The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
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Effects of Lighting Parameters on Contrast Threshold in the Mesopic and Photopic Luminance Ranges

Jaakko Ketomäki

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Department of Electrical and Communications Engineering for public examination and debate in Auditorium S3 at Helsinki University of Technology (Espoo, Finland) on the 5th of October, 2006, at 12 noon.

Dissertation in PDF format (ISBN 951-22-8334-4)   [1817 KB]
Dissertation is also available in print (ISBN 951-22-8333-6)

Abstract

The first objective of this thesis was to find out how the background luminance level, spectra of the background and stimulus, and eccentricity of the stimulus affect contrast thresholds in the mesopic luminance range. The background luminance levels used were between LB=0.01…20 cd/m2. They cover the typical luminance levels of road lighting. The spectra of the background and stimulus were broadband white, blue, green, and red. The measurements were made at eccentricities of 0 and 10°. The results of this thesis confirmed that when the photopic background luminance level decreases from LB=10 cd/m2 to LB=0.01 cd/m2 the contrast threshold increases at stimulus eccentricities of both 0 and 10°. It was found that the contrast threshold increased the least with blue and the most with red background spectra when the background and stimulus had the same spectrum. When the background was white, the contrast threshold increased the least with blue and the most with red stimulus spectra. The results show that the spectral sensitivity of the eye is shifted towards shorter wavelengths when photopic background luminance levels are reduced from LB=10 to LB=0.01 cd/m2.

The second objective was to find out the differences in the contrast threshold when a white or coloured background spectrum was used. It was found that the differences between the contrast thresholds measured with different stimuli and background spectra were larger when the measurements were taken with a coloured stimulus and a white background.

The measured contrast thresholds were applied to existing models for mesopic spectral sensitivity. The goal was to find out if the models describe the mesopic contrast threshold in the same way for different stimulus and background spectra. The models used were Palmer's model [Palmer 1968], the X model [Rea et al 2004], and the MOVE model [Eloholma and Halonen 2005]. It was found that all the models used describe the spectral sensitivity at an eccentricity of 10° at the photopic background luminance levels LB=0.01…10 cd/m2 better than the photopic spectral luminous efficiency function V(λ), when contrast threshold is used as a visual task. It was found that the MOVE model describes the mesopic contrast threshold best at the photopic background luminance levels LB=0.01…3 cd/m2 when a white background and a coloured stimulus were used.

Keywords: contrast threshold, mesopic vision, peripheral vision, mesopic spectral sensitivity, models for mesopic vision

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© 2006 Helsinki University of Technology

Last update 2011-05-26