METHOD FOR CONTROLLING A LIGHT EMITTING DIODE MIXER TO GENERATE WHITE LIGHT FROM A PROJECTOR, SYSTEM

Abstract

METHOD FOR CONTROLLING A LIGHT EMITTING DIODE MIXER TO GENERATE WHITE LIGHT FROM A PROJECTOR, SYSTEM Method for controlling light emitted by a projector comprising at least two groups of LEDs, each group comprising at least one LED, of which a first LED has a warm color temperature (CCTWW) and a second LED has a cool color temperature (CCTCW), said method comprising: Determination (DET1) of a plurality of corrected setpoint temperature (CCTCON_C(i)) from the control of a plurality of white light emissions from the projector at a predefined power of the LEDs; Calculation (K1) of coefficients called "warm white" (WWi) and "cool white" (CWi); Generation (GEN1) of a second model (M2) allowing the expression of a warm white coefficient (WWi) to be controlled as a function of the measured color temperature (CCTS); Control (PIL1) of the first group of LEDs and the second group of LEDs. Figure for the abbreviation: Fig. 1

Description

Title of the invention: METHOD FOR CONTROLLING A LIGHT-EMITTING DIODE MIXER TO GENERATE WHITE LIGHT FROM A PROJECTOR, SYSTEM Field of invention

[0001] The field of the invention relates to that of methods for controlling a projector, in particular projectors comprising different light-emitting diodes comprising different temperature colors in order to generate a given white light. More particularly, the field of the invention relates to methods for controlling an LED mixer in order to generate lighting in accordance with a color temperature setting. The field of the invention also relates to that of calibrating a projector so as to calibrate the white resulting from the mixing of the light produced by the LEDs of said projector. State of the art

[0002] Currently, we know LED lighting and projector lighting control solutions for professionals in audiovisual, cinema and photography.

[0003] The level of requirement for the precision of the color temperature and the light intensity produced by a projector requires control and mastery of the LEDs and the light mixer to produce lighting faithful to a given instruction.

[0004] The methods for controlling a projector comprising several groups of LEDs with different color temperatures require mastery of the equipment and the environment in order to obtain a good balance of the color temperatures of each LED to produce a desired color temperature.

[0005] However, light-emitting diodes can have margins of precision in their own color temperature which depend on the manufacturers. Furthermore, the photometric characteristics of LEDs change over time and the aging of the latter can affect the performance and stability of the light spectrum and therefore of their own color temperature.

[0006] Furthermore, manufacturers generally sort their components, particularly LEDs, at the end of production according to the characteristics of said components. One objective of this operation, called in English terminology "Binning", is to retain the LEDs offering the best characteristics, particularly with regard to the precision and stability of the color temperatures produced by the latter. A The problem is that this operation is costly, complex and requires LED quality management in relation to operating requirements. There is therefore a need to expand the use of all LEDs produced regardless of their performance by a process allowing calibration of a set of LEDs in a projector taking into account the intrinsic properties of the latter.

[0007] Another problem is that adjusting the LEDs is a complex operation that requires operations that are difficult to implement. This difficulty arises from the fact that each LED or group of LEDs has its own color temperature, so the set of LEDs must be calibrated so that the projector's light mixer produces white light that conforms to a desired light. It is most often necessary to model the dependence of the coefficients of each group of LEDs on a desired color temperature.

[0008] Currently, the methods for calibrating the LEDs of a projector are based on an upstream operation aimed at measuring the color temperatures of the LEDs produced and determining the coefficients of each group of LEDs from a linear formula. However, these coefficients are subsequently programmed on all the series projectors, regardless of the batch of LEDs. However, the sorting operations can lead to obtaining heterogeneous batches and lead to generating a color temperature of a mixer that is approximate with respect to a given setpoint.

[0009] These approximations result in offsets of several hundred Kelvin, which does not allow for obtaining precision in the desired white light color temperature under certain operating conditions. The problem of modeling the mixer coefficients combined with that of the stability of the color temperature emitted by an LED can lead to making non-compliant settings for a projector, i.e. which do not allow for obtaining a desired color temperature accurately.

[0010] An additional difficulty is that the light from LED projectors can change over time and automatic calibration is not always feasible to correct any possible equipment drift. This means that aging LEDs require replacement of the projectors when recalibration could correct the problem.

[0011] There is a need to provide a calibration method that is reliable and that allows a color temperature to be obtained with an accuracy of within 50 K of a desired color temperature.

[0012] More generally, there is a need to define a solution for calibrating LEDs of a projector in white light which is reliable and precise.

[0013] Finally, there is a need to exploit the lifespan of LEDs for a longer period despite their intrinsic drift. Summary of the invention

[0014] According to a first aspect, the invention relates to a method for controlling light emitted by a projector comprising at least two groups of LEDs, each group comprising at least one LED, of which a first LED has a warm color temperature, called "warm primary temperature" and a second LED has a cold color temperature, called "cold primary temperature", said method comprising: • Determination of a plurality of corrected temperature setpoints from the control of a plurality of white light emissions from the projector at a predefined power of two selected groups of LEDs, each lighting being controlled so that the measured color temperature corresponds substantially to a predefined color temperature setpoint defining a limit of a predefined interval and included in the range [2200 K; 6500 K]; • Recording of each corrected setpoint value for each defined interval; • Calculation of so-called “warm white” and “cold white” coefficients, said coefficients defining solutions of a first model, called “mixing model”, comprising a first function making it possible to obtain a corrected color temperature setpoint from a weighted mixture of each primary color temperature of each group of LEDs; • Generation of a second model, called a “control” model, making it possible to express a warm white coefficient to be controlled as a function, on the one hand, of the color temperature measured following the lighting of the projector and, on the other hand, of the light intensity, said warm white coefficient making it possible to control the first group of LEDs, said second model comprising a second exponential function defined in part on each predefined interval, the generation of the second model comprising the calculation of coefficients for each interval from the warm white coefficients and the cold white coefficients calculated by the first model and the color temperatures measured for each reference defining the limits of each predefined interval; • Acquisition of a desired color temperature and calculation of the warm white coefficient and the cold white coefficient from the second model, • Control of the first group of LEDs and the second group of LEDs of the projector with the warm white coefficient and the cold white coefficient calculated to produce a given lighting of the projector.

