Visibility Prediction Software: Five Factors of Contrast Perception for People with Vision Impairment in the Real World

Abstract

The use of colour contrast in the built environment for people with low vision has been largely unsupported for architects, access consultants or designers, with little information available and no easy-to-use tools. Accessible environments assist everyone including vision impaired people (VIP); yet often people can be disabled by buildings, not directly by their impairment (Pullin, 2009); in 2002 a total of 0.6% of the world’s population were listed as blind (Harle and McLannahan, 2008). A recent critique of accessibility recommendations showed a lack of understanding of the five key factors we identified for predicting an object’s visibility (Dalke, 2011) namely, visual ability (VA) of the observer, contrast, lux level, dimension of the object and distance away from the observer. These were established as fundamental for the perception of objects, texts or elements for VIPs, contrast being one of those five interdependent variables (Dalke et al., 2010); they are fundamental to the software that has now been developed to predict object visibility. The research carried out revealed gaps in how to achieve contrast practically for the professionals who should be more familiar with the process. In the USA, the ADA Standard for Accessible Design makes reference to contrast but it is ambiguous and open to interpretation. In the 1991 standard, 70 points of contrast difference are prescribed for marking warnings on walkways (ADA, 1991). But how to gauge contrast, by calculating the difference between the light reflectance values (LRV) of two surfaces, is always missing. In the UK there is no advice on how to check and deliver on contrast for accessible buildings and products (DDA, 2004; EHRC, 2010).