Effectiveness of predominant letterforms in different small type sizes Thai universal design font versus familiar Thai text fonts

Earlier researchers have investigated and suggested how to design legibility for Thai letterforms that evolved into the Thai universal design typeface (Thai UD typeface), which supports Thai readers and visually impaired people. Prior researchers measured the letterforms of the Thai UD typeface for effectiveness on various psychological methodologies, such as blur simulation, short exposure, and distance threshold method. To continually investigate the effectiveness of the Thai UD typeface, in the present study, we tested its capability by adapting the methods involved in critical print size ( CPS), letter acuity (LA), and reading acuity (RA) compared to familiar text typefaces. In the current study, we compared the effectiveness of three typefaces: FT Manifest UD (Thai UD typeface), Cordia New, and TH Sarabu New, which employed 36 Thai consonants in 15 different type sizes of the three typefaces. We presented the Thai characters to 32 Thai volunteers, including 12 males and 20 females between 18 and 62 years old, and we also divided the volunteers into three groups: adolescent adults, older adults, and graphic designers and related fields, into three different results. The Wilcoxon Signed Ranks Test showed that at a significance level of 0.05, the FT Manifest UD typeface was different in overall effectiveness from (better than) the Cordia New and TH Sara bun new typefaces. For the finding of each group, the FT Manifest UD typeface was different in effectiveness from (better than) the Cordia New and TH Sara bun new typefaces among the adolescent-young adults and the older adults. The finding for the graphic designers' group revealed that the FT Manifest UD typeface differed in effectiveness from (was better than) the TH Sarabu New typeface. However, the effectiveness of FT Manifest UD was similar to the Cordia New typeface. The study suggests that the most critical characteristics of FT Manifest UD provided better effectiveness than the other typefaces on various small type sizes. However, certain letterforms should be improved to enhance sufficient legibility for using the types in small and diminutive.