Readability of a Horizontally Scrolling Text LED Sign Panel

- Effects of Viewing Distance, Scrolling Speed, and the Number of Phrases -

Abstract

The main aim of this study is to investigate the readability of a horizontally scrolling text LED sign panel placed above the passenger door of a train in Japan and to investigate the validity of non-subjective indices to evaluate its readability. An experiment to study the same was conducted on six subjects. The total width of the LED sign panel was 51.2 cm, and it could display up to eight Japanese characters simultaneously. Each of the characters consisted of 16×16 dots, and the color of the dots when lit was orange. In the experiment, each of the subjects equipped with an eye-mark recorder was asked to read Japanese sentences displayed on the scrolling text LED sign panel aloud and to evaluate subjective scrolling speed and readability of each sentence. These sentences were nonsense but grammatically correct. The experiments were repeated by varying viewing distance, actual scrolling speed, and the number of phrases. Findings are summarized as follows: 1）A difference between 72.1 cm and 254.4 cm in viewing distance had little effects on indices including the subjective readability. A difference of three and five in the number of phrases affected the subjective readability index, and the latter was evaluated to be lower. 2）The subjective speed index increased linearly while the scrolling speed was increased from two characters per second to eight characters per second. In contrast, the subjective readability index decreased significantly at eight characters per second. It was implied that these indices were also affected by the width or viewing angle of each character. 3）The temporal percentage of the gazes directed to the right half of the LED sign panel decreased linearly as the scrolling speed was increased. The percentage tended to be lower when the reading was incorrect.