Tactile Colour Contrast
TACTILE INDICATORS MUST PROVIDE A HIGH VISUAL CONTRAST TO THE WALKING SURFACE.
The colour or visual contrast between the walking surface and surrounding environment is technically know as the Luminance Contrast and is critical for people who have low vision. They are using their limited residual vision for orientation, distinguishing the limits of the footpath, recognising hazards and gathering information. Contrast is especially important in the provision of Tactile Indicators to warn pedestrians of hazards.
AS/NZS 1428.4 requires the following luminance contrast to the immediately adjoining surface:
1) For Tactile Pavers or Tiles of uniform colour (Integrated Tactile Indicators) 30%
2) For individual Tactiles of uniform colour (Discreet Tactile Indicators) 45%
3) For Tactiles with a different colour on the side than the top surface (Composite Tactile Indicators) 60%
Research by Bentzen et al (Accessible Design for the Blind - May 2000) indicated that the colour “safety yellow” is so salient, even to persons having very low vision, that it is highly visible even when used in association with adjoining surfaces having a Light Reflectance Value (LRV) differing by as little as 40%. Their research found that safety yellow TGSI having a 40% contrast from new concrete was subjectively judged to be more detectable than a darker TGSI having an 86% contrast with new concrete.
Visual contrast exists in three dimensions – Brightness, Hue and Saturation.
Brightness refers to the amount of light reflected by a surface – perceived as light or dark. Differences in brightness provide the main contrast available to a person with poor colour discrimination. It could be considered as the contrast that would be provided if the surfaces were viewed in black and white. Brightness is easily measured using a luminance meter. Minimum luminance contrast values are specified in Section 2.2 of AS/NZS 1428.4.1: 2009 which also details techniques for laboratory and on-site measurement of differences in Light Reflectance Value or luminance contrast.
Hue refers to the basic colour reflected by the surface, and can simply be described by the elementary colour names such as red, green, yellow, blue. It is most easily understood by reference to the colour wheels used in paint charts (see below). The greatest contrast is provided by colours on opposite sides of the colour wheel. Avoid using the same or adjacent parts of the colour wheel. If the aesthetics of the design dictate that TGSIs are to be of similar hue to the adjoining footpath surface, then an increase in the contrast should be sought by greater differences in brightness and saturation.
Saturation refers to the purity of colour. Highly saturated colours are pure and vivid. Colours with low saturation are pastel or dull. Red and pink may have the same hue but pink is less saturated. White and black have no saturation.
Some examples of effective and non-effective luminance contrast.
Luminance Contrast Calculator Tool.
If on a mobile device tap the blue field boxes twice to enter your LRV number.