temperature determination may be separated in time from the electrical energy determination. Thus, the temperature of at least one lighting device may be determined more frequently than the electrical energy. For example, the electrical energy required to reach the target color point may be determined only when the temperature exceeds a threshold value. The threshold value may be associated with an acceptable deviation from the target color point, so that a new determination of the electrical energy required to reach the target color point is performed only when the corresponding deviation is exceeded. However, the temperature determination may also always be combined with the electrical energy determination.

[0020] It may also be contemplated that temperature and power determinations are performed more frequently in an initial phase (eg when the light emitting device is switched on) than at a later operating time, during which the temperature of at least one light emitting device may change less frequently than in the initial phase.

[0021] The determination of the electrical energy can be performed in such a way that a target color point is reached, for example, when the at least one light emitting device is just switched on. In this case, it is necessary to determine how much electrical energy needs to be provided to the at least one light emitting device to reach the target color point. The same may also be the case if the color point itself changes. Additionally or alternatively, the determination can also be performed to maintain a given target color point, for example when the temperature changes. It is clear that the determination step can therefore be performed iteratively.

[0022] In any case, once the power required to reach or maintain the target color point is determined, the method includes operating at least one light emitting device based on the determined operating power. The operation may include providing the corresponding power to the at least one light emitting device. The operation may additionally or alternatively include controlling the power provided by the power source to the at least one light emitting device. Providing power to the at least one light emitting device may also be referred to as driving the at least one light emitting device.

[0023] Hence, by exploiting the correlation between the temperature of at least one luminous device and the color emitted by the respective luminous device at a certain power level, the influence of temperature on the color emitted by at least one luminous device may be compensated due to the adaptation of the power provided to the luminous device.

[0024] In a preferred aspect of the invention, the target color point may include tristimulus values ​​of light emitted by at least one light emitting device. The tristimulus values ​​may be given by a red portion value X, a blue portion value Z, and a brightness value Y. As already stated, the tristimulus values ​​may be associated with an RGB color space. Therefore, the target color point may also be given by RGB values. Therefore, a value may be given for the red portion of the RGB color space, a value may be given for the green portion of the RGB color space, and a value may be given for the blue portion of the RGB color space. If another quantification of color perception is used, the target color point may also include other values. In one example, the target color point may include only one value of the target wavelength λ to be emitted by the corresponding at least one light emitting device. If necessary, the method may also include converting the target color point from one color space model to another color space model.

[0025] In another preferred aspect, at least one temperature value occurs locally at the at least one light emitting device and is also directly measured at the at least one light emitting device. Locally therefore refers to the fact that the temperature is determined for the actual point where the energy dissipation results in the generation of heat. The direct measurement alleviates the need for a sensor which can only measure the heat transferred from the light emitting device to the sensor and not the direct temperature of the light emitting device. The direct measurement can be performed, for example, during at least one sensing interval during an off interval of operating the at least one light emitting device. Using the temperature value, it can then be determined the electrical energy that needs to be applied to the at least one light emitting device to maintain or reach the target color point.

[0026] In another preferred aspect, the determination further includes determining the contribution of each of the at least one light-emitting device to the received target color point. Each light-emitting device can correspond to one of the tristimulus values ​​in the RGB color space. For example, one light-emitting device can relate to the red component of the RGB color space, one light-emitting device can relate to the green component of the RGB color space, and one light-emitting device can relate to the blue component of the RGB color space. Alternatively, the red, green, and blue light components emitted from a light-emitting device can also contribute to the tristimulus values ​​in the same manner as three separate light-emitting devices. For simplicity, hereinafter, if not explicitly stated otherwise, when referring to multiple light-emitting devices that emit light of a specific color, it is also conceivable that a light-emitting device can emit a corresponding specific color with a corresponding light-emitting component.