[0015] An advantage is to produce any white light with a desired color temperature from existing diodes whose performance is not known a priori.

[0016] According to one embodiment, the first model comprises for each interval a linear function in which the corrected setpoint temperature is a linear combination of the warm white coefficients and the cool white coefficients, the relationship being expressed as follows: CCTCon_c(î) = WWi» CCTWW + CW* CCTcw, where CCTWW is the primary color temperature of a first group of LEDs and CCTcw is the primary color temperature of a second group of LEDs.

[0017] An advantage is to define valid coefficients with a simple relationship at the limits of the intervals.

[0018] According to one embodiment, the second model is a model generated from the assumption of the following relationship for each interval boundary: WW = F2i(CCT) = A; • el Cl eCCTREF_M(i)j, oq a. and Ci are constants defined on each interval and CCTref mQ) is the measured color temperature. An advantage is that the coefficients are defined with an exponential function model which allows a better approximation of the actual color temperature curve.

[0019] According to one embodiment, the second model is a model applied to any desired color temperature setpoint included in a given interval and within which the following relationship is verified: WW = F2i(CCT) = Ai • el Cl *CCTS)J, where A; and Ci are constants defined on each interval and CCTS is the desired color temperature. An advantage is that an exponential function model allows a better approximation of the real color temperature curve, in particular between the reference points defining the limits of each interval.

[0020] According to one embodiment, when the projector comprises a plurality of groups of LEDs each having a different primary color temperature, the acquisition of a desired color temperature makes it possible to select a pair of groups of LEDs surrounding said desired value and the method comprising the control of said two groups of LEDs of the projector.

[0021] An advantage of such a projector is that it allows its operating range to be extended to produce a wide variety of white lights with a plurality of LED groups having color temperatures distributed across the entire color temperature range. Another advantage is that it allows narrower intervals to be defined and selected and thus a finer adjustment of a combination of two LED groups to be defined to produce white light having a color temperature within the interval defined by the two selected LED groups.

[0022] According to one embodiment, each primary temperature of each group of LEDs is obtained by measuring the temperature of the color temperature at 100% light intensity of said LED group and 0% of other LED groups. An advantage is to actually measure the color temperature of a light produced by a group of LEDs and to trust the measurement made rather than a temperature announced by a manufacturer.

[0023] According to one embodiment, each primary temperature of each group of LEDs is obtained by reading a value recorded in a memory.

[0024] According to one embodiment, the measurement of the color temperatures when controlling the projector is carried out by means of a spectrometer. One advantage is to obtain a high level of precision in the measurements of the color temperatures of the emitted lights. One advantage is to carry out a precise calibration of the projector.

[0025] According to one embodiment, the color temperature measurements resulting from the light emission produced by the projector are carried out with a spectrometer arranged as close as possible to the light emitter and in dark conditions.

[0026] According to one embodiment, five predefined intervals and 6 values ​​defining the limits of the intervals and therefore defining the color temperature setpoint values ​​for establishing the second model.

[0027] One advantage is to make the most of good coverage of the extent of the color temperature range while having interval limits that are not too far apart to produce mixtures that meet a sufficient level of requirement and precision. Defining too many intervals can lengthen the first calibration sequence before producing a new color mixture. A definition of 3 to 10 intervals is a good compromise.

[0028] According to one embodiment, the predefined power corresponds to 100% of the power of an LED.

[0029] According to one embodiment, a corrective factor is applied to each predefined color temperature setpoint and the desired color temperatures to take into account the color temperature shift of the measurements induced by the ambient temperature. An advantage is to take into account the environmental conditions in which the measurements are carried out.

[0030] According to a second aspect, the invention relates to a system for controlling white light emitted by a projector comprising at least two groups of LEDs, at least one LED of a first group comprising a warm color temperature, and at least one LED of a second group of LEDs comprising a cold color temperature, said system comprising a spectrometer for measuring the color temperatures and a calculator and a memory for carrying out the steps of the method of the invention. An advantage is to have equipment making it possible to produce mixtures of diode colors while calibrating the projector in a preliminary phase.

[0031] According to one embodiment, the system comprises a controllable mixer making it possible to configure the power of each group of LEDs from a received color temperature setpoint.

[0032] According to one embodiment, the system comprises a controllable mixer making it possible to address at least three groups of LEDs each having a primary color temperature, a calculator making it possible, upon receipt of a color temperature setpoint, to select two groups of LEDs according to the value of said setpoint. Brief description of the figures

[0033] Other characteristics and advantages of the invention will emerge on reading the detailed description which follows, with reference to the appended figures, which illustrate: • [Fig.l]: an embodiment of the main steps of the method of the invention; • [Fig.2]: an embodiment of a system of the invention; • [Fig.3]: an example of representation of a function expressing the coefficient warm color temperature based on the color temperature measured at different light intensities produced by the projector. • [Fig.4]: a representation of the warm white and cold white coefficients for different color temperatures. Definitions

