P5Publication 5 P. Manninen and P. Orreveteläinen, "On spectral and thermal behaviors of AlGaInP light-emitting diodes under pulse-width modulation," Appl.

Reaction times are recorded to chromatic, mesopic stimuli to investigate mesopic reaction time spectral sensitivity. Measurements are made using three laboratory setups and a driving simulator. The chromatic stimuli have spectral distributions that range from quasi-monochromatic to broadband. Reaction time spectral sensitivity for small (0.298) foveal stimuli changes little with luminance and is described adequately by V (l). Reaction time spectral sensitivity for peripheral stimuli exhibits a Purkinje shift, and approaches V 0 (l) at 0.01 cd m À2 . In the periphery, the results for medium-sized stimuli (28) reflect the activity of colour-opponent neurons in addition to rod and cone-based achromatic activity, resulting in three-peaked spectral sensitivity functions.

This paper introduces an experimental multitechnique method which was developed to establish a basis for a task performance-based mesopic photometry. This approach considers night-time driving by dividing visual performance into three visual tasks, of which achromatic threshold and reaction time are presented. The performance of both visual tasks decreased with decreasing luminance level from 1 to 0.01 cd m(-2), showing the strong effect of light level on visual performance in driving. The behaviour of the achromatic contrast threshold and reaction time for low-contrast targets was similar in terms of spectral effects, the strongest effects occurring at the lower mesopic levels. Both measures showed the Purkinje shift with decreasing luminance levels. The experimental data were used to calculate mesopic performance measures with the new mesopic model. The results imply that compared with V(lambda), spectral sensitivity in night-time driving can be better described with a mesopic model based on visual performance measures.