[0027] When the light-emitting devices emit different colors (such as red, green and blue), then each of the light-emitting devices may also have a different contribution to the target color point. In order to have accurate temperature compensation, each of the light-emitting devices can be operated separately. Therefore, each light-emitting device can be independently compensated based on its own temperature and its contribution to the target color point. Therefore, it should be conceived that even if only three light-emitting devices corresponding to the corresponding RGB colors are described for exemplary purposes, it is also conceivable that several light-emitting devices correspond to the corresponding colors. As described above, it is also conceived that a light-emitting device is capable of emitting light of all three RGB colors simultaneously or intermittently, and in this case, each light-emitting component of the light-emitting device can contribute to the target color point and can be compensated accordingly. However, in this case, it is possible to consider the same temperature of all light-emitting components, at least when all light-emitting components are close enough together so that the temperature is representative of all light-emitting components. It can also be said that each of the RGB components emitted by one or more than one light-emitting device corresponds to a respective color state of the light-emitting device.

[0028] The contribution of each of the light emitting devices may depend on the respective peak power with which each of the respective light emitting devices is operated. Thus, the peak power may be the highest power over a period of time with which the light emitting devices may operate.

[0029] Furthermore, the contribution of each of the light emitting devices may be dependent on at least one temperature value of each of the respective light emitting devices.

[0030] In order to determine the operating power of each of the at least one light emitting device, the respective contribution of each of the at least one light emitting device can be stored in a lookup table as a function of the temperature value of each of the respective light emitting devices, wherein the lookup table can then be used to determine the operating power of each of the at least one light emitting device for reaching or maintaining a target color point. Thus, during an initial test phase, a setup phase, or in a laboratory, the respective contribution can be evaluated so that during normal operation of the at least one light emitting device, the respective power for reaching or maintaining a target color point can be obtained from the lookup table corresponding to the respective temperature.

[0031] In addition, the respective contribution of each of the at least one light-emitting device at a standard temperature can be stored in a vector. The vector can be used to determine the operating electrical energy of each of the at least one light-emitting device. Thus, the standard temperature can be a standardized temperature that the at least one light-emitting device may exhibit. For example, the standard temperature can be about 25°C. However, this should not be limited to this. Any temperature can be used and is used only as a reference. In addition, the temperature dependence of the contribution can be modeled by applying a corresponding relative deviation to the stored contribution at the standard temperature. Thus, each relative deviation can depend on at least one temperature value of the corresponding light-emitting device. Therefore, if the current temperature of the light-emitting device is known, the deviation from the reference temperature can be used to determine the deviation of the electrical energy that needs to be applied to the at least one light-emitting device to compensate for the corresponding temperature effect on the corresponding light-emitting device in order to reach or maintain a given target color point.

[0032] In one aspect, at least one light-emitting device includes one or several light-emitting components. If the light-emitting device includes only one light-emitting component, the light-emitting component can be configured to emit light of different wavelengths. If the light-emitting device includes several light-emitting components, each of the light-emitting components can emit light of a specific wavelength, so that the superposition of different light-emitting components produces the wavelength emitted by the light-emitting device. It should be conceived that when referring to a light-emitting device, the above two implementations are covered. The light-emitting component can be a light-emitting diode. If several light-emitting components are used in the light-emitting device, these light-emitting components can be mainly red light-emitting diodes (700nm), mainly green light-emitting diodes (546.1nm) and mainly blue light-emitting diodes (435.8nm), in which case it can also be said that the light-emitting device is an RGB light-emitting device. The light emitted from such an RGB light-emitting device is a superposition of light emitted from three different light-emitting diodes. However, each of the light-emitting components (i.e., light-emitting diodes) can also be regarded as a light-emitting device, i.e., a light-emitting device that only includes one light-emitting component.

[0033] Although various aspects of the method are described in separate paragraphs, it should be contemplated that all aspects of the method are combinable, and no aspect excludes other aspects. Thus, each of the aspects described herein can be combined individually or together with the general aspects of the described method.

[0034] The need for temperature compensation is also met by an apparatus for temperature compensation of at least one light emitting device. The apparatus comprises: a receiving unit for receiving a target color point of light emitted by the at least one light emitting device; a determining unit for determining an operating power of the at least one light emitting device based on a correlation of at least one temperature value of the at least one light emitting device with the received target color point; and an operating unit for operating the at least one light emitting device based on the determined operating power.

