Calibration system for a spectral luminometer and a method for calibrating a spectral luminometer Number:7,151,600 from the United States Patent and Trademark Office (PTO) owispatent A calibration light source outputs emission lines having a known emission-line wavelength, a spectral luminometer to be calibrated measures an emission-line output of the calibration light source, and a system control unit calibrates the wavelength of the spectral luminometer by estimating the wavelength of the emission-line output from ratios of outputs of a light receiving unit at a plurality of measurement wavelengths neighboring an emission-line wavelength and estimating a wavelength change amount from a difference between the estimated wavelength of the emission-line output and the known emission-line wavelength. The wavelength and the sensitivity of a spectral luminometer can be calibrated at a user side.<H luminometer, calibrating, Calibration, sys, 7151600.html, Patent, pto, 7151600

Title: Calibration system for a spectral luminometer and a method for calibrating a spectral luminometer

Abstract: A calibration light source outputs emission lines having a known emission-line wavelength, a spectral luminometer to be calibrated measures an emission-line output of the calibration light source, and a system control unit calibrates the wavelength of the spectral luminometer by estimating the wavelength of the emission-line output from ratios of outputs of a light receiving unit at a plurality of measurement wavelengths neighboring an emission-line wavelength and estimating a wavelength change amount from a difference between the estimated wavelength of the emission-line output and the known emission-line wavelength. The wavelength and the sensitivity of a spectral luminometer can be calibrated at a user side.

Patent Number: 7,151,600 Issued on 12/19/2006 to Imura

Inventors: Imura; Kenji (Toyohashi, JP)
Assignee: Konica Minolta Sensing, Inc. (Osaka, JP)

Appl. No.: 10/733,370

Filed: December 12, 2003

Foreign Application Priority Data


Jul 25, 2003 [JP]			2003-201726

Current U.S. Class: 356/326 ; 356/300; 356/328

Current International Class: G01J 3/00 (20060101); G01J 3/18 (20060101)

Field of Search: 356/300,326,328

Foreign Patent Documents


63-006426	Jan., 1988	JP
04-106430	Apr., 1992	JP
06-058817	Mar., 1994	JP
6-74823	Mar., 1994	JP
2002-116087	Apr., 2002	JP
2003-060291	Feb., 2003	JP
2003-090761	Mar., 2003	JP
2003-188468	Jul., 2003	JP

Primary Examiner: Evans; F. L.
Attorney, Agent or Firm: McDermott Will & Emery LLP

Claims

What is claimed is:

1. A calibration system comprising: a calibration light source which outputs emission lines having a known emission-line wavelength; a spectral luminometer which is to be calibrated, and provided with a light receiver having an array of photoelectric conversion elements for receiving lights produced by dispersing an incident light in accordance with wavelengths and outputting electrical signals corresponding to light intensities of the respective received wavelength components, and adapted to measure an emission-line output of the calibration light source; a wavelength estimator which estimates a wavelength of the emission-line output from relative outputs of the light receiver at a plurality of measurement wavelengths neighboring the emission-line wavelength when the spectral luminometer measures the emission-line output of the calibration light source; and a wavelength calibrator which calibrates the wavelength of the spectral luminometer by estimating a wavelength change amount from a difference between the estimated wavelength of the emission-line output and the known emission-line wavelength.

2. A calibration system according to claim 1, wherein: the spectral luminometer further includes a memory which stores in advance a correspondence table of output ratios of the light receiver at the plurality of measurement wavelengths neighboring the emission-line wavelength and the wavelength of the emission-line output; and the wavelength estimator estimates the wavelength of the emission-line output from the output ratios measured by the spectral luminometer and the correspondence table.

3. A calibration system according to claim 1, wherein the calibration light source includes: a semiconductor laser which emits a laser beam; a plurality of monitor sensors having different spectral sensitivities near an output wavelength of the semiconductor laser; and an output wavelength estimator which estimates the output wavelength of the semiconductor laser from output ratios of the plurality of monitor sensors.

4. A calibration system according to claim 3, wherein: the calibration light source further includes a memory which stores in advance a correspondence table of the output ratios of the plurality of monitor sensors and the output wavelength of the semiconductor laser; and the output wavelength estimator estimates the output wavelength of the semiconductor laser from the output ratios of the plurality of monitor sensors and the correspondence table.

5. A calibration system according to claim 4, wherein: the calibration light source further includes a temperature sensor which detects temperatures of the plurality of monitor sensors; the memory stores a plurality of correspondence tables corresponding to a plurality of temperatures of the plurality of monitor sensors; and the output wavelength estimator estimates the output wavelength of the semiconductor laser based on the output ratios of the plurality of the monitor sensors and the temperature detected by the temperature sensor.

6. A calibration system according to claim 1, wherein the calibration light source further includes: an incandescent light source; a plurality of monitor sensors having different spectral sensitivities; and a spectral intensity distribution estimator which estimates a spectral intensity distribution of the incandescent light source from outputs of the plurality of the monitor sensors.

7. A calibration system according to claim 6, further comprising: a light receiver output estimator which estimates an output of the light receiver from the spectral intensity distribution estimated by the spectral intensity distribution estimator and the spectral sensitivities of the respective photoelectric conversion elements of the light receiver when the spectral luminometer measures the emission-line output of the calibration light source; a calculator which calculates a ratio of the estimated output of the light receiver to an actual output of the light receiver for each photoelectric conversion element; and a sensitivity calibrator which calibrates the sensitivity of the spectral luminometer based on the calculated ratio for each photoelectric conversion element.

8. A calibration system according to claim 6, wherein: the calibration light source further includes a memory which stores in advance a correspondence table of the output ratios of the plurality of monitor sensors and a relative spectral intensity distribution of the incandescent light source; and the spectral intensity distribution estimator estimates the relative spectral intensity distribution of the incandescent light source from the output ratios of the plurality of monitor sensors and the correspondence table.

9. A calibration system according to claim 8, wherein: the calibration light source further includes a temperature sensor which detects temperatures of the plurality of monitor sensors; the memory stores a plurality of correspondence tables corresponding to a plurality of temperatures of the plurality of monitor sensors; and the spectral intensity distribution estimator estimates the relative spectral intensity distribution of the incandescent light source based on the output ratios of the plurality of the monitor sensors and the temperature detected by the temperature sensor.

10. A calibration system according to claim 1, further comprising: a calculator which calculates a ratio of an emission-line intensity obtained from the outputs of the light receiver at a plurality of measurement wavelengths neighboring the emission-line wavelength to an output of the light receiver at a wavelength having no sensitivity at the emission-line wavelength; a comparator which compares the calculated ratio with an initial value of the ratio stored beforehand; and a stray-light level estimator which estimates a change in a stray-light level of the spectral luminometer based on result of the comparator.

