This PhD thesis investigates the influence of typeface stroke width on reading performance for low vision adults. While scientific evidence suggests that an increased stroke width—or bolder typeface—can improve legibility, optimal values are not well understood. In keeping with this, existing accessible design guidelines in the United Kingdom recommend a large range of typeface weights from regular to bold. The goal of this PhD research is to inform print design guidelines with a higher degree of specificity, and thereby increase the proportion of the population able to access text.

This research is based upon an initial inquiry formulated around one main question: What is the optimal typeface stroke width for low vision adults? In order to address this question, an integration of knowledge drawing from vision science and typographic design is undertaken. The majority of research into typeface legibility exists within vision science, while the creation of typefaces and expertise in their use exists within the discipline of design. This PhD responds to the lack of interdisciplinary approaches to typeface legibility research, which has resulted in limited application of scientific research to design practice.

This practice-based communication design PhD addresses the research question through a quantitative analysis of text typefaces. This involves the measurement of typeface proportions and the analysis of this typeface data through information visualisation. Typeface data is initially gathered with the purpose of designing a typeface for experimental testing. It is through this typeface design practice that the methods for the quantitative analysis of typefaces emerge, which then become the focus of the research. This PhD investigation develops a foundation of interdisciplinary—science and design—typographic knowledge, based on typeface data.

This research consolidates scientific knowledge on the influence of boldness on legibility in the context of low vision. Ten scientific legibility studies are analysed. This entails measuring and visualising the stroke width values of typefaces that have been experimentally found to have higher and lower legibility.

Design knowledge is formalised by measuring and visualising the stroke width values of typefaces commonly used in design practice. This is a design phenomenology study as defined by Nigel Cross, investigating design knowledge residing in artefacts themselves. By integrating scientific and design knowledge as proposed, interdisciplinary knowledge on typeface legibility for low vision adults is developed. My original contribution to knowledge includes visualising how the stroke widths of typefaces experimentally found to improve legibility relate to the stroke widths of typefaces commonly employed in design practice.

This thesis concludes that typefaces with stroke width values ranging from 22-33% (percent of x-height) improve legibility in the context of low vision. The analysis further indicates that sans serif regular typefaces range from 13.5-19.8% stroke width and are not optimal for low vision reading. The analysis also indicates that sans serif bold typefaces range from 18.9-40.0% stroke width, and that many, but not all, may improve reading performance for adults with low vision. This research is intended to be useful for legibility researchers and the development of evidence-based accessible design guidelines.