[0035] As mentioned above, the light emitting device may be a device that emits light of a specific wavelength. Therefore, the light emitting device may, for example, include one or several light emitting components, wherein the light emitting components may be light emitting diodes.

[0036] The receiving unit and the determining unit can be implemented by hardware or software. For example, a microcontroller can be used, which receives the target color point and easily performs the corresponding determination by adopting software.

[0037] The unit for operating at least one lighting device may be a power source which is controllable by the output of the determination unit and which provides electrical energy to the lighting device. Thus, the power source may be a voltage source or a current source.

[0038] The different units may also all be implemented together in an integrated circuit, which is employed together with or separate from at least one light emitting device.An integrated circuit (also called IC, chip or microchip) is a collection of electronic circuits on a small piece of semiconductor material. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In the following, other advantages and details of the present invention will become apparent from the detailed description of the accompanying drawings. It should be understood that none of the elements shown should be considered limiting and any software / hardware element or module that performs the corresponding described function should be covered.

[0040] Figure 1 A flow chart of the method according to the present invention is shown;

[0041] Figure 2a A schematic diagram showing light emission of a light emitting device according to the present invention at a first temperature;

[0042] Figure 2b A schematic diagram showing light emission at a second temperature of a light emitting device according to the present invention;

[0043] Figure 2c A schematic diagram showing light emission at a third temperature of a light emitting device according to the present invention;

[0044] Figure 3 A schematic diagram showing an array of light emitting devices, each light emitting device comprising three light emitting components; and

[0045] Figure 4 An exemplary block diagram of an electronic device according to the present invention is shown. DETAILED DESCRIPTION

[0046] Figure 1A method 100 for temperature compensation according to the invention is shown. The method 100 comprises the following steps: receiving 102 a target color point for light emitted by at least one light emitting device, determining 104 an operating power of the at least one light emitting device based on a correlation of at least one temperature value of the at least one light emitting device with the received target color point, and operating 106 the at least one light emitting device based on the determined operating power.

[0047] The method 100 for temperature compensation may be performed by an electronic device according to the present invention. For example, a target color point of light emitted by at least one light emitting device may be received 102 by a receiving unit of the electronic device. An operating power determination unit of the electronic device may determine 104 an operating power of the at least one light emitting device. The determination may be based on a correlation of at least one temperature value of the at least one light emitting device with the target color point received 102 from the receiving unit. The at least one temperature value may also be received from the receiving unit. The operating unit may operate 106 the at least one light emitting device based on the determined operating power.

[0048] Obviously, at least step 104 of determining the operating power of at least one light emitting device may be performed iteratively without requiring other steps to be performed as well. Thus, step 104 of determining may be performed more frequently than steps 102 and 106.

[0049] Figure 2a A schematic diagram of light emission of a light emitting device according to the present invention at a first temperature is depicted.At a given temperature and a given operating electrical energy, the light emitting device emits light of a given brightness and color.

[0050] Color is referred to herein as a photometric quantity of a light emitting device. The perceived color is fully described by three tristimulus values ​​X, Y and Z. The tristimulus values ​​X, Y, Z depend on the temperature T of the light emitting device and the operating power supplied to the light emitting device. The operating power may be given by the operating current I of the light emitting device. The dependence of the tristimulus values ​​X, Y, Z on the operating current I may be linear, whereas the dependence of the tristimulus values ​​X, Y, Z on the temperature T may generally be nonlinear. Therefore, in Figure 2a In the embodiment, at temperature T=T1, the light emitting device emits light, the color and brightness of which are determined by the temperature-dependent tristimulus values ​​X(T), Y(T), Z(T) and the operating current I and the peak operating current I max The linear factor is characterized by:

[0051]

[0052]

[0053]

[0054] The temperature-dependent tristimulus values X(T), Y(T), Z(T) describe the temperature dependence of the tristimulus values X, Y, Z, which temperature dependence is normalized to a linear dependence on the operating current I. It can also be said that the temperature-dependent tristimulus values X(T), Y(T), Z(T) are scaled by the relative current intensity I / I max to produce the tristimulus values X, Y, Z.

