CURRENT DEVELOPMENT IN JAPA. Research on tunnel entrance lighting, which has been carried outin Japan during the past decade, is reviewed. Special emphasis is placed on research on a method to derive the so-called adaptation luminance of the observer's eyes for any complex luminance field. Such a method is essential for accurately determining the luminance to beprovided in the threshold zone of the tunnel. The present method isbased on fundamental research on the relationship between the adaptation luminance and the luminance to be provided in the tunnel to make possible perception of possible obstacles. As a representation ofadaptation luminance, the equivalent luminance of the standard field is defined as a uniform luminance of the standard field for which the luminance difference threshold of the observer's eyes is equivalent to that for the complex luminance field. On the basis of research on the effect of the veiling luminance on the luminance differencethresholds (measuring the equivalent veiling luminance at the tunnel site by means of a glare lens and of the road surface to which thedriver's fovea is assumed to be adapted) a method for deriving the equivalent luminance of the standard field for any complex luminancefield has been developed. The method is briefly described.(A)
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