JP2007123153A - Illumination system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a simple illumination system with high accuracy for obtaining intended illumination light. <P>SOLUTION: The illumination system is composed of a light-emitting device capable of emitting three kinds of light separately, a control device controlling light emission of the light-emitting device, a light detection device capable of selectively detecting the light, and a feedback means generating feedback signals based on an output from the light detection device and supplying it to the control device. The feedback means generates d<SB>xy</SB>=(y<SB>0</SB>/x<SB>0</SB>)*X-Y, and d<SB>yz</SB>=Y-(y<SB>0</SB>/(1-x<SB>0</SB>-y<SB>0</SB>))*Z based on prescribed chromaticities x<SB>0</SB>, y<SB>0</SB>, from tristimulus values X, Y, Z based on the output of the light detection device to be supplied to the control device, and the control device controls light emission of the light emission device so that both differential mode signals d<SB>xy</SB>and d<SB>yz</SB>turn as near to zero as possible. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an illumination system including a light emitter using a plurality of LEDs having different emission wavelength characteristics, and in particular, a technique for adjusting the color and brightness of illumination light of an illumination system by controlling the forward current of the LED. About.

  2. Description of the Related Art Conventionally, a light emitter using red, green, and blue (RGB) LEDs (light emitting diodes) (hereinafter referred to as “LED base light emitter” in this specification) is an LCD (liquid crystal display device) as an illumination system. It has been widely used for backlight, indoor and outdoor lighting. However, the optical characteristics of LEDs fluctuate due to changes in temperature, forward current and aging in addition to differences depending on manufacturing lots, making it difficult to use LED-based light emitters extensively. Therefore, conventionally, a feedback system that controls the luminance and color of light emitted from a light emitter has been used in order to obtain illumination light of a predetermined quality.

In the RGB-based LED luminous body system described in Patent Document 1 as an illumination system, light from red, green, and blue (RGB) LED light sources each composed of a plurality of LEDs is mixed and output as white light as illumination light. is doing. A part of the illumination light is detected by a pre-filter photodiode and converted into an RGB signal. The RGB signal is linearly converted into a CIE 1931 standard tristimulus value X, Y, Z signal and then used as a reference tristimulus value signal (use The difference signal is obtained by comparison with the brightness and chromaticity input by the user. Subsequently, the difference signal is fed back to each LED light source, and the forward current of the LED of each LED light source is controlled so that the difference becomes zero. When such a system is adopted, measurement of individual LEDs and individual LED light sources is not required, and the demand for response characteristics of the LED drive circuit is eased.
JP 2004-52516 A

  In the illumination system described in Patent Document 1, some of the problems in the similar illumination system before that are solved. However, when the RGB signal is linearly converted to the tristimulus values X, Y, and Z signals. There is a problem that it is difficult to ensure the accuracy of the conversion even though the conversion accuracy and the comparison accuracy when obtaining the difference affect the performance of the illumination system.

  Accordingly, an object of the present invention is to solve or alleviate the above-described problems, and to provide a simple illumination system with high accuracy for obtaining desired illumination light.

An illumination system for solving the above-described problems includes a light-emitting device capable of individually emitting three types of light whose main light emission wavelength ranges are red (R), green (G), and blue (B), and the light-emitting device. A control device for controlling the emission of light, a light detection device capable of selectively detecting light in each of the light emission wavelength ranges, and a feedback for controlling light emission of the light emission device based on an output from the light detection device And a feedback means for generating a signal and providing it to the control device. The feedback means is a differential signal with a weight generated based on predetermined chromaticity x ₀ , y ₀ from tristimulus values X, Y, Z based on the output of the light detection device, that is, d _xy = ( y ₀ / x ₀ ) * X−Y and d _yz = Y− (y ₀ / (1−x ₀ −y ₀ )) * Z are generated and provided to the control device, The light emission of the light emitting device is controlled so that the difference signals d _xy and d _yz are both zero as much as possible.

The predetermined chromaticities x ₀ and y ₀ may be changeable according to an operator input.

