Affiliations: [a] School of Optometry and Vision Science, University of New South Wales, Sydney, NSW, Australia
| [b] Faculty of the Built Environment, University of New South Wales, Sydney, NSW, Australia
| [c] Association of Consultants in Access Australia, Sydney, NSW, Australia
| [d] Current address: Faculty of Engineeering, Parahyangan Catholic University, Bandung, West Java, Indonesia
| [e] Current Address: Vision Science and Optometry, University of Canberra, Bruce, ACT, Australia
Correspondence:
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Address for correspondence: Stephen Dain, School of Optometry and Vision Science, University of New South Wales, Sydney, NSW, 2052, Australia. Tel.: +61 414 385 622; Fax: +61 293 138 602; E-mail: [email protected].
Abstract: BACKGROUND: Standards writers, national and international, have used different contrast calculations to set requirements in building elements for people with visual impairments. On the other hand, they have typically set a single requirement (30%) for specifying the minimum contrast. The systems are not linearly related and 30% means something rather different in each system. OBJECTIVE: To provide a comparison of the various scales in order to illustrate the differences caused by multiple scales with a single compliance value, recommend a single scale for universal adoption and, if a new measure is problematic for implementation, to recommend the most perceptually uniform of the present methods. METHODS: We use the contrast between combinations of 205 paint colours to illustrate the relationships between the measures. We use an internationally accepted scale, with equal perceptual steps, as a “gold standard” to identify the most perceptually uniform measurement scale in the existing methods. RESULTS: We show that Michelson contrast is the most perceptually uniform of the existing measurement scales. We show the contrasts in the proposed method that equate to the various current requirements. CONCLUSIONS: We propose that CIE Metric Lightness could be used as the contrast measure. Alternatively, Michelson contrast is the most perceptually linear of the current measurement scales.