11. A calibration system according to claim 1, further comprising: a calculator which calculates a half-width of the light receiver near the emission-line wavelength based on the outputs of the light receiver at a plurality of measurement wavelengths neighboring the emission-line wavelength; a comparator which compares the calculated half-width with an initial value of the half-width stored beforehand; and a half-width estimator which estimates a change in a half-width of the spectral luminometer based on result of the comparator.

12. A calibration system according to claim 1, wherein the spectral luminometer further includes: a tristimulus value calculator which calculates tristimulus values based on the outputs of the light receiver at the respective measurement wavelengths and weight coefficients for the respective wavelengths, the tristimulus value calculator correcting the weight coefficients according to the wavelength change amount and calculating the tristimulus values using the corrected weight coefficients.

13. A calibration system according to claim 12, wherein: the spectral luminometer further includes a memory which stores weight coefficients for wavelength errors; and the tristimulus value calculator calculates the tristimulus values by selecting a weight coefficient corresponding to the wavelength change amount from the weight coefficients stored in the memory.

14. A calibration system according to claim 1, wherein the calibration light source includes: a three-wavelength type fluorescent lamp; and a band pass filter having a center wavelength near the emission-line wavelength of the fluorescent lamp.

15. A calibration system according to claim 14, wherein the band pass filter is operable to adjust the incident angle of a beam propagating from the fluorescent lamp.

16. A calibration system according to claim 14, wherein the calibration light source is incorporated in the spectral luminometer.

17. A calibration system according to claim 1, wherein the calibration light source includes a low-pressure mercury lamp.

18. A calibration system according to claim 1, wherein the calibration light source includes a spectrocolorimeter.

19. A calibration system for calibrating a spectral luminometer including a light receiver having an array of photoelectric conversion elements for receiving lights produced by dispersing an incident light in accordance with wavelengths and outputting electrical signals corresponding to light intensities of the respective received wavelength components, comprising: a calibration light source which outputs emission lines having a known emission-line wavelength; a wavelength estimator which estimates a wavelength of the emission-line output from relative outputs of the light receiver at a plurality of measurement wavelengths neighboring the emission-line wavelength when the spectral luminometer measures the emission-line output of the calibration light source; and a wavelength calibrator which calibrates the wavelength of the spectral luminometer by estimating a wavelength change amount from a difference between the estimated wavelength of the emission-line output and the known emission-line wavelength.

20. A calibration system comprising: a calibration light source including an incandescent light source; a plurality of monitor sensors having different spectral sensitivities; a spectral intensity distribution estimator which estimates a spectral intensity distribution of the incandescent light source from outputs of the plurality of monitor sensors; a spectral luminometer which is to be calibrated, and provided with a light receiver having an array of photoelectric conversion elements for receiving lights produced by dispersing an incident light in accordance with wavelengths and outputting electrical signals corresponding to light intensities of the respective received wavelength components, and adapted to measure an output light of the incandescent light source; a light receiver output estimator which estimates an output of the light receiver from the spectral intensity distribution estimated by the spectral intensity distribution estimator and the spectral sensitivities of the respective photoelectric conversion elements of the light receiver when the spectral luminometer measures the output light of the incandescent light source; a calculator which calculates a ratio of the estimated output of the light receiver to an actual output of the light receiver for each photoelectric conversion element; and a sensitivity calibrator which calibrates the sensitivity of the spectral luminometer based on the calculated ratio for each photoelectric conversion element.

21. A calibration system for calibrating a spectral luminometer including a light receiver having an array of photoelectric conversion elements for receiving lights-produced by dispersing an incident light in accordance with wavelengths and outputting electrical signals corresponding to light intensities of the respective received wavelength components, comprising: a calibration light source including an incandescent light source; a plurality of monitor sensors having different spectral sensitivities; a spectral intensity distribution estimator which estimates a spectral intensity distribution of the incandescent light source from outputs of the plurality of monitor sensors; a light receiver output estimator which estimates an output of the light receiver from the spectral intensity distribution estimated by the spectral intensity distribution estimator and the spectral sensitivities of the respective photoelectric conversion elements of the light receiver when the spectral luminometer measures the output light of the incandescent light source; a calculator which calculates a ratio of the estimated output of the light receiver to an actual output of the light receiver for each photoelectric conversion element; and a sensitivity calibrator which calibrates the sensitivity of the spectral luminometer based on the calculated ratio for each photoelectric conversion element.

22. A method for calibrating a spectral luminometer, comprising the steps of: outputting emission lines having a known emission-line wavelength from a calibration light source; measuring an emission-line output of the calibration light source by a spectral luminometer which is to be calibrated, and provided with a light receiver having an array of photoelectric conversion elements for receiving lights produced by dispersing an incident light in accordance with wavelengths and outputting electrical signals corresponding to light intensities of the respective received wavelength components; estimating a wavelength of the emission-line output from relative outputs of the light receiver at a plurality of measurement wavelengths neighboring the emission-line wavelength; and calibrating the wavelength of the spectral luminometer by estimating a wavelength change amount from a difference between the estimated wavelength of the emission-line output and the known emission-line wavelength.

23. A method for calibrating a spectral luminometer, comprising the steps of: estimating a spectral intensity distribution of an incandescent light source from outputs of a plurality of monitor sensors; measuring an output light of the incandescent light source by a spectral luminometer which is to be calibrated, and provided with a light receiver having an array of photoelectric conversion elements for receiving lights produced by dispersing an incident light in accordance with wavelengths and outputting electrical signals corresponding to light intensities of the respective received wavelength components; estimating an output of the light receiver from the estimated spectral intensity distribution and the spectral sensitivities of the respective photoelectric conversion elements of the light receiver; calculating a ratio of the estimated output of the light receiver to an actual output of the light receiver for each photoelectric conversion element; and calibrating the sensitivity of the spectral luminometer based on the calculated ratio for each photoelectric conversion element.

Description

This application is based on patent application No. 2003-201726 filed in Japan, the contents of which are hereby incorporated by references.

BACKGROUND OF THE INVENTION

This invention relates to a calibration system for a spectral luminometer for measuring and evaluating luminances and colors of various light sources and display devices and particularly to a calibration system for a spectral luminometer for a wavelength calibration and a spectral sensitivity calibration, and a method for calibrating a spectral luminometer.

