They are based on recommendations from the Royal National Institute for the Blind , The Lighthouse Inc , other research and, where there is no better guide, our own taste and prejudice. The choice of typeface is less important than contrast, type size, weight and the spacing of characters. Quirky, unusual, script and titling faces are obviously highly inappropriate for legible continuous text.
Seriffed faces are more 'readable' in continuous text for regular reading.
This may equally apply to large print texts. Helvetica bold' was adopted widely as the result of some testing carried out in the 1970s. Now we have the results of more recent investigations alongside a much wider range of typefaces to choose from. We suggest avoiding very light-appearing weights of fonts. Sometimes 16pt may be needed by some visually impaired readers.