Fundamentals of spectroradiometry and colorimetry János Schanda

Spectroradiometry u Publication CIE : The spectroradiometric measurement of light sources –The spectroradiometer –Basic principles of measurement –Bandwidth considerations

Colorimetry - Division 1 u Publication CIE : Colorimetry –Standard illuminants –Standard observers –Calculation of tristimulus values –Uniform colour spacing u TC 1-36: New chromaticity diagram u TC 1-38: Tabulation of spectral data u Report on Improved Colorimetry

Colorimetry - Division 2 u TC 2-04: Secondary standard sources u TC 2-16: Characterization of the performance of tristimulus colorimeters  TC 2-33, -35: Standard illuminants and V( ) & V’( ) u TC 2-39: Geometric tolerances for colorimetry

Spectroradiometry of LEDs u Spectral irradiance measurement u Spectral radiance and flux measurement u The spectroradiometer u Measurement principles u Practical measurements

Colorimetry of LEDs u Fundamentals of CIE colorimetry u Light source colorimetry u A new system of colorimetry? Reportership: Improved colorimetry u 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 u Light grasp or etendu, throughput, efficiency: u Double monochromator: –Two gratings (additive, subtractive dispersion) –grating + prism

Monochromators - 2 u Stray radiation Determination with –Interference filter: –Sharp cut-off filters –Lasers u Wavelength accuracy: +/- 0,1 nm –stability –temperature dependence: 0,1 - 0,5 nm/C°

Detector and measuring system u Irradiation of detector - homogeneity u Type of detector: photomultiplier, Si-cell –linearity (superposition) –temperature dependence –high voltage stability u Standard sources u Method of measurement

Method of measurement u Sequence: test - standard u Transmittance function - Bandwidth

Bandwidth & sampling

Continuous scan method

Practical measurements - Errors u Stray light u Wavelength error u Bandwidth - interpolation, extrapolation u Polarization u Detector system u Reference standard

Colorimetry u Additive colour mixture

Laws of additive colour matching u Symmetry law: u Transitivity law: u Proportionality law: u Additivity law:

Grassmann’s laws u To specify a colour match three independent variables are necessary and sufficient u For additive mixture of colour stimuli, only their tristimulus values are relevant, not their spectral composition u In additive mixtures of colour stimuli, if one or more components are gradually changed, the resulting tristimulus values also change gradually

Colour equation - 1 u Positive additivity

Colour equation - 2 u External colour mix - negative additivity

Colour equation - 3 u Two spectral lights: u Many spectral lights:

Colour equation - 4 u Integral form: with three t values u Three real primaries with L = 1,000R + 4,5907G + 0,601B

R, G, B colour space

RGB - XYZ transformation

A new system of colorimetry? u TC 1-36: Physiologically significant...

Improved colorimetry? u Luminance-brightness discrepancy u Additivity problems u New colour matching functions? u Individual variations u Highly metameric matches u Colour appearance models

TC 1-36: Physiologically significant... L, M, S primaries based on psychophysical measurements: u König hypothesis - congenital dichromats u Photopigment spectral absorbance u Selective absorption by the lens u Selective absorption by the macular pigment

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