The choice of font can affect the legibility of text both printed and on a screen. The character shape, text format and layout can enhance or detract from the intended meaning.
Types of fonts
Fonts refers to the appearance of a "family" of characters used for text. In addition to the upper and lower case version of each letter, it includes numbers, punctuation marks and symbols. There are several common font families:
Cursive fonts resemble hand-written pen or brush strokes, often have artistic ornamentation, and sometimes have strokes that connect the letters together. Because cursive fonts are generally more difficult to read, they are usually a poor choice in terms of usability or accessibility.
Fantasy fonts are primarily decorative, and are not designed to be used as the main font for long passages of text. Fantasy fonts vary considerably in their appearance and artistic content. There are no elements or particular characteristics that categorize fantasy fonts other than their decorativeness. Like cursive fonts, fantasy fonts are generally a poor choice in terms of readability.
Serif and sans serif fonts
These are the two most common categories of typeface: serif typefaces, which have little "feet" (serifs) at the ends of the letters and sans serif, which do not.
Although, according to the RNIB (2007) "there is no scientific evidence to suggest that one category is easier for people with sight problems to read than the other", in general, legibility is higher with simple 'open' typefaces.
In many sans serif typefaces the lower case is visually similar to the capital For instance, the meaning of is more difficult to read in Arial than in Tiresias font .
Increasingly password and email addresses use both letters and numbers. For such applications it is essential to use a typeface which clearly differentiates the numeral and lower case For example:
Numerals in fonts
When designing a font, the formation of numeral characters should be considered. For example, Arial is a poor typeface for numerals such as it is preferable to use more open numerals such as This example of some open characters shows how the ends of the strokes can appear to close upon the letter and make them less easy to distinguish. Legibility may be reduced further in a bold format as the characters become more 'closed' and the white space within them decreases.
In some applications where the context does not make the meaning obvious, it may be essential to be able to differentiate the zero and the capital ; in this case it may be necessary to use a cancelled zero
Recent research (Rubin et al, 2006) looked at the impact of type size on the ability of people with a sight problem, who are able to read print, to read fluently. The research indicated that a person's reading speed increases as the size of the text increased.
Letter spacing is also called tracking and refers to the amount of space between a group of letters to affect density in a line or block of text. The amount of letter spacing in text can affect legibility. Tight letter spacing, particularly in small text sizes can diminish legibility. Added white space around the characters allows the individual characters to emerge and be recognised more quickly.
Below are some common example of where appropriate character spacing is required:
- m and rn
- oa and oo
- cl and d
Kerning is a term applied specifically to the adjustment of spacing of two particular characters to correct visually uneven spacing.
In digital typography, kerning is usually applied as a number to be added to the default letter spacing, expressed in the font's coordinates system when it is designed.
Problems encountered by disabled people and the ageing population using fonts
Blind and Partially Sighted
The contrast and colour of text against its background can affect legibility; this can be a severe problem for people who are colour blind.
Many dyslexic people find that the readability of a piece of text varies greatly depending upon the font used. Serif fonts, with their "feet" at the end of most strokes can tend to obscure the shapes of letters.
According to Litterick (2006), many dyslexic people find it "easier to read a font that looks similar to hand writing as they are familiar with this style". However these types of fonts can lead to confusion with some letter combinations, such as "oa" and "oo"; "rn" and "m".
The size of the ascenders and descenders of letters is also important as many dyslexic readers rely on recalling the visual shape of a word. If ascenders and descenders are too short the shape of the word is more difficult to identify and can make reading slower and less accurate.
Due to loss of focus or more serious visual conditions elderly people can tend to find that more uniform fonts are more legible and usable, and that overly thick or thin stroke-widths, and overly condensed or expanded styles are not suitable.
- Characters have consistent stroke widths
- Characters have pronounced ascenders and descenders
- There are distinct forms for each character (such as tails on the lowercase letters “t” and “j”)
- There are extended horizontal strokes for certain characters (such as the arm of the lowercase letter “r” or the crossbar of the lowercase letter “t”)
- Clear print fonts have a minimum type size of 12 point
- There is clear letter spacing between each character
- Kerning between specific characters is sufficient so as to ensure legibility
- Avoid the use of italic fonts as they are more difficult and slower to read
- Avoid creating a font that has red text on a green background or yellow text on a blue background
- Avoid patterned backgrounds for fonts
- Ensure the font has both upper and lower case letters as it is easier to read text in upper and lower case than all capital letters
Examples of fonts designed for legibility
Tiresias family of fonts
In response to the need for a family of fonts designed for legibility Dr. John Gill at the RNIB Scientific Research Unit, designed and aided the development of a typeface family specifically for use with keypads, large print documents, PC screens, TV screens and signs and labels.
- Tiresias Keyfont
- Tiresias LPfont
- Tiresias PCfont
- Tiresias Screenfont
- Tiresias Signfont
The Tiresias™ family of fonts are now free to download.
The American Printing House for the Blind (APH) has developed a typeface known as APHont, which was specifically designed to be used by readers with vision problems. It incorporates: consistent stroke widths; an under-slung “j” and “q”; open counterforms and larger punctuation marks.
- The Americans with Disabilities Act (ADA) Part 36 - Nondiscrimination on the basis of disability by public accommodations and in commercial facilities :4.30.2 - sets down body-width to height and stroke-width to height ratios for the use of appropriate typefaces in signage systems.
- DIN 16507-2 (1999) Printing technology - Type sizes - Part 2: Digital typesetting and related techniques
- American Printing House for the Blind (2004) APHont: a font for low vision. [accessed 18/09/08].
- Fennell, A. (2006) Investigation into the legibility of Tiresias keyfont version 1 and the development of Tiresias keyfont version 2. [accessed 23/06/08].
- Gill, J. & Perera, S. (2003) The Tiresias family of fonts. [accessed 23/06/08].
- Perera, S. (n.d.) LP font: an investigation into the legibility of large print typefaces. [accessed 23/06/08].
- Wikipedia (2008) Typeface. [accessed 15/09/08].
- Wikipedia (2008) Typography. [accessed 15/09/08].
The information contained in this section was taken from the following sources:
- Arditi A. (1999) Making Text Legible: Designing for People with Partial Sight. [accessed 19/06/08].
- Litterick, I. (2006) Typefaces for dyslexia. [accessed 15/09/08].
- Microsoft (1999) Character design standards. [accessed 17/09/08].
- Nini, P. (2006) Typography and the aging eye: typeface legibility for older viewers with vision problems. [accessed 17/09/08].
- RNIB (2007) See it right: making information accessible for people with sight problems. Peterborough: RNIB.
- Rubin, G. S., Feely, M., Perera, S., Ekstrom, K. & Williamson, E. (2006) The effect of font and line width on reading speed. Ophthalmic and Physiological Optics, 26(6), 545-554.
- WebAIM (n.d.) Fonts. [accessed 15/09/08].
- Wikipedia (2008) Kerning. [accessed 15/09/08].
- Wikipedia (2008) Letter-spacing. [accessed 15/09/08].