Spectral luminometers for measuring and evaluating spectral luminances, luminances and colors of various light sources and display devices have been conventionally widely used (for example, see Japanese Unexamined Patent Publication No. H6-74823). FIG. 18 is a diagram showing a construction of a light splitting unit in a prior art spectral luminometer. As shown in FIG. 18, a light splitting unit 310 built in the prior art spectral luminometer is the so-called polychrometer in which an incident beam through an incident slit 311 is dispersed by a diffraction grating 313, and a dispersed image of the incident slit 311 is formed on a light receiving sensor array 314 by a imaging optical system 312. This polychrometer simultaneously measures an intensity distribution of all the wavelengths in a measurement range. FIG. 19 is a graph showing spectral sensitivities of light receiving sensors S.sub.n (n=0 to 60) of the light receiving sensor array 314 of the polychrometer. The polychrometer shown in FIG. 19 has a half-width of 10 nm, and an interval between the sensors is 5 nm, and a wavelength range is from 400 to 700 nm. In FIG. 19, horizontal axis represents wavelength and vertical axis represents relative sensitivity. FIG. 19 shows only the relative sensitivities of the light receiving sensors S.sub.0, S.sub.1, S.sub.2, S.sub.30, S.sub.58, S.sub.59, S.sub.60.

As shown in FIG. 19, middle wavelengths of the lights received by the light receiving sensors S.sub.n do not always coincide with wavelengths obtained by dividing the wavelength range 400 to 700 nm by 60. Accordingly, a wavelength calibration for the light splitting unit 310 is carried out by using a monochromatic light source whose wavelength is known and stable and giving the spectral sensitivities of the respective light receiving sensors of the light receiving sensor array 314.

Further, a sensitivity calibration for the light splitting unit 310 is carried out by measuring an output light of a standard light source whose spectral intensity distribution is known and stable and storing sensitivity correction coefficients for the respective light receiving sensors in a controller 401 beforehand, the sensitivity correction coefficients being calculated as ratios of outputs of the respective light receiving sensors of the light receiving sensor array 314 to outputs the respective light receiving sensors should make based on the spectral sensitivities calculated by the wavelength calibration.

As shown in FIG. 18, a relative position change of optical elements of the polychrometer directly and sharply leads to a wavelength error. Further, a sensitivity error is caused by a property change of an optical element such as a reflection efficiency of the diffraction grating 313 and a circuit construction. This is also caused by the aforementioned wavelength error. Accordingly, occurrences of the wavelength error and the sensitivity error resulting from an over-the-time change or a thermal change are unavoidable and a recalibration is essential to maintain precision.

However, the recalibration to maintain the precision of the spectral luminometer requires the same facility and operation as the calibration at the time of production and, therefore, has been difficult to be done at a user side. Thus, a user needed to send the spectral luminometer back to a factory in order to have the spectral luminometer recalibrated. Such a recalibration made by sending the spectral luminometer back takes cost and time both at the producer side and at the user side and is difficult to do with a sufficient frequency. Further, in the case that a spare spectral luminometer is necessary as a substitution while the spectral luminometer is at the factory for the recalibration, and a cost therefor is also necessary.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a spectral luminometer calibration system and calibration method which are free from the problems residing in the prior art.

It is another object of the present invention to provide a spectral luminometer calibration system and calibration method which enable a user to calibrate the wavelength and sensitivity of the spectral luminometer.

A spectral luminometer is provided with a light receiver having photoelectric conversion elements for receiving lights produced by dispersing an incident light in accordance with wavelengths and outputting electrical signals corresponding to light intensities of the respective received wavelength components.

According to an aspect of the present invention, the wavelength of the spectral luminometer is calibrated by: outputting emission lines having a known emission-line wavelength from a calibration light source; measuring an emission-line output of the calibration light source by the spectral luminometer; estimating a wavelength of the emission-line output from relative outputs of the light receiver at a plurality of measurement wavelengths neighboring the emission-line wavelength; and estimating a wavelength change amount from a difference between the estimated wavelength of the emission-line output and the known emission-line wavelength.

According to another aspect of the present invention, the sensitivity of the spectral luminometer is calibrated by: estimating a spectral intensity distribution of an incandescent light source from outputs of a plurality of monitor sensors; measuring an output light of the incandescent light source by the spectral luminometer; estimating an output of the light receiver from the estimated spectral intensity distribution and the spectral sensitivities of the respective photoelectric conversion elements of the light receiver; calculating a ratio of the estimated output of the light receiver to an actual output of the light receiver for each photoelectric conversion element to calibrate the sensitivity of the spectral luminometer.

These and other objects, features and advantages of the present invention will become more apparent upon a reading of the following detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a construction of a calibration system for a spectral luminometer according to an embodiment of the invention;

FIG. 2 is a graph showing a relative spectral intensity of a calibration light source and a spectral transmittance of a filter in a monitor sensor;

FIG. 3 is a diagram showing a collimating optical system and the monitor sensors of the calibration light source when viewed from a diffusing plate;

FIG. 4 is a graph showing an emission-line wavelength of an emission-line light source and relative spectral sensitivities of five light receiving sensors near the emission-line wavelength;

FIG. 5 is a diagram showing the calibrating system for the spectral luminometer upon setting a first correspondence table of the calibration light source;

FIG. 6 is a diagram showing the calibrating system for the spectral luminometer upon setting a second correspondence table of the calibration light source;

FIG. 7 is a diagram showing the calibrating system for the spectral luminometer upon setting a third correspondence table of the calibration light source;

FIG. 8 is a graph showing how to estimate a half-width of the spectral luminometer to be calibrated;

FIG. 9 is a flowchart showing an operation of the calibrating system for the spectral luminometer;

FIG. 10 is a flowchart showing a subroutine "Output Wavelength Calculation" executed in Step S7 of FIG. 9;

FIG. 11 is a flowchart showing a subroutine "Spectral Sensitivity Calculation" executed in Step S8 of FIG. 9;

FIG. 12 is a diagram showing a construction of a calibration system according to another embodiment, showing a portion thereof near an emission-line light source and an incandescent light source;

FIG. 13 is a graph showing a spectrum when a three-wavelength type fluorescent lamp is used as an emission-line light source;

FIG. 14 is a diagram showing how to adjust a transmission wavelength of a band pass filter;

FIG. 15 us a graph showing emission-line spectra of a low-pressure mercury lamp;

FIG. 16 is a diagram showing the spectral luminometer having the emission-line light source incorporated thereinto in the second embodiment;

FIG. 17 is a diagram showing the spectrocolorimeter having the emission-line light source incorporated thereinto in the second embodiment;

FIG. 18 is a diagram showing a construction of a light splitting unit in a prior art spectral luminometer; and

FIG. 19 is a graph showing spectral sensitivities of light receiving sensors of a light receiving sensor array of a polychrometer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE PRESENT INVENTION

Embodiments of the present invention are described with reference to the accompanying drawings. It should be noted that no description is given on the same construction by identifying it by the same reference numerals in the respective drawings.