[0055] Figure 2b and Figure 2c shows the same light-emitting device at different temperatures T2 and T3, where T2 and T3 are different from and greater than T1, i.e., T1 < T2 < T3. In the exemplary embodiment shown here, the brightness increases, which is indicated by the increasing radial sunbeams, and the current supplied to the light-emitting device also increases, which is indicated by the increasing bars below the sunbeams. At Figure 2c the maximum values of the brightness, temperature, and current supplied to the light-emitting device are reached. As shown herein, in order to maintain or increase the brightness as the temperature increases, a higher electrical power is required. If the same electrical power is supplied at three different temperatures, the brightness will decrease because the brightness decreases as the temperature increases. To compensate for this, the electrical energy needs to be increased.

[0056] Figure 3 shows a schematic view of an array 300 of light-emitting devices 310. In the exemplary embodiment shown here, each light-emitting device 310 includes three light-emitting components 315a, 315b, 315c. Thus, the light-emitting component 315a mainly emits red light, which is indicated by "R"; the light-emitting component 315b mainly emits green light, which is indicated by "G"; and the light-emitting component 315c mainly emits blue light, which is indicated by "B". Thus, the light-emitting components can be light-emitting diodes, each of which emits light having a wavelength closely corresponding to its main emission color. For example, for red, the wavelength is 700 nm, for green, the wavelength is 546.1 nm, and for blue, the wavelength is 435.8 nm. Although specific wavelengths are specified herein, it should be conceived that this is done for exemplary purposes only and should not be considered restrictive. In the embodiment shown here, the color of the light emitted by each light-emitting device is the superposition of the light emitted from the corresponding light-emitting components 315a, 315b, 315c. Although the light-emitting device 310 in the embodiment shown here uses three light-emitting components 315a, 315b, 315c, it should also be conceived that each light-emitting device 310 can include more or fewer light-emitting components. It should also be conceived that each light-emitting device 310 can include only one light-emitting component. In this case, it can also be said that the light-emitting device 310 is a light-emitting component. In addition, it should be conceived that each light-emitting device 310 has a light-emitting component capable of emitting light of more than one specific wavelength.

[0057] In the embodiment shown here, the brightness of the corresponding light emitting assembly is also indicated by the length of the corresponding daylight beam. Thus, the length of the light beam indicates brightness. The light emitting device 310 in the middle of the array 300 has the highest brightness. In addition, in the middle of the array, each of the corresponding light emitting assembly 315a, 315b, 315c has the same brightness. Here, for example, white light is emitted because the superposition of red light, green light and blue light causes white light. However, it is conceivable that different colors can also be achieved by superimposing the light emitted from the corresponding light emitting assembly 315a, 315b, 315c. At the edge of the array 300, the light emitting assembly 315a, 315b, 315c has a larger blue part, which causes the wavelength of the emitted light to shift more to the blue spectrum. The configuration shown in the brightness of such arrays and light emitting assembly 315a, 315b, 315c can be used, for example, in the headlights of a car. For such applications, but also in other embodiments, it is important that the emission color of the array 300 does not change despite changes in the temperature of the light emitting devices 310 or even the light emitting components 315a, 315b, 315c. For this purpose, such temperature compensation as described herein is necessary and can be applied to each of the light emitting devices 310 of the array 300, or even to each of the light emitting components 315a, 315b, 315c of the array 300. It can therefore be said that the temperature of each of the light emitting devices 310 or even each of the light emitting components 315a, 315b, 315c is taken into account and the electrical energy supplied to the respective light emitting device 310 or light emitting component 315a, 315b, 315c is adjusted accordingly to achieve a respective target color point or to maintain a respective target color point. Obviously, a target color point can be defined individually for each light emitting device 310 or even each light emitting component 315a, 315b, 315c.

[0058] In order to maintain Figure 2a to Figure 2c In the example described in the context of , each of the light emitting components 315a, 315b, and 315c can be indexed in the above equation. Thus, the index i can be added to each tristimulus value x i , Y i , Z i and is added to the operating power, for example, to the operating current I i and the peak operating current I imax .

