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Legibility Guidelines

Research conducted by Canadian National Institute for the Blind (CNIB) found that 'multiple variables can affect the reading performance of individuals with low vision.'

Certainly, the size and type of fonts used in large print materials are some of the most important considerations, however, after assessing the research included in this review, it is clear that other factors can play a role in determining the best conditions for legibility.

The presence or absence of serifs, contrast of text to page, thickness of letters, inter-letter spacing, leading, and the medium on which text is printed ...., can all affect the legibility of type. In addition, the role of typeface legibility plays an important part with respect to specific eye conditions.

Individuals with age-related eye diseases were the most common type of participants within the research studies assessed in this review, and there were many studies conducted on the specific issues associated with reading and age-related macular degeneration ('Clear Print' - an evidence based review of research on typeface legibility for readers with low vision April 2006 CNIB)

The extensive research carried out by CNIB resulted in a published review which is available on their website: Canadian National Institute for the Blind

Vision Australia bases its guidelines for optimum legibility on the CNIB work mentioned above, the principles of Universal Design, the work of Lighthouse International and gathered knowledge from our own experience and blindness agencies nationally and internationally.

By following these guidelines, you will be making effective choices for legible communication that will work for most people, including some people with low vision.

Universal Design is an approach to the design of all products and environments to be as useable as possible by as many people as possible, regardless of age, ability or situation. Universal Design is a philosophy, not a set of rigid or hard and fast rules, and can be applied to all types of products and services.

The seven internationally recognised Universal Design principles can be summarised as follows:

• Equitable use seeks to maximise the usefulness of design for everyone, identical whenever possible and equivalent when not, so that it avoids segregating or stigmatising any users.
• Flexibility in use values design that accommodates a wide range of individual preferences and abilities.
• Simple and intuitive use seeks to create ease of understanding for users, regardless of their experience, knowledge and language.
• Perceptible information seeks to ensure that design allows information to be communicated effectively to the user, regardless of ambient conditions or the user's sensory abilities.
• Tolerance for error seeks to minimise hazards and the negative consequences of accidental or unintended actions.
• Low physical effort seeks to ensure that interaction with the environment can occur efficiently and comfortably and with minimal fatigue.
• Size and space for approach and use seeks to maximise approach, reach and manipulation capabilities of users irrespective of their size, posture and mobility

The basic aspects of the design which will impact on the general legibility of a standard print document are:

• Stock choice
• Font choice - typeface and print size
• Colour contrast
• Text layout
• Design layout

Stock choice

Stock should be of good quality and thick enough so that print does not show through on the reverse side of the page. It should also have a matt finish, as the glare from paper with a glossy finish can lessen legibility for many people who are older or who have partial sight.

Font choice - typeface and print size - large print

• A minimum of 12 point in a common sans serif typeface such as Univers, Arial or Helvetica is recommended.
• Avoid italic, simulated handwriting, ornate or condensed typefaces.
• Font style or typeface can also affect reading speed, but this may partly depend on individual preferences.
• Large print reading materials can be helpful for low vision conditions such as age-related macular degeneration, cataract, glaucoma, diabetic retinopathy and any other condition where reading print is difficult, especially when central vision is affected (Vision Rehabilitation Evidence-Based Review Project Team and CNIB Research Key Points Summary 2006)
• Large print, which is set out in 18 point, is not just a matter of adjusting print size. There are various layout and design issues to be considered and these are available from Vision Australia.

Colour contrast

• The contrast between the background and the text is a vital factor in legibility (Effective Colour Contrast, Lighthouse International). The higher the contrast, the more legible the text will be.
• The size and weight of the font type will also affect the contrast. Black text on a white background provides the best contrast, while black text on a pale yellow or pastel background will work well if the text is crisp.
• There is also evidence to show that white text on a sufficiently dark background provides good colour contrast and legibility. Different colours may be important for aesthetic or branding reasons and, as high contrasts are not as easy to achieve with colour combinations other than black and white, the contrast needs to be viewed with care.

A tool for checking foreground and background colour combinations on the web to determine if they provide good colour visibility is called the Colour Contrast Analyser which determines 'colour visibility' and is based on algorithms suggested by the World Wide Web Consortium (W3C) .

"Two colours are considered to provide good colour visibility if the brightness difference and the colour difference between the two colours are greater than a set range." The range suggested by the W3C is > 125 for colour brightness and > 500 for colour difference.

Note: Hewlett Packard (HP) provide an online colour contrast verification tool that uses the W3C algorithms, but sets the Colour Difference range at > 400, which results in a greater range of foreground & background colour combinations being deemed acceptable.

You may find the Colour Contrast Analyser verification tool useful for assessing colour contrast on Powerpoint presentations.

Text layout

Alignment

• Text should be left justified to retain legibility and neatness.
• Avoid indenting paragraphs as the left margin is used to orientate the reader.
• Full justification creates different spaces between words and can cause 'rivers of white'. For some people this makes it hard to follow the line of print.

Margins

• Where material is to be bound, then a wide binding margin is recommended, making it easier to hold the volume flat.
• People using visual aids such as a stand and video magnifiers will need it on a flat surface.

'Leading' and Spacing

• 'Leading', or spacing between the lines of text, should be at least 25 to 30 percent of the point size. This is because people with partial sight or some forms of learning disability have difficulty finding the beginning of the next line while reading.
• Allow for equal spacing between words and generous spacing between paragraphs.

'Crowding'

• 'Acuity for letter recognition is known to be worse when multiple letters are presented with narrow inter-letter spacing than with wide spacing' (Research results Lei Liu PhD and A Arditi PhD Optometry & Vision Science Vol 78 No 1 2001).
• It is recommended that letters be well spaced so that the words, in effect, 'pop out' on the page. This is especially necessary for people with central visual-field defects.

Distinctive and simple design

• The basic principles of good simple design apply when designing for maximum legibility.
• It is recommended that headings or other information which it is necessary to highlight be placed in a prominent position in bold font.
• Underlining or italics are not recommended.
• Careful use of pictures, icons and diagrams can make it easier to identify the key pieces of text and provides additional cues for meaning.
• The use of clearly displayed lists can assist, as can text boxes, separate from the body text. Information highlighted in text boxes should stand out with high contrast and large font size.
• Vision impairment often makes it difficult to find a brochure or flyer that is buried among similar publications. The use of distinctive colours, sizes and formats can be especially helpful to older individuals and those who have partial sight.

This page last updated: 08 December 2009

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