Referring to FIG. 1 showing a construction of a calibration system for a spectral luminometer according to an embodiment of the invention, a calibration system 1 for a spectral luminometer is provided with a calibration light source 100, a spectral luminometer 200 to be calibrated and a system control unit 300 connected with the light source calibration 100 and the spectral luminometer 200.

The calibration light source 100 includes a controller 101, an emission-line light source 102, an incandescent light source 103, a diffusing plate 104, a collimating optical system 105, a first monitor sensor 106 (106a, 106b), a second monitor sensor 107 (107a, 107b), a third monitor sensor 108 (108a, 108b), a temperature sensor 109 and a storage 120.

The storage 120 is formed, for example, by an EEPROM (Electrically Erasable Programmable Read-Only Memory) and functions as a first correspondence-table storage 120a and a second correspondence-table storage 120b.

The first correspondence-table storage 120a stores a first correspondence table showing a correspondence of an output wavelength .lamda..sub.m and an output ratio I.sub.10/I.sub.20, which is a ratio of an output I.sub.10 of the first monitor sensor 106 to an output I.sub.20 of the second monitor sensor 107, for each temperature. The first correspondence table is described later.

The second correspondence-table storage 120b stores a second correspondence table showing an correspondence of a relative spectral intensity distribution R(.lamda.), an output ratio I.sub.30/I.sub.10, which is a ratio of an output I.sub.30 of the third monitor sensor 108 to the output I.sub.10 of the first monitor sensor 106, and an output ratio I.sub.20/I.sub.10, which is a ratio of the output I.sub.20 of the second monitor sensor 107 to the output I.sub.10 of the first monitor sensor 106, for each temperature. The second correspondence table is described later.

The controller 101 is formed, for example, by a CPU (Central Processing Unit) and functions as an output wavelength estimator 101a and a spectral intensity distribution estimator 101b.

The output wavelength estimator 101a estimates the output wavelength .lamda..sub.m of the emission-line light source 102 from an output ratio I.sub.1/I.sub.2, which is a ratio of an output I.sub.1 of the first monitor sensor 106 to an output I.sub.2 of the second monitor sensor 107, with reference to the first correspondence table stored in the first correspondence-table storage 120a.

The spectral intensity distribution estimator 101b selects a relative spectral intensity distribution R(.lamda.) of the incandescent light source 103 based on an output ratio I.sub.3/I.sub.1, which is a ratio of an output I.sub.3 of the third monitor sensor 108 to the output I.sub.1 of the first monitor sensor 106, with reference to the second correspondence table stored in the second correspondence-table storage 120b, and estimates a spectral intensity distribution P(.lamda.) based on the selected relative spectral intensity distribution R(.lamda.), the output I.sub.2 of the second monitor sensor 107 and the output I.sub.20 corresponding to the relative spectral intensity distribution R(.lamda.) in the second correspondence table. A specific method of calculating the spectral intensity distribution P(.lamda.) is described later.

The controller 101 controls emission timings and emission periods of the emission-line light source 102 and the incandescent light source 103.

The emission-line light source 102 is formed, for example, by a visible laser diode (semiconductor laser) for emitting a visible laser beam and outputs emission lines which are a light having a specified wavelength (emission-line wavelength). The incandescent light source 103 is formed, for example, by an incandescent light bulb and outputs a white light having a plurality of wavelengths.

The diffusing plate 104 diffuses an output light from the emission-line light source 102 and the one from the incandescent light source 103.

The collimating optical system 105 collects and converges the output light from the emission-line light source 102 and the one from the incandescent light source 103 diffused by the diffusing plate 104 into parallel lights.

The first, second and third monitor sensors 106, 107, 108 include silicon photodiodes 106a, 107a, 108a and glass filters 106b, 107b, 108b, respectively.

The first monitor sensor 106 monitors an output wavelength of the output light from the emission-line light source 102 diffused by the diffusing plate 104, wherein the glass filter 106b has such a spectral sensitivity as to rise near the output wavelength of the emission-line light source 102.

The second monitor sensor 107 monitors the output wavelength of the light emitted from the emission-line light source 102 diffused by the diffusing plate 104, wherein the glass filter 107b has such a spectral sensitivity as to fall near the output wavelength of the emission-line light source 102.

The third monitor sensor 108 monitors the output wavelength of the light emitted from the incandescent light source 103 diffused by the diffusing plate 104.

FIG. 2 is a graph showing a relative spectral intensity of the calibration light source and spectral transmittances of the filters of the monitor sensors, wherein vertical axis represents relative spectral intensity and spectral transmittance, and horizontal axis represents wavelength.

As shown in FIG. 2, the emission-line light source 102 emits a monochromatic light having an output wavelength .lamda..sub.LD of about 650 nm. The output wavelength has an individual difference of at maximum .+-.5 nm and has a large temperature dependence. Thus, the output wavelength of the emission-line light source 102 is monitored by the first and second monitor sensors 106, 107. Similarly, the spectral intensity distribution and the radiation intensity of the incandescent light source 103 have individual differences and change with time. Thus, the relative spectral intensity distribution of the output light of the incandescent light source 103 is monitored by the first, second and third sensor monitors 106, 107, 108.

An R-64 filter produced by Hoya Optics and having a spectral transmittance shown by R64 in FIG. 2 is, for example, used as the glass filter 106b of the first monitor sensor 106. This glass filter 106b has such a spectral transmittance as to rise near 650 nm which is the output wavelength of the emission-line light source 102. A HA-30 filter produced by Hoya Optics and having a spectral transmittance shown by HA30 in FIG. 2 is, for example, used as the glass filter 107b of the second monitor sensor 107. This glass filter 107b has such a spectral transmittance as to fall near 650 nm which is the output wavelength of the emission-line light source 102. Accordingly, the ratio I.sub.1/I.sub.2 of the output I.sub.1 of the first monitor sensor 106 to the output I.sub.2 of the second monitor sensor 107 decreases when the output wavelength .lamda..sub.LD is shifted toward a shorter wavelength side while increasing when it is shifted toward a longer wavelength side. Particularly in this embodiment, since a curve R64 representing a characteristic of the spectral transmittance of the glass filter 106b suddenly rises as shown in FIG. 2, the glass filter 106b has a high sensitivity to a wavelength shift. The first correspondence table showing the correspondence between the ratio I.sub.10/I.sub.20 of the output I.sub.10 of the first monitor sensor 106 to the output I.sub.20 of the second monitor sensor 107 and the output wavelength .lamda..sub.m of the emission-line light source 102 is stored in the storage 120. The controller 101 calculates the ratio I.sub.1/I.sub.2 of the output I.sub.1 of the first monitor sensor 106 to the output I.sub.2 of the second monitor sensor 107 and calculates an estimated value .LAMBDA..sub.LD of the output wavelength of the emission-line light source 102 based on the calculated ratio I.sub.1/I.sub.2 with reference to the first correspondence table.