[0034] • CCTWW primary warm color temperature of at least one LED measured for a predefined power. • CCTcw: primary cold color temperature of at least one LED measured for a predefined power. • CCTmw: primary color temperature between a cool color temperature and a warm color temperature of at least one LED measured for a predefined power. • CCTMWi, CCTmw2, CCTmw3: series of primary color temperatures between a cold color temperature CW and a warm color temperature WW of at least one LED calculated for a predefined power. • CCTtc(i): theoretical color temperature predefined or calculated when determining the coefficients of the CWw and CCw coefficients at 100% of the projector's luminous intensity. • CCTref mQ): measured color temperature of white light emitted by a projector for a theoretical color temperature value CCT te(i) and obtained from a corrected setpoint temperature CCTCon_c(î)- CCTCon_c or CCTcon_c(î) ■ corrected setpoint temperature allowing the projector to be controlled so that the measured color temperature CCTref M or CCTREF M(i) corresponds to the desired color temperature within a margin. WW; : warm color temperature coefficient for driving at least one LED emitting light having a warm color temperature, the index i referring to one of the limits of the color temperature interval INT; at which the measurement is considered. This coefficient can also be noted Cww to designate a warm white coefficient in a general manner without consideration of the measurement interval INT;. CW; : cold color temperature coefficient for driving at least one LED emitting a cold color temperature, the index i referring to one of the limits of the color temperature interval INT; at which the measurement is considered. This coefficient can also be noted CCw to designate a cold white coefficient in a general manner without consideration of the measurement interval INT;. CTTs: color temperature desired by a user of the light emitted by the white light projector. It corresponds to the theoretical color temperature CCTtc used during calibration at the REFi reference point. The color temperature CCTs corresponds to the actual result of the color mixing that can be compared to the measured color temperature value CCTREF M(i) or theoretical CCTts in order to evaluate the accuracy of the process. Fi: function defining the first model. F2i: function defining the second model M2 on an INT; color temperature interval. F2 defines the function over the set of INT; color temperature intervals. CW range: temperature range in cool white; WW range: temperature range in warm white; NW range: temperature range in neutral white. CCw, CW Coefficient: coefficient used to control the group of LEDs with a primary color temperature in the CW range. It corresponds to the percentage of luminous power of the LED. Cww, Coefficient WW: coefficient used to control the group of LEDs with a primary color temperature in the WW range. It corresponds to the percentage of luminous power of the LED. CNW, NW Coefficient: coefficient used to control the LED group having a primary color temperature in the NW range. It corresponds to the percentage of luminous power of the LED. System of the invention

[0035] The system of the invention comprises a projector comprising a plurality of white light LEDs. According to one embodiment, the projector comprises different groups of LEDs, the groups being formed according to the temperature colors of each LED. The color temperature of an LED is called its primary color or its primary color temperature. The projector of the invention comprises at least two groups of LEDs, each group comprising at least one LED and having a primary color temperature. [Fig. 2] represents a block denoted ML comprising all the groups of LEDs, here denoted LEDww and LEDcw for the group of LEDs having a warm color temperature and respectively for the group of LEDs having a cold color temperature.

[0036] The system of the invention comprises a CTR controller shown in [Fig.2] making it possible to control each group of LEDs, or even each LED independently. [Fig.2] represents a group of LEDs denoted LEDww representing a group of LEDs having a primary temperature in warm white and a group of LEDs denoted LEDcw having a primary color temperature in cold white. The power PK of the projector can for example be controlled from the CTR controller.

[0037] This control is carried out in particular using coefficients WWi, CW; which are calculated from a model. The control includes in particular the control of the power of each group of LEDs from the calculation of these coefficients. The controller may include a coordination component aimed at controlling each group of LEDs in a coordinated manner. This makes it possible, for example, to adjust the general brightness of the projector and to maintain it while modifying the white balance of the different groups of controlled LEDs.

[0038] The technique of producing a given white light from several LEDs of different primary temperature colors is more generally called a white color mixing technique. This technique is also called in English terminology "Tunable White Lighting", or also "tunable CCT" or "CCT tunable".

[0039] The system may comprise for this purpose an acquisition interface according to a DMX information exchange protocol in order to address the different LEDs or groups of LEDs of a projector with specific instructions. A DMXi interface is shown in [Fig.2]. The communication interface represents the physical interface for receiving or transmitting data from other equipment. This interface is capable of receiving and processing a color temperature value measured by a spectrometer, or a color temperature defined by a user interface (not shown) allowing the acquisition of an instruction from a user's setting. The latter is noted CCTs.

[0040] Other information exchange protocols are compatible with the invention, namely, control protocols such as SaCN, ArtNet, RDM, etc. More generally, the method and system of the invention can implement any wired or wireless information exchange protocol.

[0041] The system of the invention comprises a calculator K and a memory making it possible to carry out calculations, in particular to produce the mathematical model(s) defining functions for controlling and driving the groups of LEDs from a color temperature setpoint to be produced. The calculator can also be configured to use the model in order to calculate the warm white WW; and cold white CW; coefficients used to drive the groups of LEDs.

[0042] Finally, the method of the invention comprises a spectrometer (not shown in [Fig.2]) for reliably and accurately measuring the color temperatures produced by the projector. The spectrometer makes it possible in particular to produce a measured value of the color temperature. The latter can be used to control the setpoint temperature actually applied when a difference between the initial setpoint temperature and the measurement is too large.

[0043] According to another embodiment, the color temperature measurements can be carried out by any other photometric measurement system comprising a suitable sensor. LED groups

[0044] Generally, for controlling a projector comprising several groups of LEDs, a color temperature setpoint that is desired to be obtained from the projector will be provided. A control module for each group of LEDs is then responsible for recovering the desired setpoint temperature CCTS and for defining, according to a control law, what proportion of lighting of each group of LEDs it is necessary to determine to obtain this color temperature of the projector. The control module for each group of LEDs controls each group of LEDs in a coordinated manner with its own setpoint expressed in the form of white coefficients so that the light produced and measured corresponds to the desired setpoint color temperature CCTS.

[0045] The LEDs are grouped so that their own color temperature, also called "primary color temperature", is substantially the same. It is recalled that a primary color temperature of an LED is the temperature obtained by switching on said LED, measured in a preferably black or dark environment. The measurement is preferably carried out for a given intensity level, for example at 100% of the intensity of the LED. Thus, a color temperature of a LED can be between 2200K and 6500K.

[0046] Indeed, light-emitting diodes are available in a range of color temperatures which is measured in kelvins (K) and is generally referred to as color temperature. The color temperature of an LED determines the hue of the light emitted by the LED.

