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The spectral G-Index is a variable that was developed to quantify the amount of short wavelength light in a visible light source. The smaller the G-index, the more blue, violet, or ultraviolet light a lamp emits.

Definition

The G-index is defined as follows:

$G=-2.5\mathrm {log} _{10}{\frac {\sum \limits _{\lambda =380\mathrm {nm} }^{500\mathrm {nm} }E(\lambda )}{\sum \limits _{\lambda =380\mathrm {nm} }^{780\mathrm {nm} }E(\lambda )V(\lambda )}}$

where

• G is the spectral G-index;
• λ is the wavelength in nanometers;
• E is the spectral power distribution of the lamp;
• V(λ) is the luminosity function

The sum is defined to be taken with a resolution of 1 nm.