Changes in the spectral intensity distribution of the output light of the incandescent light source 103 include changes in the relative spectral intensity distribution and those in the radiation intensity. In order to monitor the relative spectral intensity distribution, a BG-39 filter produced by Hoya Optics and having a spectral transmittance shown by BG39 in FIG. 2 is, for example, used as the glass filter 108b of the third monitor sensor 108. This glass filter 108b has such a spectral transmittance as to peak near 390 nm.

The relative spectral intensity distribution R(.lamda.) of the output light of the incandescent light source 103 depends on the color temperature of a filament of the incandescent light bulb. Specifically, the relative spectral intensity distribution R(.lamda.) is expressed by a characteristic curve R1 shown in FIG. 2 in the case of a color temperature of 2700 (Kelvin), by a characteristic curve R2 shown in FIG. 2 in the case of a color temperature of 2800 (Kelvin), and by a characteristic curve R3 shown in FIG. 2 in the case of a color temperature of 2900 (Kelvin). Since the ratio I.sub.3/I.sub.1 of the output I.sub.3 of the third monitor sensor 108 to the output I.sub.1 of the first monitor sensor 106 changes in relation to the relative spectral intensity distribution R(.lamda.), the radiation spectral intensity distribution of the incandescent light source 103 during the calibration can be estimated based on this ratio I.sub.3/I.sub.1. The second correspondence table showing the correspondence between the relative spectral intensity distributions R(.lamda.) when the incandescent light source 103 of the calibration light source 100 is turned on at a plurality of different color temperatures, the corresponding ratios I.sub.30/I.sub.10 of the outputs 130 of the third monitor sensor 108 to the outputs I.sub.10 of the first monitor sensor 106, and the corresponding outputs I.sub.20 of the second monitor sensor 107 is stored in the storage 120. The controller 101 calculates the ratio I.sub.3/I.sub.1 of the output I.sub.3 of the third monitor sensor 108 to the output I.sub.1 of the first monitor sensor 106, and estimates the relative spectral intensity distribution R(.lamda.) at the time of calibrating the output light of the incandescent light source 103 based on the calculated ratio I.sub.3/I.sub.1 with reference to the second correspondence table. Then, the controller 101 calculates the spectral intensity distribution P(.lamda.) based on the estimated relative spectral intensity distribution R(.lamda.), the output I.sub.2 of the second monitor sensor 107 at the time of calibrating the output light of the incandescent light source 103, and the output I.sub.20 of the second monitor sensor 107 stored beforehand in the storage 120 in accordance with following equation (1): P(.lamda.)=R(.lamda.)I.sub.2/I.sub.20 (1)

As shown in FIG. 2, the second monitor sensor 107 has a sensitivity over the entire visible range (380 to 780 nm) measurable by the spectral luminometer, and suited to monitoring the radiation intensity.

The aforementioned method for monitoring the spectral intensity distribution of the incandescent light source 103 premises that the change in the relative spectral intensity distribution R(.lamda.) of the incandescent light source 103 depends only on the color temperature of the filament. Specifically, this premise holds for the changes in the relative spectral intensity distribution R(.lamda.) caused by the thinning of the filament of the incandescent light source 103 and a change in an applied voltage, but it does not hold for the changes in the relative spectral intensity distribution R(.lamda.) caused by the deposition of the filament on the bulb and the yellowing of the diffusing plate 104. In other words, since the relative ratios of the outputs I.sub.1, I.sub.2, I.sub.3 of the three monitor sensors 106, 107, 108 do not change as long as the above premise holds, the ratio I.sub.20/I.sub.10 of the output I.sub.20 of the second monitor sensor 107 to the output I.sub.10 of the first monitor sensor 106 at the time of setting is further stored in the storage 120 while being related to the relative spectral intensity distribution R(.lamda.) of the second correspondence table. The controller 101 can monitor an abnormality of the incandescent light source 103 by calculating the ratio I.sub.2/I.sub.1 of the output 12 of the second monitor sensor 107 to the output I.sub.1 of the first monitor sensor 106 and confirming that the calculated ratio I.sub.2/I.sub.1 has not changed from the ratio I.sub.20/I.sub.10 at the time of setting, which ratio is stored in the storage 120 beforehand.

Referring back to FIG. 1, the temperature sensor 109 is formed, for example, by a thermistor and compensates for the temperatures of the first, second and third monitor sensors 106, 107, 108. The temperature sensor 109 measures the temperatures of the first, second and third monitor sensors 106, 107, 108. The spectral transmittances of the glass filters 106b, 107b, 108b of the respective monitor sensors 106, 107, 108 have a temperature dependency. For example, the rise of the spectral transmittance of the glass filter 106b is shifted toward the longer wavelength side by slightly over 0.1 nm/C.degree.. In order to compensate for errors caused by the temperature changes of the glass filters 106b, 107b, 108b, a plurality of first correspondence tables and a plurality of second correspondence tables are prepared for different temperatures of the monitor sensors 106, 107, 108. Thus, the controller 101 refers to the first correspondence table and the second correspondence table corresponding to the temperatures of the monitor sensors 106, 107, 108 measured by the temperature sensor 109.

It should be noted that the first, second and third monitor sensors 106, 107, 108 and the temperature sensor 109 are provided in an aluminum block 110.

FIG. 3 is a diagram showing the collimating optical system 105 and the monitor sensors 106 to 108 of the calibration light source 100 when viewed from the diffusing plate 104. As shown in FIG. 3, when the collimating optical system 105 and the monitor sensors 106 to 108 are viewed from the diffusing plate 104, the aluminum block 110 is disposed below the collimating optical system 105. In the aluminum block 110, the second monitor sensor 107 is placed below the collimating optical system 105; the first monitor sensor 106 is placed at the left side of the second monitor sensor 107; the third monitor sensor 108 is placed at the right side of the second monitor sensor 107; and the temperature sensor 109 is placed below the second monitor sensor 107.

Referring back to FIG. 1, the spectral luminometer 200 to be calibrated includes a controller 201, a converging optical system 202, a diaphragm 202, a condenser lens 204, a light receiving unit 205 and a storage 220.