[0047] In the present description, an LED emitting light of a color temperature is categorized according to the primary color temperature range it emits. • A first range called warm white, also called in Anglo-Saxon terminology “Warm White” and noted WW, when the color temperature is between 2200K and 3500K. This color temperature produces a yellow light similar to that of a classic incandescent bulb. • A second range called neutral white, also called in Anglo-Saxon terminology “Neutral White” and noted NW, when the color temperature is between 3500K and 4500K. This color temperature offers a slightly brighter and less yellow white light than warm white. • A third range called cool white, also called in Anglo-Saxon terminology "Cool White" and noted CW, when the color temperature is between 4500K and 6500K - This color temperature produces a clean white light with a slightly bluish tint. This third range is also called Daylight Range, also called in Anglo-Saxon terminology "Daylight". This range can extend beyond 6500 K which is a color temperature close to natural daylight.

[0048] This categorization allows for a better understanding, the whole invention only requires the definition of two groups of LEDs having two color temperatures in the wide range [2200 K, 6500 K]. A projector having a plurality of groups of LEDs distributed in the range will allow a better calibration and a better selection of two groups of LEDs most suitable for producing a given light.

[0049] A group of LEDs can comprise at least one LED, however when the LEDs are grouped together within a projector, the power level of the latter is generally linked to the number of LEDs it comprises, to their arrangement, to the maximum power of each LED and the primary color temperature of each LED. In order to simplify the control of a projector, the latter groups together different groups of LEDs, each group of which can be controlled in power. An interest is to obtain any color temperature in the range from coordinated control of each group of LEDs to obtain a given light output and a desired color temperature. Primary color temperature

[0050] Thus, a first group of LEDs having a primary temperature in a WW range, for example 3200 K and a second group of LEDs having a primary temperature in a CW range, for example 5800 K, will make it possible to obtain any temperature color in the range [3200 K; 5800 K] by carrying out a controlled mixture of the powers of each of the two groups of LEDs.

[0051] To measure the primary color temperature of a group of LEDs, the latter is turned on at 100% of its power by turning off the other groups of LEDs of the projector. In this case, only the color temperature of a specific group of LEDs is measured. One advantage is to refer precisely to the primary color temperature of a group of LEDs. This makes it possible to avoid considering a primary color temperature that has potentially drifted or is affected by a drift of an LED of the group. This action can be repeated on each group of LEDs.

[0052] According to one embodiment, the primary color temperatures CCTWW, CCTMW, CCTcw of each group of LEDs are known and already measured. The primary color temperatures can therefore in this case already be recorded in a memory in order to use them during subsequent calculations of warm white and cool white coefficients. In this case, the method of the invention does not include the step of measuring the primary temperature colors of the groups of LEDs.

[0053] According to another embodiment, the primary color temperatures CCTWW, CCTmw, CCTcw of each group of LEDs can be calculated at each new launch or calibration of the projector.

[0054] The measurements can be initiated for example at each new production of light produced by the projector from which a desired color temperature CCTs is desired.

[0055] According to another embodiment, these measurements can be decorrelated from a new adjustment of the projector to produce a given light and are in this case carried out at frequencies specific to the calibration of the projector. Case of more than three LED groups

[0056] The invention relates to any projector comprising at least two groups of LEDs each having a primary color temperature. The invention also applies to any projector comprising a plurality of groups of LEDs having different color temperatures in a given range. In order to obtain a desired color temperature, the two groups of LEDs surrounding the temperature setpoint of desired color CCTS will be preferentially chosen. However, another combination is possible by considering at least two groups of LEDs whose color temperature frames the desired color temperature CCTS setpoint.

[0057] To this end, coefficients, noted Cww and CCw, are defined to control the light power of each group of LEDs.

[0058] The coefficient Cww makes it possible to set the quantity of light power of a group of LEDs having a primary color temperature in the WW range and the coefficient Ccw makes it possible to set the quantity of light power of a group of LEDs having a primary color temperature in the CW range in order to control the mixer. The invention also applies to coefficients CNW for controlling groups of LEDs in the NW range. However, in the remainder of the description, the notations CCw and Cww will be used with regard to a non-limiting example of two groups of LEDs having respectively a color temperature in the cold white CW and one in the warm white WW.

[0059] If we consider a mixer of two groups of LEDs each having a primary color temperature, the following relationship is verified: Ccw = IL - CWw, where IL is a percentage of luminous intensity, or a percentage of the luminous power. The IL value is between 0 and 1. When the measurements and / or calculations are carried out for a maximum intensity of the projector, i.e. 100%, IL = 1.

[0060] It is recalled that this relationship remains true in the case where a first group of LEDs in the NW range and a second group of LEDs in the WW range are selected with the relationship CNW = IL - Cww. Identically, this relationship also remains true in the case where a first group of LEDs in the NW range and a second group of LEDs in the CCW range are selected with the relationship CNW = IL-Ccw.

[0061] In some configurations, a projector has several groups of LEDs, each having a primary color temperature. In this case, it is possible to segment the color temperature range to establish an automatic selection of the LED groups according to the color temperature setpoint received.

[0062] The method of the invention is therefore applicable to cases of 3, 4, or even 5 or 6 groups of LEDs. For example, for a range of 2200K to 6500K, if one wishes to increase the precision of the control of the temperature color produced by the projector, it may be chosen to increase the number of groups of LEDs and to choose them so that their primary color temperature is distributed over the range of values.

[0063] According to one example, four groups of LEDs whose primary CCTs are 2200K, 4000K, 5500K and 6500K can be chosen. For each defined CCT range, a group of LEDs will be operated that is most suitable for obtaining a desired color temperature value CCTs that is as precise as possible. The method of the invention allows to obtain a CRI value close to the maximum value of the CRI of the LEDs whatever the value of the desired CCTs setpoint, in particular whether it is in a low range or a high range of the range [2200 K, 6500 K]. Beach segmentation

[0064] From two selected groups of LEDs, the method of the invention makes it possible to determine the control instructions specific to these two groups of LEDs. For this, the method of the invention implements a solution combining a non-linear model defined by part and a segmentation of the value range from reference values ​​defining the limits of sub-intervals of the range is used.

[0065] The segmentation of the value range makes it possible to define portions of curves expressing the warm white coefficient WW as a function of the value of the desired temperature setpoint CCTs. The segmented intervals of the value range [2200K to 6500K] are called INT;. Second M2 model

[0066] The method of the invention makes it possible to rely on a second model called model M2 making it possible to obtain a warm white coefficient WW as a function of a set temperature of a desired color temperature CCTs. An equivalent relationship can be defined linking the cold white coefficient CW with the desired color temperature setpoint.

