The role of colour and brightness contrast is integral to how people negotiate and understand the built environment.
Colour contrast is the degree of difference between one colour and another on the colour wheel: the more visually different the colours, the greater the contrast.
Brightness contrast (also known as luminance contrast) is the difference in brightness between one object or surface and another: the greater the difference in brightness levels, the greater the contrast.
A person with excellent vision could enter a well-designed and logically organized building with good signage, little or no glare and minimum shadowing and still experience a sense of disorientation if there’s little contrast in the colour or brightness of their surroundings. These problems increase significantly for a person with blindness.
In the built environment, colour and brightness contrast can be used effectively for many purposes. It can be used to identify a door opening, to draw attention to signage and to define a route of travel. It can also be used for orientation. For example, a building designer may opt to use different colours for different sections or floors in a building. However, consistency and simplicity are also important. Providing colour and brightness contrast at every turn or change in architectural detail can be confusing.
To benefit someone with blindness, all parts of a built environment must be considered when it comes to colour and brightness contrast. For example, a light-coloured door against a light-coloured wall would be easier to identify if the door frame and door were a dark colour, such as brown. A sign is much easier to locate when its colour and brightness contrast to the surrounding wall surface.
Wherever possible, the colour and brightness contrast of key elements in the built environment should be at least 50 per cent (higher levels are preferred). The colour and brightness contrast on signs and pictograms should be at least 70 per cent.
Use a light meter to measure the colour and brightness contrast of surfaces. Hold the light meter 200 – 250 mm above the brighter surface (B1) to measure its light reflectance value (LRV). Then do the same with the darker surface (B2). Plug your measures into this formula:
Section 4 of CSA/ASC B651:23 Accessible Design for the Built Environment
provides additional details on other means by which to measure colour contrast.
Additional research would be extremely helpful to determine the effectivness of these standards as they apply to people living with sight loss. One such approach would be to utilize vision simulators to assess the colour contrast as it would be perceived by someone living with sight loss. Vision simulators can be found online.
Several years back, AIRA Technologies, an organization which provides virtual agent visual interpreter services published a mobile application which helps anyone interested to see how people living with sight loss perceive their environment. The mobile application is free to download from the Apple App store.
Manufacturers often provide LRVs on paint chips and other material samples. LRV calculators can also be found online.
Follow these guidelines to produce colour and brightness contrast for exterior spaces, interior spaces and signs:
- Use noticeably different colours side by side to distinguish different key building elements. Some good combinations are:
- Chocolate brown/white
- Dark blue/white
- Dark red/white
- Dark purple/white
- Dark green/white
- Avoid these colour combinations, which have poor contrast:
- Light blue/white
- Avoid these colour combinations, which have poor contrast and are particularly difficult for people with colour blindness:
- White lettering on a dark background is easier to read for people impacted by blindness than dark letters on a white background. Further information is provided in the Signage section.
- Keep colour schemes simple to avoid confusion in your design. Too many colours and busy patterns create confusion.
- Be consistent in the use of colours to convey specific information. For example, use one colour for all entrances to women’s washrooms in a building and a contrasting colour for all entrances to men’s washrooms.
- When it’s impossible to adjust the colour or contrast of an item, consider other options. For example, when the colours in a corporate logo can’t be changed and the logo includes colours with poor contrast, place a contrasting border around logo signage.