A New Scale of Relative Footcandles for the Luckiesh-Moss Visibility Meter

It is highly desirable to develop a means by which any visual task, regardless of its complexity, may be evaluated and its degree of supra-threshold visibility with a specific illumination may be appraised. Such a method should make it possible to determine the footcandle-level necessary to raise the visibility of the task to a desired supra-threshold value. A device which permits one to achieve these objectives is the Luckiesh-Moss Visibility Meter.

The relative visibility scale of the meter is calibrated in terms of the sizes of a series of standard parallel-bar tests-objects illuminated with 10 footcandles and viewed by an observer with average normal vision. In effect it is a transfer medium by which different visual tasks can be rated in terms of the visibility-levels of the standard series of objects. Units of measurement, of necessity, are defined by arbitrary standards that are relatively simple and readily reproduced. This scale of relative visibility has been applied effectively in the study of the visibility-levels of many diversified tasks.