[0059] Therefore, it can be said that the peak operating current I imax and temperature T i The operating current I i The target tristimulus value X of the light beam obtained by operating the light emitting component t , Y t , Z t The contribution of is given by:

[0060]

[0061]

[0062]

[0063] Therefore, if the light from the three light emitting assemblies 315a, 315b, and 315c is to be mixed, the target tristimulus value X of the resulting light is t , Y t , Z t Will be given by:

[0064]

[0065]

[0066]

[0067] Thus, I1, I2 and I3 are the operating currents of the light-emitting components, I 1max ,I 2max and I 3max is the peak operating current of the light emitting component, and T1, T2 and T3 are the corresponding temperatures of the light emitting component. i (T), Y i (T) and Z i (T) are the temperature-dependent tristimulus values ​​of the three light-emitting components, indexed by i=1, 2, and 3.

[0068] The peak operating current of the light-emitting component (i.e. parameter l 1max , l 2max and l 3max ) may be fixed to avoid excessively high operating currents which may risk damaging the light emitting components due to, for example, overheating. i (T), Y i (T) and Z i The remaining temperature-dependent tristimulus values ​​of (T) are given and constitute the response functions of the light emitting components 315a, 315b and 315c to their respective temperatures. It can also be said that the three light emitting components X i (T), Y i (T) and Z i The temperature-dependent tristimulus values ​​of (T) are defined by the material parameters of the three light emitting components 315a, 315b, 315c. Therefore, if the target tristimulus values ​​X of the resulting light beam of the light emitting device 310 are given t , Y t , Z t, then the above equations must be solved for the operating currents l1, l2, and l3. Before solving the operating current, it is necessary to obtain the known peak operating current l of the light emitting device. 1max , l 2max and l 3max and temperatures T1, T2 and T3 to calculate the coefficients of the equation system.

[0069] Temperature-dependent tristimulus values ​​X of the three light-emitting components i (T), Y i (T) and Z i (T) constitutes the temperature-dependent three-stimulus matrix X(T) = [X i (T=T i );Y i (T=T i );Z i (T=T i )], the columns of the matrix are indexed by index i, and the matrix has a dependency on the temperature vector T = [T1, T2, T3]. Therefore, it can be said that the columns of the three stimulus matrices are each different temperatures T i For example, the i-th column of X(T) depends only on T i The rows of the tristimulus matrix X(T) correspond to different temperature-dependent color space dimensions X, Y, and Z. The temperature-dependent tristimulus matrix X(T) can be stored as a lookup table or using a set of approximation functions. However, the temperature-dependent tristimulus matrix X(T) can also be simplified by approximation.

[0070] A simplified approximation of the temperature-dependent three-stimulus matrix X(T) is that the matrix X(T) is only at the reference temperature T ref In other words, all temperatures of all light-emitting components are set to the reference temperature, T i =T ref In the example of three light emitting devices as described above, the reference temperature T ref The three stimulus matrix X ref , X ref =X(T = [T ref, T ref, T ref ]). In many cases, the temperature dependence of the temperature-dependent three-stimulus matrix X(T) can be modeled as a linear scaling relative to a reference temperature, where the linear scaling is the temperature T relative to the reference temperature T ref Therefore, in this linear scaling approximation, the temperature-dependent three-stimulus matrix X(T) is given by:

[0071]

[0072]

[0073]

[0074] therefore, is the light emitting component i at temperature T i The relative deviation of the temperature-dependent tristimulus values ​​X, Y, and Z under the reference temperature T. It can also be said that in the linear approximation, the temperature-dependent tristimulus matrix X(T) is composed of the reference temperature T ref The three stimulus matrix X ref and the matrix of relative deviations The binary product of is given by .

[0075] In a further simplifying approximation, one can assume that the relative deviation It is independent of the type of light-emitting component. In this case, it can be assumed that the relative deviation is a three-dimensional vector δ(T i )=[δ X (T i ), δ Y (T i ), δ Z (T i )]. It can also be said that in this approximation, the individual temperatures T of each light-emitting component i The relative deviation is entered, but the temperature dependence of the relative deviation itself is generic and independent of the specific type of lighting component. This has the advantage that only three temperature functions have to be stored in order to model the temperature dependence of the temperature-dependent tristimulus values ​​of all lighting components 315a, 315b and 315c.