[0067] The model M2 can be written as a function defined by parts whose validity is delimited by the limits of an interval INTi.

[0068] Cww(i) = F2i(CCTs) = IL • A; • ciCl •«'^i

[0069] The function F2i is chosen according to the interval INT; in which the desired color temperature CCTs lies. The function F2i is defined by function coefficients A; and Ci defining the function on each interval.

[0070] An advantage of the exponential function is that it allows a better approximation of the real curve expressing the white coefficients with the desired temperature color.

[0071] It can be noted that the model M2 of the invention is a continuous model, thus the functions {F2i}ieLi ;NJ are continuous when passing from an interval INT; to another interval INTi i or INTi+i. This condition allows us to define the coefficients of each function F2i from reference points defining the limits of each interval INT;.

[0072] We consider the following reference points: REF;, defining a lower bound of an interval INT;.

[0073] The theoretical temperature setpoint CCTts(i) is the desired temperature setpoint CCTs corresponding to the reference point REFJ when the ca is carried out liberation of the CCw and Cww coefficients of the LEDs. The notion of corrected setpoint temperature CCTCon_c(î) is introduced in the present invention to obtain a measured color temperature, noted CCTREF M(i), which is substantially equal to the theoretical setpoint temperature.

[0074] In order to determine the coefficients Ai, Ci of the functions F2i on each interval, we apply the functions with values ​​to each interval boundary INT;.

[0075] The M2 model can be written as follows:

[0076] Cww(i) = F2i(CCT) = IL • A; • ci Cl .cctref.moj

[0077] Where: • A; and Ci are coefficients to be determined to produce a valid model in a range INT; of color temperature. The model is valid for two groups of LEDs making it possible to frame a color temperature setpoint that one wishes to achieve by a mixture of said two selected groups. • CCTref mQ) corresponds to the color temperature measured in the INT range;.

[0078] [Fig.4] represents the two curves fixing the values ​​of the white coefficients warm white Cww and cool white CCw allowing each group of LEDs to be driven, each having a color temperature, to obtain a desired color temperature at the output of the mixer and the projector. [Fig.4] represents the two curves of the actual color temperature values ​​relating to each group of LEDs WW and CW represented by plots 10 and 12 to produce a given color temperature. Curves 11 and 13 represent linear approximations of a model which can sometimes lead to generating significant deviations when driving the groups of LEDs. The invention makes it possible to obtain better control fidelity for a projector thanks to a model allowing better modeling of the calculation of these coefficients.

[0079] In order to calculate the coefficients Ai and Ci, the method of the invention makes it possible to define a segmentation of the range of color temperature values ​​into several ranges or intervals from the definition of color temperature reference values, denoted REF;. The reference values ​​REF; can be chosen arbitrarily or can be chosen according to the primary color temperatures of each group of LEDs of the projector. It may be interesting to choose limits not corresponding to the primary color temperatures in order to calibrate the mixtures for each range INT;. Reference values ​​will preferably be chosen which make it possible to cover the largest range of values ​​with sufficient spacing between the reference values ​​REF;. One interest is to find a compromise between, on the one hand, a high number of intervals in order to approach the theoretical curve and on the other hand a low number of intervals in order to reduce calculations and the calibration phase.

[0080] According to one example, 5 intervals are defined. The invention covers all embodiments that may include 1 interval, 2 intervals up to 15, or even 20 intervals. Some embodiments may implement more intervals than 20 in order to obtain increased precision.

[0081] In the remainder of the description, an exemplary embodiment will be considered in which the range of values ​​[3100 K, 5700 K] is divided into 5 INT intervals; also noted INT;, thus noted: • INÏ! = [REFb REF2] = [3100 K, 4000 K] • INT2 = [REF2, REF3] = [4000 K, 4500 K] • INT3 = [REF3, REF4] = [4500 K, 5000 K] • INT4 = [REF4, REF5] = [5000 K, 5500 K] • INT5 = [REF5, REF6] = [5500 K, 5700 K]

[0082] With 6 reference points R EF defining the limits of said intervals INT;: • REF! = 3100K • REF2 = 4000 K • REF3 = 4500 K • REF4 = 5000 K • REF5 = 5500 K • REF6 = 5700 K

[0083] More generally, we note an interval INT; = [REF;, REFi+i].

[0084] The method of the invention makes it possible to calculate all the coefficients A;, Q on each interval INT;.

[0085] For each of these reference values ​​REF;, corrected color temperature setpoint values, denoted CCTCon_c-, are calculated iteratively. Indeed, when a theoretical temperature setpoint CCTtc is received, without correction, the measured color temperature CCTREF M may be different by several hundred Kelvins, in particular for the reasons set out in the prior art.

[0086] We note the color temperatures CCTtc(i), CCTCon_c(î), CCTREF M(i) which will be received, respectively calculated and respectively measured relative to each interval INT;.

[0087] The method of the invention therefore comprises a first step, represented by step DETi of [Fig.l], aimed at determining a plurality of corrected setpoints CCTCon_c from the control of a plurality of white light emissions from the projector at a predefined power Pk of two groups of selected LEDs.

[0088] The method of the invention advantageously makes it possible to choose the limits of each interval REF; initially as the desired color temperature setpoint REF; = CCTtc(i) at a time t0 corresponding to the start of the calibration.

[0089] The LEDs selected for the projector are preferably those which have a primary color temperature surrounding the theoretical color temperature setpoint CCTte(i).

[0090] Each lighting of the projector is controlled by the two groups of LEDs selected so that the measured color temperature CCTREF_M(i) corresponds substantially to a theoretical color temperature CCTtc(i) considered as a reference when determining the coefficients Cww and CCw defining a REFi terminal of a predefined interval INT; included in the range [3100 K; 5700 K].