The storage 220 is formed, for example, by an EEPROM and functions as a third correspondence-table storage 220a, a wavelength change amount storage 220b and a sensitivity correction coefficient storage 220c.

The third correspondence-table storage 220a stores a third correspondence table showing a correspondence of the output wavelengths .lamda..sub.m and output ratios Q.sub.n/Q.sub.n+2 corresponding to the emission-line wavelengths. The third correspondence table is described later.

The wavelength change amount storage 220b stores a difference between the wavelength of the emission-line output and the emission-line wavelength estimated by the output wavelength estimator 101a as a wavelength change amount. This wavelength change amount is used for the wavelength calibration at the time of a measurement by the spectral luminometer 200.

The sensitivity correction coefficient storage 220c stores ratios q.sub.n/Q.sub.n of estimated outputs qn to be obtained from the respective light receiving sensors S.sub.n calculated based on the spectral intensity distribution P(.lamda.) estimated by the spectral intensity distribution estimator 101b and the spectral sensitivities of the respective light receiving sensors S.sub.n obtained from the spectral luminometer 200 to outputs Q.sub.1 actually obtained from the light receiving sensors S.sub.n as sensitivity correction coefficients. The sensitivity correction coefficients are used for the sensitivity calibration at the time of a measurement by the spectral luminometer 200.

The controller 201 is formed, for example, by a CPU and functions as an output wavelength calculator 201a and a tristimulus value calculator 201b.

The output wavelength calculator 201a selects a ratio Q.sub.n/Q.sub.n+2 closest to "1" from three output ratios Q.sub.n/Q.sub.n+2 in the case of measuring the emission-line wavelength of the calibration light source 100, and calculates a wavelength .lamda..sub.m corresponding to the selected ratio Q.sub.n/Q.sub.n+2 with reference to the third correspondence table stored in the third correspondence storage 220a.

The tristimulus value calculator 201b corrects weight coefficients according to the wavelength change amount and calculates tristimulus values using the corrected weight coefficients in the case of calculating the tristimulus values by a sum product of the outputs of the light receiving sensors S.sub.n at each measurement wavelength and the weight coefficients for each measurement wavelength.

The converging optical system 202 converges the light collimated by the collimating optical system 105 of the calibration light source 100 to an opening of the diaphragm 203.

The diaphragm 203 specifies a receiving angle of a measurement beam together with the converging optical system 202.

The condenser lens 204 collects the light having passed through the diaphragm 203 to an incident slit of the light receiving unit 205.

The light receiving unit 205 includes a diffraction grating for dispersing the incident light according to the wavelength, and a light receiving sensor array in which a plurality of photoelectric conversion elements (light receiving sensors S.sub.n) for receiving the light dispersed in different directions at the respective wavelengths by the diffraction grating and outputting electrical signals corresponding to the light intensities of the respective wavelength components of the received light are arrayed.

At the time of a calibration, a housing 111 of the calibration light source 100 and a housing 206 of the spectral luminometer 200 are coupled by connecting an opening 111a formed in the housing 111 and an opening 206a formed in the housing 206 in order to prevent the entrance of an external light.

The system control unit 300 is formed, for example, by a CPU and functions as a wavelength calibrator 300a, a sensitivity calibrator 300b, a stray-light level estimator 300c and a half-width estimator 300d.

The wavelength calibrator 300a corrects the wavelength by estimating the wavelength of the emission-line output based on the ratios of the outputs from the light receiving sensors S.sub.n at a plurality of measurement wavelengths neighboring the emission-line wavelength, calculating the wavelength change amount based on the estimated wavelength of the emission-line output and a known emission-line wavelength, and storing the calculated wavelength change amount in the storage 220 of the spectral luminometer 200 in the case that the spectral luminometer 200 measures the emission-line output of the calibration light source 100.

The sensitivity calibrator 300b calibrates the sensitivity of the spectral luminometer 200 by calculating the estimated outputs q.sub.n to be obtained from the respective light receiving sensors S.sub.n based on the spectral intensity distribution P(.lamda.) estimated by the spectral intensity distribution estimator 101b and the spectral sensitivities of the respective light receiving sensors S.sub.n obtained from the spectral luminometer 200, calculating the ratio q.sub.n/Q.sub.n of the calculated estimated output I.sub.1 to the output I.sub.1 actually obtained from the light receiving sensor S.sub.n for each light receiving sensor S.sub.n, and storing the calculated ratios q.sub.n/Q.sub.n in the storage 220 of the spectral luminometer 200 in the case that the spectral luminometer 200 measures the emission-line output of the calibration light source 100.

The stray-light level estimator 300c estimates a change in the stray-light level of the spectral luminometer 200 by calculating ratios of the intensities of the emission lines obtained based on the outputs from the respective light receiving sensors S.sub.n at a plurality of measurement wavelengths neighboring the emission-line wavelength to the outputs of the light receiving sensors S.sub.n at a wavelength where the light receiving sensors S.sub.n have no sensitivity to the emission-line wavelength (outputs of the light receiving sensors S.sub.n having a spectral sensitivity of 0 at the emission-line wavelength), and comparing the calculated ratios with initial values of the ratios stored beforehand.

The half-width estimator 300d estimates a change in the half-width of the spectral luminometer 200 by calculating the half-widths of the light receiving sensors S.sub.n near the emission-line wavelength based on the outputs of the light receiving sensors S.sub.n at a plurality of measurement wavelengths neighboring the emission-line wavelength and comparing the calculated half-widths with initial values of the half-widths stored beforehand.

The wavelength recalibration of the spectral luminometer 200 is described. The spectral luminometer 200 measures a light emitted from the emission-line light source 102 of the calibration light source 100 upon receiving an instruction from the system control unit 300.