[0076] In addition, the above approximation can be further simplified as:

[0077] X i (T i )=X i (T=T ref )+(T i，X )

[0078] Y i (T i )=Y i (T=T ref )+(T i，Y )

[0079] Z i (T i )=Z i (T=T ref )+(T i，Z )

[0080] Where T i,X Describes X iWith the change of temperature, T i，Y Describes Y i With the change of temperature, and T i，Z Describes Z i With the change of temperature.

[0081] Thus, if a target color point is given, for example, by specific tristimulus values, the aforementioned dependencies can be used to determine the electrical energy (e.g., current) that needs to be supplied to the respective light-emitting components 315a, 315b, and 315c, in accordance with the respective temperatures of the respective light-emitting components 315a, 315b, and 315c, in order to achieve the respective target color point. This allows a very fine temperature compensation, since it takes into account the contribution of each color individually. In the case where the light-emitting device 310 comprises three light-emitting components 315a, 315b, and 315c that primarily emit red, green, and blue light and refer to the RGB color space, it can also be said that each color is taken into account individually, since the respective temperatures of the respective light-emitting components 315a, 315b, and 315c are taken into account in the electrical energy determination.

[0082] Although in the embodiment example shown here, the light emitting device 310 has three light emitting components 315a, 315b and 315c, it is conceivable that each of the light emitting devices 310 includes more or fewer light emitting devices. Then, the above equations are changed accordingly. However, for the sake of simplicity, only the most common implementation with three light emitting components 315a, 315b and 315c is described, however, this should not mean that the present disclosure is limited to the corresponding most common case.

[0083] Figure 4 An exemplary block diagram of an electronic device 400 and a light emitting device 408 according to the present invention is shown. At least part of the electronic device 400 can be implemented in hardware and / or software, and can be implemented in a microcontroller and / or an integrated circuit. The light emitting device 408 can be an LED. The light emitting device 408 can include three light emitting components (not shown here), one of which can mainly emit light in the red spectrum, one light emitting component can mainly emit light in the green spectrum, and one light emitting component can mainly emit light in the blue spectrum. However, the light emitting device 408 should not be limited to this.

[0084] The electronic device 400 may include a receiving unit 402, which receives a target color point value, which is given by a tristimulus value in the embodiment example shown here. The value may be received from a controller (not shown here) different from the electronic device 400, or may have been preprogrammed into the electronic device 400. For example, a specific target color point may be associated with a specific function that at least one light-emitting device must implement. For example, if the light-emitting device is part of a taillight array of light-emitting devices, a target color point in the orange spectrum may be used as an indicator light, while a target color point in the red spectrum may be used as a brake light, and a target color point in the white spectrum may be used to indicate backward movement. In addition, it is also possible to adjust the intensity of the LED array according to the temperature, for example for a theater spotlight. However, these should only be used as examples and should not be considered to be limiting. In addition, in the embodiment example shown here, the receiving unit 402 also receives the temperature of the corresponding light-emitting device 408. The temperature may be measured by a sensor or derived from a sensing interval during an off interval of the light-emitting device 408. The receiving unit 402 transmits the target color point and the current temperature of the light-emitting device 408 to the determining unit 404.

[0085] The determination unit 404 may be a processor 404a or hardwired logic that takes the target color point and the temperature as inputs to determine an output, wherein the output is a target power that is required to operate the light emitting device 408 to achieve or maintain the target color point, depending on the current temperature of the light emitting device 408. Therefore, the determination unit 404 may have stored a lookup table in the memory 404b, in which corresponding approximate values ​​are stored to determine the power adjustment required for the light emitting device 408 to maintain or achieve the corresponding target color point. Therefore, the corresponding approximation is as shown in Figure 2a to Figure 2c and Figure 3 The approximation described in the context of . For example, the lookup table may include the standard deviation of the corresponding color component relative to a reference temperature. For example, at the reference temperature, no adjustment of the power is required. Here, the standard deviation may indicate that there is no deviation relative to the standard applied power. The deviation in temperature may indicate that a certain percentage of power needs to be increased or decreased in order to maintain or reach the corresponding target color point. This will allow the required power to be determined quickly or in almost real time, or respectively the deviation in the power demand.