[0091] The control consists of varying the powers of the two groups of LEDs in a coordinated manner so that the temperature at the output of the mixer and the projector which is measured CCTREF M(i) converges towards the theoretical color temperature CCTtc(i) which corresponds to a terminal REF;. When this temperature is reached to within a margin, for example to within 50K, a memory records the corrected setpoint temperature CCTCoN_c(i) making it possible to obtain the desired color temperature at the output of the projector, i.e. the values ​​of the reference points defining the limits of each interval INT;.

[0092] We then obtain for each REF; terminal of each INT; interval: • A corrected setpoint temperature: CCTCon_c(1) to obtain a measured color temperature CCTREF M(1) = REFi; • A corrected setpoint temperature: CCTCon_c(2) to obtain a measured color temperature CCTREF M(2) = REF2; • A corrected setpoint temperature: CCTCon_c(3) to obtain a measured color temperature CCTREF M(3) = REF3; • A corrected setpoint temperature: CCTCon_c(4) to obtain a measured color temperature CCTREF M (4) = REF4; • A corrected setpoint temperature: CCTCon_c(5) to obtain a measured color temperature CCTREF M (5) = REF5.

[0093] The method makes it possible to iterate the measurements until, within a margin, equality between the measured temperature and the value of the reference point is obtained. These iterations can be carried out automatically using an algorithm controlling the value of the corrected setpoint until substantially equality is obtained.

[0094] [Fig.l] represents the second recording step ENRi of the method of the invention consisting of recording the corrected color temperature setpoint values ​​CCTCoN_c(i) for each reference point REF.

[0095] When the corrected setpoint temperatures are calculated and recorded CCT coN_c(i), the method of the invention makes it possible to calculate so-called “hot white” coefficients WW; and so-called “cold white” coefficients CW; of a mixture model Mb also called first model Mb

[0096] [Fig.l] illustrates this third step noted Ki of calculations of the warm white and cold white coefficients at the reference points from a first model Mb

[0097] The coefficients define solutions of the first model Mi called the “mixture model”. This mixture model Mi corresponds to a first function Fi making it possible to express a corrected color temperature setpoint CCTCon_c(î) to obtain a measured color temperature CCTREF M(i) at a reference point REFi from a weighted mixture of each light produced by two groups of LEDs having a primary color temperature CCTWW, respectively CCTCw- The power of each group of LEDs is defined to obtain the color temperature at the output of the mixture which corresponds to a limit of an interval.

[0098] The function Fi(CCTww, CCTcw) can be expressed as follows:

[0099] CCTcoN.c(i) = WWi» CCTWW + CW^ CCTcw.

[0100] Where WW; is a warm white coefficient for configuring the power of a first group of LEDs and where CW; is a cool white coefficient for configuring the power of a second group of LEDs.

[0101] And where CCTWW is the primary temperature color of a first group of LEDs and CCTcw is the primary temperature color of a second group of LEDs.

[0102] The method of the invention takes into consideration a hypothesis which considers that such a CCT value corresponding to the corrected setpoint is the sum of the primary CCTs of the two groups of LEDs multiplied by the coefficients of warm white WW! and cold white CW; to be determined. These coefficients represent a weighting of each power of the group of LEDs which is controlled.

[0103] The two coefficients make it possible to obtain a predefined luminous intensity of the projector, for example 100% with respect to the possible power of the projector. The invention takes advantage of carrying out the measurements at 100% of the power of the projector. The first model Mi is therefore generated from an assumption of a luminous intensity at 100% of the power of the projector. However, other embodiments are possible by taking into consideration a predefined intermediate power of the projector which is kept constant for each setpoint temperature and each defined interval.

[0104] These measurements make it possible to construct a second model M2, detailed below, which will be kept for calibrations at intermediate powers.

[0105] The method makes it possible to obtain a second, more precise M2 model over the entire light intensity range.

[0106] The following relationship is therefore verified: WW; + CW; = 1 or 100%.

[0107] This relationship remains true for each reference point REF; of the range that was previously segmented. It is therefore possible to deduce the coefficients WW; and CW; for each terminal of each interval INT;.

[0108] We obtain the following expression:

[0109] WW; = (CCTcon.cG) - CCTcw) / (CCTWW - CCTcw)

[0110] The method allows, thanks to the iterations of the color temperature measurements making it possible to obtain, within a margin, equality between the measured temperature and the value of the reference point, to fix the value of the coefficients WW; and CW;. The value of the coefficients is obtained with a desired precision thanks to the adjustment of the value of the color temperature setpoint defining the corrected setpoint.

[0111] These iterations can be carried out automatically from an algorithm controlling the value of the corrected setpoint until a given precision of the value of the coefficients is obtained.

[0112] The method of the invention therefore makes it possible to obtain for each reference point REF i corresponding to each interval terminal INT;, the following values ​​of the warm white coefficients WW; and cold white coefficients CW;:

[0113] WW! = (CCTcon_c(1) - CCTcw) / (CCTWW - CCTcw)

[0114] WW2 = (CCTcon_c(2) - CCTcw) / (CCTWW - CCTcw)

[0115] WW3 = (CCTcon_c(3) - CCTcw) / (CCTWW - CCTcw)

[0116] WW4 = (CCTcon_c(4) - CCTcw) / (CCTWW - CCTcw)

[0117] WW5 = (CCTcon_c(5) - CCTcw) / (CCTWW - CCTcw)

[0118] And

[0119] CW^l-WW!

[0120] CW2 = 1 - WW2

[0121] CW3 = 1 - WW3

[0122] CW4 = 1 - WW4

[0123] CW5 = 1 - WW5

[0124] For each defined interval INT;, we have therefore, according to the values ​​of the terminals REF; of these latter intervals, calibrated the projector to calculate a corrected setpoint temperature CCTCon_c(î) allowing to obtain the desired value at the projector output of color temperature. This corrected setpoint temperature CCTCon_c (i) allowed us to calculate the coefficients of warm white WW; and cold white CW; from a relation defining the mixture of lights produced by two groups of LEDs. This results in a deduction of the coefficients of each group of LEDs corresponding to the corrected setpoint temperature values ​​actually applied to the projector to produce the desired color temperature. These coefficients are only true at the limits of the defined intervals.

