Rachapoom Punsongserm Researchers have developed the Thai universal design typeface (Thai UD typeface) to create more legible Thai letterforms. Previous studies have used various psychological methodologies to determine the effectiveness of legibility in the Thai UD typeface. One recent study used the multi-viewing distance threshold to measure the performance in legibility of three different typefaces, including FT Manifest UD (Thai UD typeface) and two familiar typefaces (e.g., Cordia New and TH Sarabun New), when presented with 36 Thai consonants at 15 varying viewing distances. The results showed that the FT Manifest UD typeface was superior in overall effectiveness compared to the Cordia New and TH Sarabun New typefaces.
The present study aimed to further investigate the capabilities of the Thai UD typeface by comparing it to Roman-like Thai typefaces (e.g., DB Ozone and Sukhumvit Tadmai) using the same methodology of the distance threshold. The experiment presented 36 Thai consonants at 15 varying viewing distances to 31 Thai volunteers, categorized into three groups: adolescent-young adults, older adults, and individuals working in graphic design and related fields. Our findings showed that the FT Manifest UD typeface was superior in overall effectiveness compared to the DB Ozone and Sukhumvit Tadmai typefaces, based on the Wilcoxon Signed Ranks Test, at a significance level of 0.05. This finding was consistent across all three groups.
The Thai UD font, also known as FT Manifest UD, was specifically designed to assist individuals with low visual acuity. However, our research found that its unique letter features also improve legibility for others under different visual angles and viewing distances. Our study suggests that FT Manifest UD is more effective than other typefaces regarding various visual angles and distances. However, our research also shows that some letterforms need improvement to ensure legibility under varying visual angles and distances.