FIG. 4 is a graph showing relative spectral sensitivities of five light receiving sensors S.sub.n (n=48 to 52) at the emission-line wavelength of the emission-line light source 102 and wavelengths neighboring the emission-line wavelength. As described above, the output wavelength of the emission-line light source 102 varies within a range of 650.+-.5 nm. In FIG. 4, three emission-line wavelengths .lamda..sub.LD1, .lamda..sub.LD2, .lamda..sub.LD3 are shown. For example, in the case that the output wavelength .lamda..sub.LD of the emission-line light source 102 of the calibration light source 100=.lamda..sub.LD1, the spectral sensitivity of the light receiving sensor S.sub.48 neighboring at the shorter wavelength side falls near .lamda..sub.LD1, whereas the spectral sensitivity of the light receiving sensor S.sub.50 neighboring at the longer wavelength side rises near .lamda..sub.LD1. Thus, a ratio Q.sub.48/Q.sub.50 of an output (Q.sub.48).sub.1 of the light receiving sensor S.sub.48 to an output (Q.sub.50).sub.1 of the light receiving sensor S.sub.50 increases at a high sensitivity if the output wavelength .lamda..sub.LD is shifted toward the shorter wavelength side while decreasing at a high sensitivity if it is shifted toward the longer wavelength side. Accordingly, the controller 201 of the spectral luminometer 200 calculates the ratio Q.sub.48/Q.sub.50 of the output (Q.sub.48).sub.1 of the light receiving sensor S.sub.48 to the output (Q.sub.50).sub.1 of the light receiving sensor S.sub.50, estimates the output wavelength .lamda..sub.LD of the emission-line light source 102 with reference to the third correspondence table stored in the storage 220, and outputs the estimated output wavelength .lamda..sub.LD to the system control unit 300. The system control unit 300 corrects the output wavelength by calculating a wavelength change amount d.lamda.=.lamda..sub.LD-.LAMBDA..sub.LD of the light receiving unit 205 of the spectral luminometer 200 based on a difference between the estimated value .lamda..sub.LD inputted from the controller 201 of the spectral luminometer 200 and an estimated value .LAMBDA..sub.LD of the emission-line wavelength inputted from the controller 101 of the calibration light source 100 and storing it in the storage 220 as a common correction amount for the spectral sensitivities of the respective light receiving sensors S.sub.n of the light receiving unit 205 of the spectral luminometer 200.

The spectral sensitivities of two of a plurality of light receiving sensors S.sub.n (n=48 to 52) for calculating the ratio preferably sharply change in opposite directions at the output wavelength .lamda..sub.LD Of the emission-line light source 102, and the combination of the two light receiving sensors differs depending on the position of the output wavelength .lamda..sub.LD. Specifically, in the case that the output wavelength .lamda..sub.LD of the emission-line light source 102 of the calibration light source 100=.lamda..sub.LD2 in FIG. 4, it is preferable to calculate a ratio Q.sub.49/Q.sub.51 of an output (Q.sub.49).sub.1 of the light receiving sensor S.sub.49 to an output (Q.sub.51).sub.1 of the light receiving sensor S.sub.50. In the case that the output wavelength .lamda..sub.LD of the emission-line light source 102 of the calibration light source 100=.lamda..sub.LD3 in FIG. 4, it is preferable to calculate a ratio Q.sub.50/Q.sub.52 of the output (Q.sub.50).sub.1 of the light receiving sensor S.sub.50 to an output (Q.sub.52).sub.1 of the light receiving sensor S.sub.52. Thus, three ratios Q.sub.48/Q.sub.50, Q.sub.49/Q.sub.51, Q.sub.50/Q.sub.52 corresponding to the respective emission-line wavelengths are prepared in the third correspondence table stored in the storage 220, and the output wavelength .lamda..sub.LD of the emission-line light source 102 is estimated using a most suitable one of the calculated ratios Q.sub.48/Q.sub.50, Q.sub.49/Q.sub.51, Q.sub.50/Q.sub.52 at the time of the calibration. Specifically, the controller 201 estimates the output wavelength .lamda..sub.LD of the emission-line light source 102 using the ratio closest to "1" among the three ratios Q.sub.48/Q.sub.50, Q.sub.49/Q.sub.51, Q.sub.50/Q.sub.52.

Next, the recalibration of the spectral sensitivity of the spectral luminometer 200 is described. After the output wavelength is recalibrated as above, the spectral luminometer 200 measures an output light of the incandescent light source 103 of the calibration light source 100 upon receiving an instruction from the system control unit 300. The spectral luminometer 200 sends the output (spectral sensitivities) Q(.lamda.) of the light receiving unit 205 at each wavelength to the system control unit 300. The system control unit 300 corrects the spectral sensitivity of the spectral luminometer 200 by calculating the outputs q.sub.1 estimated to be obtained from the respective light receiving sensors S.sub.n based on the spectral intensity distribution P(.lamda.) inputted from the controller 101 of the calibration light source 100, the spectral sensitivities Q(.lamda.) of the respective light receiving sensors S.sub.n of the light receiving unit 205 inputted from the controller 201 of the spectral luminometer 200 and the aforementioned wavelength change amount d.lamda., calculating the ratio q.sub.n/Q.sub.n of the calculated estimated output q.sub.1 to the actually measured value Q.sub.n for each light receiving sensor S.sub.n, and storing the calculated ratios q.sub.n/Q.sub.n in the controller 201 of the spectral luminometer 200.

For the calibration of the output wavelength and the spectral sensitivity of the spectral luminometer 200, the correspondence table for monitoring the output wavelength of the emission-line light source 102 (first correspondence table) and the correspondence table for monitoring the radiation light of the incandescent light source 103 (second correspondence table) need to be set beforehand in the calibration light source 100, and the correspondence table for the wavelength calibration (third correspondence table) needs to be set in the spectral luminometer 200. Procedures of setting these correspondence tables are described below.

First, the procedure of setting the first correspondence table in the calibration light source 100 is described. FIG. 5 is a diagram showing the calibration system for the spectral luminometer in setting the first correspondence table in the calibration light source 100. The calibration system of the spectral luminometer shown in FIG. 5 is provided with the calibration light source 100, a reference monochrometer 303 and the system control unit 300.

The reference monochrometer 303 includes a light splitting unit having the wavelength thereof calibrated by mercury emission lines or the like, and a light source unit, and projects a monochromatic light having a desired wavelength toward the calibration light source 100.

The system control unit 300 causes the reference monochrometer 303 to emit a plurality of monochromatic lights having wavelengths near the output wavelength of the emission-line light source 102 at an interval of a specified wavelength to make the monochromatic lights incident on the opening 111a formed in the housing 111 of the calibration light source 100. In this embodiment, the system control unit 300 causes the reference monochrometer 303 to emit monochromatic lights having wavelengths of 644 nm to 656 nm near the output wavelength of 650 nm of the emission-line light source 102 at an interval of 2 nm. The monochromatic lights incident on the calibration light source 100 are incident on the diffusing plate 104 after passing through the collimating optical system 105. The lights diffused and reflected by the diffusing plate 104 are detected by the first and second monitor sensors 106, 107. The system control unit 300 obtains the outputs I.sub.1, I.sub.2 of the first and second monitor sensors 106, 107 corresponding to the respective monochromatic lights which are inputted from the controller 101 of the calibration light source 100, and calculates the ratios I.sub.1/I.sub.2 of the outputs I.sub.1, I.sub.2. The system control unit 300 generates the first correspondence table by relating the calculated ratios I.sub.1/I.sub.2 to the wavelengths .lamda..sub.m of the monochromatic lights.