  In the illumination system of the present invention, by generating a differential signal, the noise-to-noise characteristics with respect to common mode noise and the like are improved, and by adopting a null method, measurement sensitivity is improved and chromaticity can be adjusted with high accuracy. It is possible to provide a simple lighting system that is convenient to use and highly accurate. The details of other features and effects of the present invention will become clear from the following description.

  The embodiments of the present invention described below are for understanding the present invention and are not intended to limit the present invention to the embodiments. Therefore, the size and shape of the device and its elements are not intended to have a specific geometric relationship with the size or shape of the device or element that is actually manufactured. In addition, devices that exhibit similar functions and components thereof are given the same reference numerals as long as they do not completely coincide, but are considered to have no problem in understanding the present invention. In the following description of the embodiments, only the range necessary for understanding the invention is described for the wiring, electrical, and mechanical elements that connect the components. Further, the description of the parts belonging to the prior art is omitted or simplified.

  FIG. 1 is a schematic block diagram of an illumination system 100 according to an embodiment of the present invention. The illumination system 100 includes an LED light emitter unit 10, a light mixing unit 20, a color sensor unit 30, a tristimulus value conversion unit 40, a luminance / chromaticity value generation unit 50, a difference signal generation unit 60, and an LED drive control unit 70.

  The LED light emitter section 10 is a plurality of different types of LEDs (generally three types, which will be described in the following examples), which are mixed to give a desired color light. D3 and R (red) -LED driver 12, G (green) -LED driver 14, and B (blue) -LED driver 16 which are LED drivers respectively supplying driving (forward) currents to D3. Each of the LEDs D1, D2, and D3 may be composed of a single LED, or may be a composite LED in which a plurality of LEDs are combined in series, in parallel, or mixed and connected.

  The light mixing unit 20 is for obtaining the desired color light by mixing the light emitted from the LEDs D1, D2, and D3 of the LED light emitter unit 10, and spatially uniform the luminance and chromaticity of the color light. It is comprised with the member for making. Examples of members suitable for the light mixing unit 20 include various diffusers, reflectors, light tunnels, light pipes, wedge-shaped light guide plates, and tandem light guide plates.

  The color sensor unit 30 introduces a part of the color light from the light mixing unit 20 and performs spectroscopic analysis to give tristimulus values. A plurality of different types (in this description, three types: red (R), green) (G) and blue (B).) Sensor devices 32, 34, and 36 having spectral characteristics. Each of the sensor devices 32, 34, and 36 includes a photodiode R1, a G sensor, and a B sensor that detect the outputs of the photodiodes P1, P2, and P3 and output tristimulus values (RGB). The photodiodes P1, P2, and P3 may be configured by a single photodiode, or may be a composite photodiode in which a plurality of photodiodes are combined in series, in parallel, or in combination. When deriving chromaticity based on CIE1931 employed in the embodiment of the present application, it is preferable that the spectral characteristics of the color sensor unit 30 approximate the color matching function of CIE1931.

The tristimulus value conversion unit 40 is for inputting the output values (RGB) of each sensor device of the color sensor unit 30 and converting them into CIE tristimulus values X, Y, and Z. The output value of the color sensor unit 30 In another embodiment of the present invention in which the CIE tristimulus value is provided, the tristimulus value conversion unit 40 is unnecessary and is omitted or bypassed, and the output value of the color sensor unit 30 is directly compared with the difference signal generation unit 60. Is input. When it is difficult for the color sensor unit 30 to provide the CIE 1931 tristimulus values X, Y, and Z, the output values of the color sensor unit 30 (R, G, and B as shown in FIG. 1 in this description) are converted. [X Y Z] = [R G B] * [T] is obtained from a 3 × 3 matrix [T]. However, “*” is also used as a multiplication symbol when not confused in this specification. [T] = [T _ij ] is expressed by the i-th row and j-th column element T _ij of the matrix [T].

