Legibility Threshold Contrast of Uppercase Text Seen against a Dark Background

Abstract

A laboratory experiment was conducted to determine the effects of letter height, letter width-to-height ratio, stroke width-to-height ratio, inter-character spacing-to-height ratio, on the legibility of uppercase single words displayed in an achromatic, positive contrast polarity. Legibility was investigated in terms of threshold contrast. A total of 10 young, healthy subjects participated in the experiment which was conducted under carefully controlled conditions in a dark tunnel. A substantial amount of legibility optimization research on individual typographical parameters is found in the technical literature. However, no studies were located that simultaneously investigated the letter-height, the width/height ratio, the stroke-width/height ratio, and the spacing/height ratio in a full factorial experiment such as the one presented in this paper. The presented data can be used to optimize the legibility of uppercase, single words made up by the standard highway alphabet subject to sign size constraints.

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