While light intensity is the measurable require in the ECE Regulations, this provides no information on how brightness affects an observer. The brightness of a signal lamp is described by its luminance, which is the light intensity relative to an illuminated area. The luminance of rear lights and brake lights was investigated under nighttime conditions using a road simulation evaluated by five observers rating their subjective impression. Up to a distance of 77m to the rear, the luminance was the characteristic factor. Optimum luminances were determined for rear- and brake lights. The possibility is considered that rear- and brake lights will not be reliably distinguishable, especially as new light sources are introduced. For the covering abstract see ITRD E123380.
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