The light intensity S1, S2, S3 of the light emitted from the three kinds of LEDs D1, D2, D3, the output values R, G, B of the color sensor unit 30, and the tristimulus values X, Y, Z of CIE 1931 are respectively represented by vectors [D _LED ], [D _SENS ], [D _CIE ]. That is, [D _LED ] = [S1, S2, S3], [D _SENS ] = [R, G, B], [D _CIE ] = [X, Y, Z]. The spectral characteristics of the LEDs D1, D2, D3 and the sensor devices 32, 34, 36 are represented by matrices [B _LED ], [B _SENS ] having three column vectors, respectively, and the CIE 1931 color matching function (x ^(CIE) , y ^(CIE) , z ^(CIE) ) can also be expressed as a matrix [B _CIE ] consisting of three column vectors [x ^(CIE) ], [y ^(CIE) ], [z ^(CIE) ]. For example, the superscript “T” indicates transposition, and the superscript “−1” indicates an inverse matrix. (Normally, the color matching function of CIE 1931 is represented by x, y, and z with overline. In this specification, x ^(CIE) , y ^(CIE) , z having superscript ^(CIE) . ^(CIE) is used correspondingly.)
[D _SENS ] = [D _LED ] * ([B _LED ] ^T * [B _SENS ])
[D _CIE ] = [D _LED ] * ([B _LED ] ^T * [B _CIE ])
= [D _SENS ] * ([B _LED ] ^T * [B _SENS ]) ^-1 * ([B _LED ] ^T * [B _CIE ])
= [D _SENS ] * [T]
∴ [T] = ([B _LED ] ^T * [B _SENS ]) ^-1 * ([B _LED ] ^T * [B _CIE ])
FIG. 2 shows the conversion operation of the tristimulus value conversion unit 40 when the element is displayed as [T] = [T _ij ]. In FIG. 2, in one embodiment, R, G, and B inputs are received as analog signals, and analog calculations are performed to obtain stimulus values X, Y, and Z. The multiplication of the element T _ij can be realized by changing the amplification degree of the inverting and non-inverting amplifiers or simply setting the resistance value. The realization may be analog or digital. When the R, G, and B inputs are digitized, the conversion may be performed as one task of a digital signal processing device or a device including a microprocessor.

The luminance / chromaticity value generation unit 50 sends the luminance and chromaticity values (input values) set by the user by operating the keyboard, knobs, and buttons, and the luminance and chromaticity values transferred from inside and outside the lighting system to the CIE 1931. The compliant luminance L ₀ and chromaticity values x ₀ and y ₀ are transferred to the differential signal generation unit 60.

The difference signal generation unit 60 transfers the CIE 1931 tristimulus values X, Y, and Z input from the tristimulus value conversion unit 40 and the luminance / chromaticity value generation unit 50, as can be easily understood with reference to FIG. Then, a difference is obtained from the desired luminance L ₀ and chromaticity values x ₀ and y _0, and difference signals d _xy and d _yz are output to the LED drive control unit 70. First, the well-known relationship between the CIE 1931 stimulus values X, Y, Z and the luminance L, chromaticity values x, y is k = 683 (lm / W).
L = 683 * Y = k * Y
X = (x / y) * Y
Z = ((1-xy) / y) * Y
It is. Therefore, if the above equation is established by the desired chromaticity values x ₀ and y ₀ and the desired luminance L _o , the desired color light is supplied from the illumination system. Taking the difference as the extent that the above equation does not hold, the following three equations are obtained.

d _xy = (y ₀ / x ₀ ) * X−Y = α ₀ XY,
d _yz = Y− (y ₀ / (1−x ₀ −y ₀ )) * Z = Y−β ₀ Z, and
d _L = L−L _o = kY−L _o
Then, the LEDs D1, D2, and D3 are controlled so that stimulus values X, Y, and Z satisfying d _xy = d _yz = d _L = 0 are obtained, and colored light having a desired chromaticity is supplied from the illumination system. Like that. In FIG. 2, the multiplication of (y ₀ / x ₀ ) = α ₀ or (y ₀ / (1−x ₀ −y ₀ ) = β ₀ or k may be performed in the same manner as the multiplication of T _ij described above.

The LED drive control unit 70 extracts a matrix [A], which will be described later, representing the characteristics of the emitted light of each of the R, G, and B light emitting diodes D1, D2, and D3 from the [A] storage unit 72, and the difference from the [A] Based on the values of the differential signals d _xy , d _yz , and d _L from the signal generator 60, the light emission intensity of each LED is controlled. Light intensity control includes a method for increasing or decreasing the forward current of LEDs D1, D2, and D3 (AM method) and a method for controlling lighting time with a constant forward current (PWM method). it can.

