Glossary

Calculated Parameters on the WaveGo App:

Colour Rendering Index (CRI)

A quantitative measure of how a light source reveals the true colour of an object, compared to an ideal or natural light source.

CRI is calculated from the difference in chromaticity of eight standard colour samples when illuminated by both the light source to be tested and a reference light source with the same correlated colour temperature. The CRI value represents the similarity between the color sample under the measured light source and the reference case. The maximum CRI value of 100 indicates that the object appears identical to how it would under the ideal reference light source.

R1-R8

Difference in chromaticities from each of the 8 standard colour samples.

Ra

Average of R1-R8.

R9-R15

Difference in chromaticities from each of the 7 additional (more saturated) colour samples.

Correlated Colour Temperature (CCT)

The inverse of a conventional description of “warmth” of a light – high CCT is white/blue, low CCT is yellow/orange.

 

TM30

A quantitative measure of how much a light source affects the colour of an object, compared to an ideal or natural light source.

TM30 is a colour rendering measure, developed by the IES. It is calculated by comparing to 99 colour samples (rather than CRI’s 8). The colour samples are chosen to represent real world objects such as skin colour, plants, textiles etc.

Fidelity Index (Rf)

A measure of the chromaticity difference, averaged over 99 different colours. A value between 0 and 100 is possible.

Gamut Index (Rg)

A comparison of the chroma of a light source to that of daylight. A measure of the intensity/saturation of colours under a particular light source. A Rg value less than 100 indicates a decrease in saturation compared to sunlight. An Rg value more than 100 indicates an increase.

Lux (lx)

The brightness of a light as perceived by humans or the intensity of light reaching a surface as it would be perceived by humans. 1 lux = 1 lumen/square metre.

Equivalent Melanopic Lux (EML)

A qualitative measurement describing the biological effects of light on humans.

Photosynthetically Active Radiation (PAR)

A quantitative measure of the number of photons emitted every second within the PAR region (400nm to 700nm).

Spectral Power Distribution (SPD)

The shape of the spectrum measured from a light source. The power per unit area per unit wavelength of a light source.


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