LED Basic Parameters

Light Output

LEDs provide much higher light output on the same input power as comparable incandescent or fluorescent sources, because of their high efficiencies. This is also because the light emitted from the LED is naturally directional, and in almost all applications less light is lost in the fixture compared to traditional light sources. Colour quality is a key challenge facing LEDs as a light source for general lighting.

 Various light sources versus LED, part 1:

Part 2:

 Correlated Colour Temperature (CCT)

CCT describes the relative colour appearance of a white light source, indicating whether it appears more yellow/gold or bluer, in terms of the range of available shades of white.

The most efficient (up to 140 lm/W) high-output white LEDs are phosphor-converted devices based on blue LEDs, characterized by very high CCTs of 5000K or above. Warm white (from 2700K to 4000K) devices are now available at efficacies comparable with FLs (up to 120 lm/W).

Color Rendering Index (CRI)CRI is a measure of the ability of a light source to render colors, relative to a reference light source (incandescent bulb). CRI may be compared only for light sources of equal CCTs.