1. How can I compare the quality of light from LEDs?

Quality of a light source is generally described as providing full spectrum light. Full spectrum light is color-corrected light that simulates the clear brilliance of white light and the optical beauty of outdoor light at noon. There are several specifications commonly published to provide information on the quality of the light emitted, CRI, GAI, and CCT.

Color Accuracy – CRI (Color Rendering Index) is the ability of a light source to reproduce the colors of objects accurately compared to an incandescent lamp, on a scale of 0-100, where 100 is the most similar.

A CRI of 85 to 100 indicates quality color rendering

Test: 25 colored panels are viewed under both the incandescent lamp and the light source being tested, the more similarly the colors look under each light the higher the CRI score.

It is now generally accepted that a CRI score of 99 may not be preferable over a CRI score of 90. New light sources like LEDs are better at rendering blues and greens than the incandescent light to which they are compared.

Gamut Vividness – GAI (Gamut Area Index) measures how vivid objects appear under the light. Low numbers denote a small range of color that can be differentiated under the light, high numbers denote a large range of color that can be differentiated.

A GAI score between 70 and 100 is generally perceived as the most realistic.

Daylight compared to Non-LED light sources

Daylight compared to LED light sources

Source: ASSIST Recommends: Light Source for Color Retail
Lighting; Mark Rhea PhD, Jean Paul Freyssinier MSc LC

Test: Various colors are viewed under the tested light source and a measurement is taken on how well one color can be distinguished from neighboring colors on the color chart.

Color Temperature – CCT (Correlated Color Temperature) measures, in degrees Kelvin(K), the range of colors within white light. A CCT of 3500K is neutral, meaning the reds and blues are balanced in the white light produced.

3200k and below are considered warm white; 4000k and above are considered cool white.

Test: The color spectrum of a light source is measured against the established scale for white light derived from heating a tungsten filament. At 2700K the filament glowed a reddish white light and at 4000K it glowed a bluish white light.

Each color temperature represents a line on the color scale rather than a point. As such, two LEDs of the same color temperature may not appear the same if they are at two different points on the same color temperature line.