Fundamentals of
spectroradiometry and
colorimetry
János Schanda
Spectroradiometry
 Publication
CIE 63-1984:
The spectroradiometric measurement of
light sources
– The spectroradiometer
– Basic principles of measurement
– Bandwidth considerations
Colorimetry - Division 1
 Publication
–
–
–
–
CIE 15.2-1986: Colorimetry
Standard illuminants
Standard observers
Calculation of tristimulus values
Uniform colour spacing
 TC
1-36: New chromaticity diagram
 TC 1-38: Tabulation of spectral data
 Report on Improved Colorimetry
Colorimetry - Division 2
 TC
2-04: Secondary standard sources
 TC 2-16: Characterization of the
performance of tristimulus colorimeters
 TC 2-33, -35: Standard illuminants and
V(l) & V’(l)
 TC 2-39: Geometric tolerances for
colorimetry
Spectroradiometry of LEDs
 Spectral
irradiance measurement
 Spectral radiance and flux measurement
 The spectroradiometer
 Measurement principles
 Practical measurements
Colorimetry of LEDs
 Fundamentals
of CIE colorimetry
 Light source colorimetry
 A new system of colorimetry?
Reportership: Improved colorimetry
 Work in CIE TC 1-36: Fundamental
chromaticity diagram with
physiologically significant axes
The spectroradiometer system
Input optical arrangement-1
Input optical arrangement-2
Monochromators - 1
 Light
grasp or etendu, throughput,
efficiency:
 (l )  h  A d
Z (l ) 
.
f
dl
 Double
monochromator:
– Two gratings (additive, subtractive
dispersion)
– grating + prism
Monochromators - 2
 Stray
radiation
Determination with
– Interference filter:
– Sharp cut-off filters
– Lasers
 Wavelength
s
R2  T (l )

1
 (l )
R1
accuracy: +/- 0,1 nm
– stability
– temperature dependence: 0,1 - 0,5 nm/C°
Detector and measuring system
 Irradiation
of detector - homogeneity
 Type of detector: photomultiplier, Si-cell
– linearity (superposition)
– temperature dependence
– high voltage stability
 Standard
sources
 Method of measurement
Method of measurement
 Sequence:
test - standard
 Transmittance function - Bandwidth
Bandwidth & sampling
Continuous scan method
Practical measurements - Errors
 Stray
light
 Wavelength error
 Bandwidth - interpolation, extrapolation
 Polarization
 Detector system
 Reference standard
Colorimetry
 Additive
colour mixture
Laws of additive colour
matching
 Symmetry
law:
If A  B then B  A
 Transitivity law:
If A  B and B  C then A  C
 Proportionality law:
If A  B then  A   B
 Additivity
law:
If A  B, C  D, or A  C  B  D
then A  D  B  C
Grassmann’s laws
 To
specify a colour match three independent
variables are necessary and sufficient
 For additive mixture of colour stimuli, only
their tristimulus values are relevant, not
their spectral composition
 In additive mixtures of colour stimuli, if one
or more components are gradually changed,
the resulting tristimulus values also change
gradually
Colour equation - 1
Positive
additivity
C  R  R  G  G  B  B
Colour equation - 2
 External
colour mix - negative additivity
C  R  R  G  G  B  B
Colour equation - 3
 Two
spectral lights:
C(l 1)  C(l 2)   R1  R2  R  G1  G2  G   B1  B2  B
 Many
spectral lights:
Rk
Gk
Bk
780 nm
 P(l )
380 nm
780 nm
 P(l )
380 nm
780 nm
 P(l )
380 nm
r ( l ) l
g ( l ) l
b ( l ) l
Colour equation - 4
 Integral
form:
780nm
Ti  k
 el ti (l ) dl ,
380nm
with three t values
 Three real primaries with
L = 1,000R + 4,5907G + 0,601B
R, G, B colour space
RGB - XYZ transformation
X
Y
Z
2 ,76888 1,75175
 1,00000
113016
,
R
4 ,59070 0,06010  G
0,00000 0,05651 5,59427
...
B
1,80
1,60
1,40
x2(lambda)
rel. sens.
1,20
1,00
y2(lambda)
0,80
z2(lambda)
0,60
0,40
0,20
0,00
350
400
450
500
550
600
650
wavelength, nm
700
750
800
850
A new system of colorimetry?
 TC
1-36: Physiologically significant ...
1
log cone action sensitivity
0
-1
-2
L-cone
-3
M-cone
-4
S-cone
-5
-6
-7
-8
350
450
550
wavelength, nm
650
750
Improved colorimetry?
 Luminance-brightness
 Additivity
discrepancy
problems
 New colour matching functions?
 Individual variations
 Highly metameric matches
 Colour appearance models
TC 1-36: Physiologically significant
...
L, M, S primaries based on
psychophysical measurements:
 König hypothesis - congenital dichromats
 Photopigment spectral absorbance
 Selective absorption by the lens
 Selective absorption by the macular
pigment
Thanks for your attention