Abstract
Atmospheric straylight (haze, exhaust smoke), similar to straylight from the eye or the windscreen, causes a luminous veil that especially deteriorates the visibility of details in relatively dark scenes like tunnel entrances. This phenomenon influences therefore the required light level in the tunnel entrance. The magnitude of atmospheric straylight has been measured for widely varying conditions of meteorological visibility and ambient lighting. See Part I PB 27787 and Part III PB 24311.