[0125] The method of the invention makes it possible to generate a second model M2 defined by part on each interval and to apply it between two limits of an interval INT;, where the following relation is assumed to be modeled:

[0126] WWi = F2i (CCT) = A; • ci Cl .CCTJ,

[0127] Here the color temperature CCT defines the variable of the function. It corresponds either to the desired color temperature CCTs when the model M2 is generated, or to the measured color temperature CCTREF M(i) for each REF; interval terminal in order to define the coefficients A,, Q of the model.

[0128] The function F2i is defined by part on each interval INT;. We thus have a continuous function defined by the set of functions F2b F22, F23, F24, F25.

[0129] We always have CW; = IL - WWi, where IL is the luminous intensity of the projector. This relationship can also be expressed as a percentage by adapting coefficients restoring a proportion.

[0130] We then have CW; = 100% - WW;

[0131] [Fig.l] represents a step noted GENi aiming to generate the second model M2 by calculating the coefficients of a function defined by part on each interval INT;

[0132] We thus have the following set of relations which are verified on each interval:

[0133] WWi = F21(CCT) = Ai • c1 Cl .cctref_m(dj

[0134] WW2 = F22(CCT) = A2 • C1 C2 .CCTREF_M(2)J

[0135] WW3 = F23(CCT) = A3 • C1 c î .CCTREF_M(3)J

[0136] WW4 = F24(CCT) = A4 • cl C4 .CCTREF_M(4)J

[0137] WW5 = F25(CCT) = A5 • cl C5 .CCTREF_M(5)J

[0138] The coefficients A, and C; are therefore calculated by continuity of the curve over the entire color temperature range for the previously calculated WW; and CW; values.

[0139] We obtain the following relationship:

[0140] Q = (In (WWi+1 / WW;)) / (WWi+1 - WW;),

[0141] where In is the natural logarithm

[0142] A; = WWi+1 / eiCi .ccTcoN_c(i+i)j

[0143] We can thus calculate for each interval the coefficients C; and A;:

[0144] Ci = (In (WW2 / WWi)) / (WW2 - WWi)

[0145] C2 = (In (WW3 / WW2)) / (WW3 - WW2)

[0146] C3 = (In (WW4 / WW3)) / (WW4 - WW3)

[0147] C4 = (In (WW5 / WW4)) / (WW5 - WW4)

[0148] C5 = (In (WW6 / WW5)) / (WW6 - WW5)

[0149] and

[0150] Ai = WW2 / ClCI •CCTREF_M(2)J

[0151] A2 = WW3 / elC2 •CCTREF_M(3)J

[0152] A3 = WW4 / elC3 •CCTREF_M(4)J

[0153] A4 = WW5 / elC4 •CCTREF_M(5)J

[0154] A5 = WW6 / elC5 •CCTCON_C(6)J

[0155] Thus on each interval INT;, the method of the invention makes it possible to obtain the function F2i of the model thanks to the calculation of each coefficient Q and A;.

[0156] Consequently, the method of the invention makes it possible to obtain the coefficients of warm white WW; and cold white CW; to control each group of LEDs.

[0157] The method of the invention makes it possible to acquire a desired color temperature setpoint CCTs in the range of values ​​[3100 K, 5700 K]. According to another embodiment, this operating range can be extended.

[0158] This step of acquiring a color temperature to be produced by the projector is noted ACQi in [Fig.l].

[0159] Depending on the acquired color temperature value, a range is selected in which this temperature lies. For example, if the desired color temperature value CCTs is in the interval INT3 = [REF3, REF4] = [4500 K, 5000 K], then the portion of curve F23 valid over this interval INT3 of the model M2 is applied.

[0160] The function F23(CCTs) makes it possible to deduce the warm white coefficient WW3 to control the group of LEDs having a primary temperature in warm white.

[0161] The method of the invention also makes it possible to deduce the cold white coefficient CW3 to be applied to the group of LEDs having a color temperature in cold white.

[0162] The projector is then controlled so as to produce a mixture of light power making it possible to obtain the desired CCTs temperature color. This control step is noted PILi in [Fig.l].

[0163] [Fig.3] represents test measurements making it possible to represent measurements of color temperatures produced by a projector controlled using the method of the invention with different brightness levels.

[0164] One advantage of this representation is that it allows these values ​​to be compared with the actual values ​​measured using a spectrometer. It is therefore possible to quantify the difference between the model produced using the method of the invention and the actual measurements.

[0165] The function F2i previously described is defined piecewise for a brightness of 100% as calculated in the previous steps. The corresponding curves are also represented for brightnesses at 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20% and 10%.

[0166] These curves are obtained by generating warm white and cold white coefficients whose value is a proportion of the desired power.

[0167] An advantage of the method and system of the invention is to allow automatic self-calibration of the projector before generating white light having a desired color temperature CCTs. For this purpose, the reference values ​​REFi can be predefined. According to another embodiment, these values ​​can be defined via a system user interface. Self-calibration can be controlled on demand. In other words, each time the projector is used, calibration may or may not be a prerequisite for generating a new color temperature. For example, this calibration may be initiated every N uses of the projector or be performed when the projector is switched on or be performed at a given time frequency.

[0168] The solution of the invention offers a possibility of mixing these different LEDs or groups of LEDs in order to obtain a desired CCTs color temperature at + / - 50K over a range of 2200 to 6500K. In addition, the method of the invention makes it possible to maintain the desired CCTs color temperature value regardless of the requested light power level from 0 to 100% of the range while maintaining the illumination value.

[0169] Furthermore, the method of the invention makes it possible to maintain a color rendering index CRI greater than or equal to 92. By multiplying the LEDs, this figure can make it possible to obtain a CRI greater than 95 over a wider CCT range.

[0170] Finally, the method of the invention offers the possibility of rapid and precise automatic calibration of the luminaires over the entire range of desired color temperatures CCTs ranging from 2200 K to 6500 K and for different types of given LEDs.

