Accessibility and Visual Contrast: A Proposal for a Better Evaluation of This Physical Quantity

Abstract

In Europe CEN, CENELEC and ETSI have been working and are still working on a series of standards, according to the European Disability Strategy 2010-2020. ISO has many working groups working on accessibility, including the one charged with the revision of ISO 21542 on Accessibility and usability of the built environment. In this framework, a great attention is now being given to the definition of design considerations useful to facilitate orientation and to ensure safe use of an environment, particularly for people with visual impairments. The physical quantity more related with human visual perception is visual contrast, and several existing standards refer to this quantity to establish minimum values to be provided to aid perception of information, building elements, etc. In this work, the authors face the problem of identifying which parameter may be most suitable to describe visual contrast, according to human sensation. The discussion focuses on the alternative between the use of the LRV (Light Reflectance Value) and the CIE Y tristimulus value, but also on the right formula to adopt to quantify the visual contrast between two adjacent surfaces. In order to contribute to an improvement of international standards now under development, the authors examine several guidelines, standards and recommendations, comparing the different evaluation methods and requirements adopted and finally give their suggestions.