  Next, the operation of the embodiment of the present invention will be described in more detail.

  Since any appropriate color matching function is a linear transformation of another appropriate color matching function, in the following, R, G, B light emitting diodes D1, D2, D3 within a range sufficient to understand the spirit of the present invention. It is assumed that each of the emitted lights is directly represented by CIE 1931-3 stimulation values X, Y, and Z, so that the explanation is easy to understand.

In the LED light emitter section 10, let R, G, B light emitting diodes D1, D2, D3 have spectral energy distributions E _R (λ), E _G (λ), and E _B (λ), respectively. Each outgoing light is received and detected by the photodiodes P1, P2, and P3 of the color sensor unit 30 via the light mixing unit 20, and is converted and output to CIE 1931-3 stimulation values as necessary by the tristimulus value conversion unit 40. The CIE 1931-3 stimulus value corresponding to the calibrated color matching function from the light mixing unit 20 to the input end of the tristimulus value conversion unit 40 is obtained at the output end. Here, in general, the 3 of the outgoing lights detected in the visible wavelength range according to the independent trichromatic functions [x ^(CIE) ], [y ^(CIE) ], [z ^(CIE) ]. the stimulus value, E for _{R (λ) (a Rx,} a Ry, a Rz), for _{E G (λ) (a Gx} , a Gy, a Gz), E for _{B (λ)} (a _Bx , A _By , A _Bz ).

By the way, in order to control the light emission intensity of each of the light emitting diodes D1, D2, and D3 in the LED light emitter unit 10 in accordance with a command from the LED control unit 70, the forward current is increased or decreased (corresponding to amplitude modulation) Since the ratio is increased or decreased (corresponding to pulse width modulation), the modulation coefficients P _R , P _G , P _B are applied to the emitted lights of the R, G, B light emitting diodes D1, D2, D3 with respect to a certain reference value (Hereinafter collectively (P _R , P _G , P _B ) and row vector display are also adopted), and the spectral energy distributions are P _R E _R (λ), P _G E _G (λ), P _B E _B (λ). Therefore, the spectral energy M (λ) of the mixed light is M (λ) = P _R E _R (λ) + P _G E _G (λ) + P _B E _B (λ), and 3 according to the three color matching functions. Stimulus values X, Y, and Z are displayed as row vectors, and [XYZ] = [P _R A _Rx + P _G A _Gx + P _B A _Bx P _R A _Ry + P _G A _Gy + P _B A _By P _R A _Rz + P _G A _Gz + P _B A _Bz ]. If displayed in matrix, it is as follows. Here, [W] = [X Y Z] ^T, (P) = In [P _R P _G P _B] ^T, [A] = [A _ij] = [[A _Rx A _Gx A _Bx] [A _Ry A _Gy A _By ] [A _Rz A _Gz A _Bz ]] ^T.

The difference signals d _xy , d _yz, and d _L are as described above (provided that “*” is a multiplication symbol (x), where x ₀ and y ₀ are predetermined chromaticity values to be realized and L ₀ is a predetermined luminance value). D _xy = α ₀ * X−Y, d _yz = Y−β ₀ * Z, d _L = L−L ₀ (where α ₀ = y) ₀ / x ₀ and β ₀ = y ₀ / (1−x ₀ −y ₀ )). Further, the luminance L of the illumination light, which is a mixed light of each outgoing light, takes a constant k = 683 (lm / W) and becomes L = kY. If these are displayed in matrix, they are as follows.

  If the above equation is modified, the following equation is obtained.

