Luminance contrast: a slippery concept

The Technical Insights section of the Autumn 2023 edition of Access Insights is about luminance contrast. This is a hot topic of discussion because it is a slippery concept. What is it and how do you measure it are the starter questions, followed by why do we need it.

This image, courtesy the Egress Group, shows discrete silver tactiles against a dark red carpet. The light grey stair nosings are also contrasted against a black carpet.

Silver discrete tactile indicators on a red carpet on a stair landing showing good luminance contrast.

Howard Moutrie explains that luminance is the amount of light reflected from a surface. The contrast is the amount of light reflected from abutting surfaces. For example the wall and the floor. This is not the same as colour contrast. Red and green are stark contrasts but will often provide the same amount of luminance. Therefore there is not luminance contrast.

So how do you determine luminance contrast? This is where it becomes slippery. Are you measuring this in a laboratory under controlled conditions? Are you measuring it on the street on a rainy day? Or are you measuring it a nighttime? An appendix to the Australian Standard (AS 1428.4.1) is part of the standard with the most up to date calculation.

Moutrie goes on to explain how testing on tactile indicators is not the same as testing on other surfaces. Then there is the issue of how different instruments provide different measurements for the same thing.

The original requirement for a 30% contrast was based on an integrated tactile where the whole surface provided the contrast. Individual tactiles, such as individual stainless steel ones, are supposed to have 45% contrast. Moutrie is critical of the way luminance is measured but the industry has geared up to meet these measurements. He says more research is still needed.

Why do we need it?

People with low vision need the contrast to navigate the environment, including at home. It helps distinguish a door from a wall, and the wall from the floor. It’s also good for people with impaired visual perception. For example not being able to see a white toilet pan in an all white bathroom.

There is more on this topic in, Luminance contrast: how do you measure it? With the cost of measuring apparatus, much is left to doing by eye. Or relying on manufacturers claims.

The title of Moutrie’s article on page 22 is Luminance Contrast – is what you see, what you get?

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