On the standardization of VDT's proper and optimal contrast range

There are interactions in the effects of VDT luminance contrast and screen luminance on the operator's visual performance. The range of both optimal and proper contrast is the function of the level of background luminance on the screen. Increasing screen luminance results in a shift from optimal and proper contrast towards low contrast. The subjective evaluation method has the same validity as the performance index in assessing VDT display quality.