Effect of chromatic mechanisms on the detection of mesopic incremental targets at different eccentricities.

Spectral sensitivity functions for the threshold detection of mesopic incremental targets were compared for different target eccentricities (10, 20, and 30 degrees ) and for different mesopic backgrounds (0.1, 0.5 and 1.0 cd m(-2)). Relative responsivities of achromatic mechanisms (L + M and rods) and chromatic mechanisms (S and /L-M/) were estimated for each eccentricity and background. Chromatic mechanisms contribute significantly to detection but their effect is lower at 30 degrees . A new contrast metric (C(CHC2)) is introduced to account for the selective adaptation of the photoreceptors and the effects of the chromatic mechanisms i.e. broadening of the range of spectral sensitivity with multiple local maxima and yellow sub-additivity of detection performance. The C(CHC2) metric is compared with the achromatic contrast metric of the MOVE model (C(MOVE)). For the same target, C(CHC2) generally predicts a higher visibility level than C(MOVE). However, in accordance with visual observations, for grey or yellowish incremental targets appearing at the eccentricities of 20 and 30 degrees , the visibility predicted by C(CHC2) is less than the visibility predicted by C(MOVE).

Spectral discomfort glare sensitivity investigations.

The main concern of car headlamp manufacturers is to provide better visibility. Unfortunately, by increasing the luminous intensity of the headlamp, the risk of increasing discomfort glare for the other road users increases. One possibility to increase visibility and decrease glare could be the selection of a spectral power distribution for the headlamp such that it emits in wavelength regions (if such wavelengths exist) where luminous sensitivity is high, and glare sensitivity is low. For this the spectral discomfort glare sensitivity of humans under low photopic conditions has to be determined. Spectral discomfort glare sensitivity was determined using ten young observers, requesting the observers to select medium glare settings of monochromatic radiations based on the de Boer glare rating scale, both at near-foveal and 10 degrees extra-foveal directions of the 2 degrees diameter glare source. It was found that the spectral discomfort glare sensitivity function could not be described by a simple addition of the photopic spectral luminous efficiency function and the short wavelength cone fundamental, but that the contribution of the chromatic channels of human vision may also have to be considered.

Matrix-based color measurement corrections of tristimulus colorimeters.

For colorimetric imaging the tristimulus technique is still the best practical method to keep the measurement time within reasonable limits. However, the achievable color measurement uncertainties for special sources can be large. It is described how the systematic errors can be significantly reduced by using matrix-based color corrections and how the matrix elements can be optimized to obtain the smallest spectral mismatch errors for different light-source distributions. An approach for decreasing the systematic errors is to increase the number of the colorimeter channels (or filters) used for a measurement. Using five channels in a colorimeter is an optimum choice. Determination of the optimum matrices for the five channels is discussed. The correction matrices are designed such that the spectral mismatch errors of the realized functions are minimized relative to the CIE standard color matching functions for several selected test-source distributions. The optimum matrix depends on the (test) light source to be measured. Adaptive matrix values are determined by using the channel outputs and the spectral power distribution of color LEDs approximated with a simple approximation function. The systematic errors are evaluated for a number of colored and white LEDs. The noise propagation with the applied matrix corrections is investigated.