The Objective of Luminance Contrast
Luminance contrast is important for everyone. A contrast in the Light Reflectance Value (or Luminous Reflectance Value) helps objects stand out, which could be a grabrail on the wall, a toilet in the corner of the room, or a sign on the wall. Providing a high contrast makes things easier to locate.
The Need for Luminance Contrast
This is especially important when you consider Vision Australia has estimated that there are currently 357,000 people in Australia who are blind or have low vision. Vision Australia has also projected that the number of Australians who are blind or have low vision will grow to 564,000 by 2030.
Ease of Navigation
Providing an LRV difference (also known as the ‘luminance contrast’) between surfaces also helps people navigate a building environment. A corridor with a high LRV difference between the floor, skirting boards and walls will aid wayfinding and help people clearly identify the path of travel.
Luminance contrasting bands around doorways help people identify the door and safely move through it. A glazing visual indicator band across glass doors aids in recognising that there is glass in the opening and attempts to warn people of the hazard so they don’t walk through the glass (see this article on Richard Branson’s accident),
Surfaces that differ sufficiently in LRV can be distinguished from one another by blind and partially sighted people. For people with good vision, differences in hue (or the nature of the colour) or chroma (the intensity of the colour) provide adequate visual contrast.
But this is not the case for people who are blind (with some level of sign remaining) or for those people with low vision. The main feature of a surface, which is strongly correlated with the ability to identify differences in colour, is the amount of light the surface reflects, or its light reflectance value (LRV).
The luminance contrast must, therefore, be higher for smaller surfaces, such as light switches, or lift buttons, than for larger flat surfaces such as walls and walls.
Lighting Considerations
Managing an LRV difference inside a building is much easier to control, with good lighting, compared to an external environment exposed to the elements (i.e. rain, frost, sun fading etc.) and natural lighting (i.e. darkness, glare etc.). Therefore, the positioning of signage, switches, controls and other features must carefully consider the available lighting.