[0171] A direct effect of the invention is to allow the LEDs to be kept for longer. Indeed, the method of the invention allows automatic calibration of a projector equipped with LEDs having an intrinsic drift by adapting the light setpoint by calculating coefficients adapted for each group of LEDs.

Claims

Claims

1. Method for controlling a light emitted by a projector comprising at least two groups of LEDs, each group comprising at least one LED, of which a first LED has a warm color temperature (CCTWW), called "warm primary temperature" and a second LED has a cold color temperature (CCTCw), called "cold primary temperature", said method comprising: • Determination (DETi) of a plurality of corrected temperature setpoints (CCTCoN_c(i)) from the control of a plurality of white light emissions from the projector at a predefined power (Pk) of two selected groups of LEDs, each lighting being controlled so that the measured color temperature (CCTREF M(i)) corresponds substantially to a predefined color temperature setpoint (REFi, CCTtc(i)) defining a limit of a predefined interval (INT;) and included in the range [2200 K; 6500 K]; • Recording (ENRi) of each corrected setpoint value (CCTcon_c(î)) for each interval (INT;) defined; • Calculation (KJ of coefficients called “warm white” (WW;) and “cold white” (CW;), said coefficients defining solutions of a first model (MO, called “mixing model”, comprising a first function (FO making it possible to obtain a corrected color temperature setpoint (CCTCon_c(î)) from a weighted mixture of each primary color temperature (CCTWW, CCTCw) of each group of LEDs; • Generation (GENO) of a second model (M2), called “control” model, making it possible to express a warm white coefficient (WW;) to be controlled as a function of, on the one hand, the measured color temperature (CCTREF M(i)) following the lighting of the projector and, on the other hand, the light intensity, said warm white coefficient (WW0) making it possible to control the first group of LEDs, said second model (M2) comprising a second exponential function (F2i) defined in part on each predefined interval (INT;), the generation of the second model (M2) comprising the calculation of coefficients (Ai, Ci) for each interval (INT;) from the coefficients of warm whites (WWi) and cold white coefficients (CWi) calculated by the first model (Mi) and measured color temperatures (CCTREF M(i)) for each reference (REF(i)) defining the limits of each predefined interval (INT; ); • Acquisition (ACQi) of a desired color temperature (CCTs) and calculation of the warm white coefficient (WW) and the cold white coefficient (CW) from the second model (M2), • Control (PILi) of the first group of LEDs and the second group of LEDs of the projector with the warm white coefficient (WW) and the cold white coefficient (CW) calculated to produce a given lighting of the projector.

2. Method according to any one of the preceding claims, characterized in that the first model (MJ) comprises for each interval (INTi) a linear function in which the corrected setpoint temperature (CCTCon_c(î)) is a linear combination of the warm white coefficients (WW;) and the cold white coefficients (CW;), the relationship being expressed as follows: CCTcoN.c(i) = WW;. CCTWW + CWi • CCTcw, where CCTWW is the primary color temperature of a first group of LEDs and CCTcw is the primary color temperature of a second group of LEDs.

3. Method according to any one of the preceding claims characterized in that the second model (M2) is a model generated from the hypothesis of the following relation for each interval boundary (INTi): WW = F2i(CCT) = Ai • el-Ci.CCTREF_M(i)J5 where A; and Ci are constants defined on each interval (INT;) and CCTREF M(i) is the measured color temperature.

4. Method according to any one of the preceding claims, characterized in that the second model (M2) is a model applied to any desired color temperature setpoint (CCTs) included in a given interval (INT;) and within which the following relationship is verified: WW = F2i(CCT) = A; • ei-Ci .CCTSA where A; and Ci are constants defined on each interval (INT;) and CCTS is the desired color temperature.

5. Method according to any one of the preceding claims, characterized in that when the projector comprises a plurality of groups of LEDs each having a different primary color temperature (CCTWW, CCTMWi, CCTcw), the acquisition of a desired color temperature (CCTs) makes it possible to select a pair of groups of LEDs surrounding said desired value (CCTs) and the method comprising the control of said two groups of LEDs of the projector.

6. Method according to any one of the preceding claims characterized in that each primary temperature (CCTWW, CCTMW, CCT cw) of each group of LEDs is obtained by a measurement of the temperature of the color temperature at 100% luminous intensity of said group of LEDs and at 0% of the other groups of LEDs.

7. Method according to any one of claims 1 to 5 characterized in that each primary temperature of each group of LEDs is obtained by reading a value recorded in a memory.

8. Method according to any one of the preceding claims, characterized in that the measurement of the color temperatures (CCTREF M(i)) during the control of the projector is carried out by means of a spectrometer.

9. Method according to any one of the preceding claims, characterized in that the color temperature measurements resulting from the light emission produced by the projector are carried out with a spectrometer arranged as close as possible to the light emitter and in dark conditions.

10. Method according to any one of the preceding claims characterized in that 5 predefined intervals (INT;) and 6 values ​​defining the limits (REF;) of the intervals (INT;) and therefore defining the color temperature setpoint values ​​for establishing the second model (M2).

11. Method according to any one of the preceding claims, characterized in that the predefined power (Pk) corresponds to 100% of the power of an LED.

12. Method according to any one of the preceding claims, characterized in that a corrective factor is applied to each predefined color temperature setpoint (CCTtc(i)) and desired color temperatures (CCTs) to take into account the color temperature shift of the measurements induced by the ambient temperature.

13. System for controlling a white light emitted by a projector comprising at least two groups of LEDs, at least one LED of a first group comprising a warm color temperature (CCTWW), and at least one LED of a second group of LEDs comprises a cold color temperature (CCTcw), said system comprising a spectrometer for measuring the color temperatures and a calculator and a memory for carrying out the steps of the method of any one of the preceding claims.

14. System according to claim 13 characterized in that it comprises a controllable mixer making it possible to configure the power of each group of LEDs from a received color temperature setpoint.

15. System according to claim 13 characterized in that it comprises a controllable mixer making it possible to address at least three groups of LEDs each having a primary color temperature, a calculator making it possible, upon receipt of a color temperature instruction, to select two groups of LEDs according to the value of said instruction.

Images