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Abstract
Effects of character size under ambient luminance and light source on legibility of electronic papers were studied. Legibility was evaluated by a letter-search task. The results showed that search speed increased with luminance level and character size. However, the effect of luminance and light source on search accuracy was not statistically significant.

1.Introduction
The Electronic papers have become an attractive topic in the new generation of visual displays due to the lightweight, low power consumption and sunlight readability. The expectations of an electronic paper have been summarized by Mopani as flexibility, readability, andmulti-functionality [1]. Several technologies, such as liquid crystal display, electrophoresis display, interferometric modulation, and rotating ball display, have been developed to realize the expectations. Among these technologies, electronic paper made of cholestericliquid crystal (Ch-LC) and electrophoresis electronic ink (E-ink) is likely the only available products in the market [2, 3]. Although they have been available in the market for a while, there is no serious evaluation for their legibility based on the ergonomic consideration. Early studies of ergonomic requirements on reflective liquid crystal displays simulated by printing image were investigated by Kubota [4]. He found the required contrast depends on the background lightness, and the older subjects required a higher lightness and contrast compared with the younger subjects when the Japanese character size was smaller than 15 point. The first study on commercial electronic paper was conducted by Isono'sgroup [5]. Their study of visual fatigue from reading electronic paper made of E-ink revealed that there was no significant difference in the level of visual fatigue between electronic reading and conventional reading. It is expected that legibility will depend on ambient illumination since the VDU uses the ambient light as its reading source. Therefore, we focused on the ambient illumination effect on legibility of electronic papers [6, 7].Our results showed that legibility depended on the illumination level but light source. Printing image on paper had the highest visual comfort rating than the electronic papers although they have similar rating in the objective letter-search task.

In this paper, we extended our studies to the effects of character size, ambient luminance and light source on legibility of two reflective-type bitable displays and compared them with paper. Character size is an important factor affecting visual legibility. The proper characterize for electronic paper deserves study. Legibility was evaluated by using the method of letter-search task. The method of letter-search task was found to be practical to evaluate the legibility of a display [8]. The ergonomic evaluation and comparison between commercial electronic papers and paper could reveal that whether the current specifications are good enough for reading.

References
[1] M. Mopani," What is Electronic Paper? The Expectations", in SID Dig., pp. 128-131, 2004.
[2] Kent Display, Inc., Kent, OH 44240, USA.
[3] E-ink Corporation, Cambridge, MA 02138, USA.
[4] S. Kubota, "Ergonomic Requirements for Reflective Liquid-Crystal Displays", Displays vol. 19, pp. 121-125, 1998.
[5] H. Isonomy, S. Takahashi, Y. Takiguchi and C. Yamada., "Measurement本论文由英语论文网提供整理，提供论文代写，英语论文代写，代写论文，代写英语论文，代写留学生论文，代写英文论文，留学生论文代写相关核心关键词搜索。