Colour Temperature refers to an ideal black body radiator. Correlated Colour Temperature refers to a light source whose perceived colour most closely resembles that of a black body radiator. Correlated Colour Temperature (CTT) describes if the appearance of white light is warm (reddish), neutral or cool (bluish). It is expressed in Kelvin (K). Higher values relate to cooler colours.

LED’s do not emit pure white light. True white light has an equal intensity at every wavelength. If any wavelength has a higher intensity than the rest, the light takes on a hue related to the dominant wavelength.

Normal production LED’s will vary in colour, luminous flux, and forward voltage. Since the differences can be large, LED’s are split into subclasses or bins. Binning makes it possible to select LED’s that conform to stated specifications.

Lamp manufacturers choosing quality LED’s from a small selection of bins will minimize possible variations in the LED colour.

Manufacturers of cheaper LED lamps often select LED’s from a diverse bin range in order to keep costs as low as possible. This leads to the risk of LED’s within the same lamp having large possible colour variations.