[0086] Once the target electrical energy is determined, the information is passed from the determination unit 404 to the operation unit 406. The operation unit 406 can be a controller of a power source that provides electrical energy to the light-emitting device 408 or the power source itself. The target electrical energy passed from the determination unit 404 to the operation unit 406 can be an absolute value or a differential value. The absolute value can specify how much electrical energy needs to be provided to the light-emitting device 408. The differential value can specify the difference between the currently supplied electrical energy and the energy to be supplied. The operation unit 406 then provides the corresponding electrical energy to the light-emitting device 408 so that the light-emitting device 408 will still reach or maintain the corresponding target color point according to its current temperature. The electrical energy can be quantified as a voltage or current to be supplied to the light-emitting device 408.

[0087] Although only one light emitting device 408 is shown in the embodiment shown here, it is contemplated that multiple light emitting devices may also be provided by the same electronic device 400. Alternatively, each light emitting device 408 may also include its own electronic device 400. In addition, it is also contemplated that each light emitting device 408 includes at least one light emitting component. Therefore, the temperature information provided to the receiving unit 402 may include information of each of the light emitting devices 408 or each of the light emitting components, so that accurate temperature compensation of the light emitting component level is feasible.

[0088] Although specific hardware elements are described herein, this should not be construed as limiting and the invention should also encompass other hardware elements that can provide the same functionality as described herein.

Claims

1. A method for temperature compensation, the method comprising: receiving (102) a target color point of light emitted by at least one light emitting device (408); determining (104) operating power of the at least one light emitting device (408) based on a correlation of at least one temperature value of the at least one light emitting device with the received target color point; as well as The at least one light emitting device (408) is operated (106) based on the determined operating power.

2. The method according to claim 1, characterized in that The target color point comprises tristimulus values ​​of light emitted by the at least one light emitting device.

3. The method according to claim 1 or 2, characterized in that: The at least one temperature value occurs locally at the at least one light emitting device.

4. The method according to any one of the preceding claims, characterized in that The determining further comprises: A contribution of each of the at least one light emitting device to the received target color point is determined.

5. The method according to claim 4, characterized in that The contribution depends on the respective peak power to operate each of the respective light emitting devices.

6. The method according to claim 4 or 5, characterized in that: The contribution depends on the at least one temperature value of each of the respective light emitting devices.

7. The method according to any one of claims 4 to 6, further comprising: The contribution is stored in a lookup table as a function of a temperature value of each of the respective light emitting devices, wherein the lookup table is used to determine the operating power of each of the at least one light emitting device.

8. The method according to any one of claims 4 to 6, further comprising: The contribution of each of the respective light emitting devices at a standard temperature is stored in a vector, wherein the vector is used to determine the operating power of each of the at least one light emitting device.

9. The method according to claim 8, further comprising: The temperature dependence of the contribution is modeled by applying a corresponding relative deviation to the stored contribution at the standard temperature.

10. The method according to claim 9, characterized in that The standard temperature is 25°C.

11. The method according to claim 9 or 10, characterized in that: Each relative deviation depends on the at least one temperature value of each of the respective light emitting devices.

12. The method according to any one of the preceding claims, characterized in that The correlation consists of a system of linear equations.

13. The method according to any one of the preceding claims, characterized in that The received target color point comprises a brightness of light emitted by the at least one light emitting device.

14. The method according to any one of the preceding claims, characterized in that The at least one light emitting device includes at least one of a red light emitting diode (LED), a green light emitting diode (LED), and a blue light emitting diode (LED).

15. An apparatus (400) for temperature compensation of at least one light emitting device (408), the apparatus (400) comprising: A receiving unit (402) for receiving a target color point of light emitted by at least one light emitting device (408); a determination unit (404) for determining an operating power of the at least one light emitting device (408) based on a correlation between at least one temperature value of the at least one light emitting device (408) and the received target color point; as well as An operating unit (406) is used to operate the at least one light emitting device (408) based on the determined operating power.

Images