Expert in Optical & Thermal Measurement Solutions
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 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%.
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%).
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.
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.
They are the same in physical meaning: all of them are quantities representing the fraction of visible light reflected by a surface.
For general applications, the results are equivalent. For example: 0.50 (50%) of daylight reflectance = 0.50 (50%) of visible light reflectance = 0.50 (50%) of luminous reflectance = 50 of light reflectance value (LRV).
In practice, there are some subtle differences in the test results, due to the different test methods used. Below are the practices implemented in our lab:
Most of the time, the results obtained with different methods are very close (typically less than ±0.01 of variation).