Recognition time for dial type numerals as a function of size and brightness.

Abstract

Abstract : Recognition time as a function of digit size and brightness was determined for white dial type digits on a dark ground. The brightness range was from 0.003 to 0.1 foot-lambert. Average recognition time under the most favorable conditions tried was about 0.6 second. As size or brightness decreased, recognition time increased, at first slowly and then more rapidly. The effect of such secondary factors as individual differences, grouping of digits, and reduction in brightness contrast was relatively small when size-brightness conditions were favorable, but tended to be much larger when size-brightness conditions became difficult. So far as the variables here investigated are concerned, it would be desirable to maintain operational conditions such that single digits would be recognized by the median subject within about 0.7 second. The necessary size-brightness combinations, however, would involve complications with space limitations and dark adaptation, so practical compromises are necessary.