In night-time driving, the adaptation luminance is between 0.1 cd/m2 (at 60-70m from the car) and 5-7 cd/m2 (closely in front of the car). Therefore, drivers have to adapt to mesopic conditions. But since the beginning of the 20th century, photometry for automobile applications has been based on the V(lambda)-function. This is only usable in the photopic range higher than 10-50 cd/m2. ECE and SAE-regulations are based on V(lambda)-photometry, independent of the type of light source used. This photometric system (i.e. the quantity of photopic luminance) is unable to assess lights in terms of perceived brightness (especially in the mesopic range) due to a number of visual mechanisms (the chromatic mechanisms and the rod mechanism) that are not incorporated in the definition of V(lambda). This effect is often referred to as the brightness-luminance discrepancy. This means that two different coloured lights of the same luminance do not always look equally bright. There are two reasons for this: 1. chromatic contribution to brightness (Helmholtz-Kohlrausch effect); 2. contribution of the rod photoreceptors (Purkinje effect). At mesopic luminance levels between 0.1 and 1.5 cd/m2, an HID Xenon lamp (x=0.40; y=0.41; TC=3500K) required about 5-10% less photopic luminance than an incandescent lamp (H7: x=0.43; y=0.41; TC=3100K) to match in perceived brightness (depending on the luminance level). The white LED lamp (x=0.30; y=0.28; TC=6500K) required about 20% less photopic luminance. Thus the tendency is that if the correlated colour temperature is higher (i.e. the light source provides more bluish light) then the light source looks brighter than predicted by its value of photopic luminance. The perceived brightness of the illuminated mesopic scene is an important parameter for night-time traffic because it is related to the activity level of visual detection and visual search mechanisms. Therefore, it is important to consider this result for the design of automotive front lighting light sources. As seen from the inter-observer variability analysis, there exist at least two clusters of observers whose mesopic brightness perception is different. The CIE supplementary system of photometry (works reasonably well only for the observers of Cluster 1.
Brightness appearance of automotive front lighting light sources - a series of visual experiments
2009
7 Seiten, 5 Bilder, 3 Quellen
Conference paper
English
LIGHT GUIDE UNIT WITH PATTERN STRUCTURE FOR UNIFORMITY BRIGHTNESS OF AUTOMOTIVE LIGHTING GRILLE
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