Here, as a condition for realizing the desired luminance value L ₀ and the chromaticity values x ₀ and y ₀ , if L−L ₀ = kY−L ₀ = d _L = d _xy = d _yz = 0, the feedback loop modulation coefficient vector convergence stabilization point (P) ^T = [P _R P _G P _B] converges to [P _0] ^T = [P _R0 P _G0 P _B0]. If the current modulation coefficient vector [P] ^T is different from [P ₀ ] ^T , the difference [ΔP] ^T = [P] ^T- [P ₀ ] ^T = [P _R −P _R0 P _G −P _G0 P _B −P _B0 ] is given by the following equation. The LED drive control unit 70 extracts the matrix [A] representing the characteristics of the emitted light of each of the R, G, and B light emitting diodes D1, D2, and D3 from the [A] storage unit 72 and calculates the difference [ΔP] ^T. Thus, the new modulation coefficient vector [P _N ] ^T = [P] ^T− [ΔP] ^T is updated. Thereafter, the sequential modulation coefficient vector is continuously updated by a controller or the like (not shown). It will be readily understood by those skilled in the art that [P _N ] ^T actually set may use [ΔP] ^T smoothed by time integration in order to further remove noise.

  Although the above assumes digital control that is generally calculated and controlled by a digital circuit including a microprocessor, those skilled in the art will understand that approximate control can be performed in an analog manner.

Further, in the control of the present invention, the spectral energy distributions E _R (λ), E _G (λ), E _B of the respective emitted lights of the R, G, B light emitting diodes D1, D2, D3 in the LED light emitter section 10 are used. Note that each change in (λ) is detected as a change in each of the elements P _R , P _G , P _B of the modulation coefficient vector [P] ^T. That is, even if the modulation coefficient vector [P] ^T is stable, it is necessary to adjust the modulation coefficient vector [P] ^T due to a change in temperature, physical disturbance, or the like. Therefore, if the detection of d _xy and d _yz is employed, there is a tendency to cancel the common mode noise superimposed on the input X, Y, and Z signals in the differential signal generation unit, and this has the advantage that the detection accuracy is improved. In particular, when the illumination light that is mixed light is white light, the chromaticity value is set to x ₀ = y ₀ = 1−x ₀ −y ₀ = 1/3, so that setting errors are included. However, the effect of canceling the influence of the noise in the detection of d _xy and d _yz is particularly high.

It is a schematic block diagram of the illumination system of one Example of this invention. It is a figure for demonstrating operation | movement of the tristimulus value conversion part of a lighting system, a brightness | luminance and chromaticity value generation part, and a difference signal generation part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 LED light-emitting part 20 Light mixing part 30 Color sensor part 40 3 Stimulus value conversion part 50 Luminance and chromaticity value generation part 60 Difference signal generation part 70 LED drive control part 100 Illumination system

Claims (7)

A light emitting device capable of individually emitting three types of light having main light emission wavelength ranges of red (R), green (G), and blue (B), a control device for controlling light emission of the light emitting device, and the light emission A photodetection device that can selectively detect light in each wavelength range, and a feedback that generates and provides a feedback signal for controlling the light emission of the light-emitting device based on the output from the photodetection device. A lighting system comprising:
The feedback means is a differential signal with a weight generated based on predetermined chromaticity x ₀ , y ₀ from tristimulus values X, Y, Z based on the output of the light detection device:
d _xy = (y ₀ / x ₀ ) * XY, and d _yz = Y- (y ₀ / (1−x ₀ −y ₀ )) * Z
Is generated and provided to the control device, and the control device is configured to control light emission of the light-emitting device so that the difference signals d _xy and d _yz are both as zero as possible. Lighting system characterized by The illumination system according to claim 1, wherein the predetermined chromaticities x ₀ and y ₀ can be changed according to an input by an operator. The illumination system according to claim 2, wherein the predetermined chromaticities x ₀ and y ₀ are stored in a memory IC in a rewritable or non-rewritable manner.   The feedback means receives the output from the light detection device and generates the tristimulus value, and the irradiation light emitting element receives the tristimulus value from the tristimulus value conversion means. 2. The illumination system according to claim 1, further comprising a difference signal generation unit configured to generate the difference signal, wherein the tristimulus value conversion unit and the difference signal generation unit are both disposed in proximity to the light detection device. .   The illumination system according to claim 4, wherein the tristimulus value conversion unit and the differential signal generation unit are mounted on a common substrate with the light detection device.   The illumination system according to claim 1, wherein the light emitting device includes a plurality of light emitting diode elements that emit light in different wavelength ranges.   The illumination system according to claim 1, wherein the light detection device includes an integrated color sensor.

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