Rotating disc visibility meter: Novel design

Abstract

A novel contrast reducing visibility meter is presented, based on luminance combination by twin rotating discs. The discs are painted in diffusing white and are illuminated by an internal adjustable veiling source so as to decrease the task luminance and simultaneously to serve as a veiling light screen. Light rays enter and leave through a narrow periscope placed on top of the box containing the system and the observer is placed at a distance from the periscope. In this way the instrument reduces the visual field as little as possible and the influence of all possible sources of glare in the visual field is considered.