The aluminum block 110 in which the first to third monitor sensors 106, 107, 108 and the temperature sensor 109 are placed can be exposed by detaching a lid 111b (see FIG. 3) at the bottom of the housing 111 of the calibration light source 100. A constant-temperature unit 301 controlled by the control system unit 300 is closely attached to this exposed aluminum block 110, thereby controlling the temperatures of the first to third monitor sensors 106, 107, 108. The temperatures of the first to third monitor sensors 106, 107, 108 are detected by the temperature sensor 109. The system control unit 300 sets a plurality of temperatures T1, T2, T3 in the aluminum block 110 by controlling the constant-temperature unit 301 and obtains the outputs I.sub.1, I.sub.2 at the respective temperatures. In this embodiment, the system control unit 300 sets the temperature in the aluminum block 110 approximately at T1=13.degree. C., T2=23.degree. C., T3=33.degree. C. and obtains the outputs I.sub.1, I.sub.2. Simultaneously, the temperature sensor 109 detects the temperatures T1, T2, T3 of the first and second monitor sensors 106, 107 and outputs the detected temperatures T1 , T2 , T3 to the controller 101. The system control unit 300 obtains the detected temperatures T1, T2, T3 from the controller 101, generates the first correspondence table by relating the outputs I.sub.1, I.sub.2 to the wavelengths .lamda..sub.m of the monochromatic lights for each temperature, and stores the generated first correspondence table in the storage 120 of the calibration light source 100. TABLE-1 below shows an example of the first correspondence table generated as above.

TABLE-US-00001 TABLE 1 Wavelength of Monochromatic Light .lamda..sub.m 644 nm 646 nm 648 nm 650 nm 652 nm 654 nm 656 nm I.sub.10/I.sub.20 T.sub.1 (I.sub.10/I.sub.20).sub.11 (I.sub.10/I.sub.20).s- ub.12 (I.sub.10/I.sub.20).sub.13 (I.sub.10/I.sub.20).sub.14 (I.sub.10/I.su- b.20).sub.15 (I.sub.10/I.sub.20).sub.16 (I.sub.10/I.sub.20).sub.17 T.sub.2 (I.sub.10/I.sub.20).sub.21 (I.sub.10/I.sub.20).sub.22 (I.sub.10/I- .sub.20).sub.23 (I.sub.10/I.sub.20).sub.24 (I.sub.10/I.sub.20).sub.25 (I.s- ub.10/I.sub.20).sub.26 (I.sub.10/I.sub.20).sub.27 T.sub.3 (I.sub.10/I.sub.20).sub.31 (I.sub.10/I.sub.20).sub.32 (I.sub.10/I- .sub.20).sub.33 (I.sub.10/I.sub.20).sub.34 (I.sub.10/I.sub.20).sub.35 (I.s- ub.10/I.sub.20).sub.36 (I.sub.10/I.sub.20).sub.37

As shown in TABLE-1, the ratio I.sub.10/I.sub.20 of the output I.sub.10 to the output I.sub.20 is as follows, for example, when the wavelength .lamda..sub.m of the monochromatic light is 644 nm. The ratio I.sub.10/I.sub.20 is (I.sub.10/I.sub.20).sub.11 in the case that the temperature detected by the temperature sensor 109 is T1; the ratio I.sub.10/I.sub.20 is (I.sub.10/I.sub.20).sub.21 in the case that the temperature is T2; and the ratio I.sub.10/I.sub.20 is (I.sub.10/I.sub.20).sub.31 in the case that the temperature is T3. In this way, the system control unit 300 generates the first correspondence table by relating the wavelengths .lamda..sub.m of the monochromatic lights to the outputs I.sub.1, I.sub.2 for each temperature, and stores the generated first correspondence table in the controller 101.

At the time of the calibration, the controller 101 applies interpolation to the ratio I.sub.1/I.sub.2 of the output I.sub.1 to the output I.sub.2 for the temperature T detected by the temperature sensor 109 with reference to the first correspondence table shown in TABLE-1, newly generates a correspondence table of .LAMBDA..sub.LD and I.sub.1/I.sub.2 at the detected temperature T, and applies interpolation to .LAMBDA..sub.LD for I.sub.1/I.sub.2 with reference to the newly generated correspondence table to calculate the estimated value .LAMBDA..sub.LD of the output wavelength corresponding to the monitored ratio I.sub.1/I.sub.2.

Next, the procedure of setting the second correspondence table in the calibration light source 100 is described. FIG. 6 is a diagram showing the calibration system for the spectral luminometer in setting the second correspondence table in the calibration light source 100. The calibration system of the spectral luminometer shown in FIG. 6 is provided with the calibration light source 100, a reference spectral luminometer 302 and the system control unit 300.

The reference spectral luminometer 302 has its output wavelength calibrated by a reference monochrometer and its spectral sensitivity calibrated by a standard light bulb.

The system control unit 300 turns the incandescent light source 103 of the calibration light source 100 at three kinds of drive voltages V.sub.1, V.sub.2, V.sub.3, causes the first to third monitor sensors 106, 107, 108 to detect the radiation beams from the diffusing plate 104, and causes the reference spectral luminometer 302 to measure relative spectral intensity distributions R.sub.1(.lamda.), R.sub.2(.lamda.), R.sub.3(.lamda.) of the beams emerging from the collimating optical system 105. The system control unit 300 obtains the outputs I.sub.10, I.sub.20, I.sub.30 of the first to third monitor sensors 106, 107, 108 from the controller 101 of the calibration light source 100, calculates the ratios I.sub.30/I.sub.10 of the outputs 130 to the outputs I.sub.10 and the ratios I.sub.20/I.sub.10 of the outputs I.sub.20 to the outputs I.sub.10. The system control unit 300 generates the second correspondence table by relating the calculated ratios I.sub.30/I.sub.10, the outputs I.sub.20 and the calculated ratios I.sub.20/I.sub.10 to the relative spectral intensity distributions R.sub.1(.lamda.), R.sub.2(.lamda.), R.sub.3(.lamda.).

The aluminum block 110 in which the first to third monitor sensors 106, 107, 108 and the temperature sensor 109 are placed can be exposed by detaching the lid 111b (see FIG. 3) at the bottom of the housing 111 of the calibration light source 100. The constant-temperature unit 301 controlled by the control system unit 300 is closely attached to this exposed aluminum block 110, thereby controlling the temperatures of the first to third monitor sensors 106, 107, 108. The temperatures