luminance contrast

Preparing samples for luminance contrast test

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Related services Luminance contrast

The luminance contrast test is always in terms of two samples in a pair, typically one bright color sample and one dark color sample. There are two scenarios for sample preparation:

  • Side-by-side flat surfaces
  • TGSI studs on a flat surface

Side-by-side flat surfaces

For side-by-side flat surfaces, two flat-panel samples need to be submitted. Shown below is an example:

The preferred sample size is 100 mm x 100 mm or slightly smaller. The maximum sample size is 300 mm x 300 mm. Only 1 pair of samples (2 pieces) are needed and it is optional to provide additional samples as the backup.

TGSI studs on a flat surface

For Tactile Ground Surface Indicator (TGSI) studs on a flat surface, it is possible to submit the samples as either integrated samples or loose samples.

Integrated samples

Shown below is an example of an integrated sample of TGSI studs on a flat surface:

The preferred sample size of the integrated sample is 100 mm x 100 mm or slightly smaller. The maximum size is 300 mm x 300 mm. Only 1 sample is needed and it is optional to provide additional samples as the backup.

Loose samples

It is possible to submit TGSI studs and flat surface samples separately, without fixing them. Shown below is an example.

It is recommended to provide 2 – 5 loose TSGI stud samples.

For the flat surface sample, the preferred sample size is 100 mm x 100 mm or slightly smaller. The maximum size is 300 mm x 300 mm. Only 1 sample is needed and it is optional to provide additional samples as the backup.

Online luminance contrast calculator V1.0.0

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Related services Luminance contrast

We are pleased to introduce our online luminance contrast calculator (V1.0.0, first version). Click the screenshot below to access this online calculator.

The calculation principle of this calculator is similar to the online total daylight calculator. The luminous reflectances of the two sRGB colors selected are calculated with color space conversion. The luminance contrast is then calculated from the two luminous reflectance results.

Luminance contrast: calculation method and a few examples

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Related services Luminance contrast

Calculation of luminance contrast

Luminance contrast is a measure of the difference in brightness of two surfaces. People with vision impairment prefer higher luminance contrast to identify TGSIs (tactile ground surface indicators).

The surface brightness is measured by its luminous reflectance. The luminous reflectance of a surface is the fraction of visible light reflected by the surface and it is equivalent to the daylight reflectance, visible light reflectance or light reflectance value of the surface.

In our lab, the luminance contrast between 2 surfaces is calculated according to AS 1428.1:2009 or AS/NZS 1428.4.1:2009, with the following equation:

Luminance contrast = 125 x (luminous reflectance 1 – luminous reflectance 2) / (luminous reflectance 1 + luminous reflectance 2 + 25)

For example, the luminous reflectance of surface 1 is 50% (luminous reflectance 1 = 50); the luminous reflectance of surface 2 is 25% (luminous reflectance 2 = 25); the luminance contrast between them can be calculated as:

Luminance contrast = 125 x (50 – 25) / (50 + 25 + 25) = 125 x 25 / 100 = 31.25

The luminance contrast is therefore 31.25 or 31.25%.

A few examples of luminance contrast

Left: luminous reflectance = 63%; Right: luminous reflectance = 9%;
Luminance contrast = 69%

In the example above, the surface on the left (pale grey color) is significantly brighter than the surface on the right (deep grey color). The luminance contrast between them is large (69%).

Left: luminance reflectance = 27.4%; Right: luminance reflectance = 27.9%;
Luminance contrast = 0.7%

In the example above, the surface on the right is only marginally brighter than the one on the left. The luminance contrast between them is small (only 0.7%). When such a surface pair is used as TGSIs, it will be very hard for people with vision impairment to identify them.

Left: luminance reflectance = 23%; Right: luminance reflectance = 24%;
Luminance contrast = 1%

In the example above, the surface on the right (cyan color) is only slightly brighter than the one on the left (green color), the luminance contrast between them is small (only 1%), although they are quite distinct in color. Luminance contrast is different from color contrast. TGSIs with large color contrast but small luminance contrast are still not friendly to visually impaired people.