In addition to the gradual shift of LEDs towards the red end of the spectrum, other colour changes can occur over the life of LEDs, especially if manufacturing defects are present. Two common such defects are Curling and Lamination.
LEDs work by producing blue light which is changed to white light as it passes through a layer of phosphors. The phosphors are usually visible as a yellow-coloured dot at the centre of each LED.
To check for peeling or lamination, remove the diffuser (if there is one) from the LED fitting in question and direct the beam of light directly at a mat-white painted surface. Especially on fittings with only a few LEDs, or where the LEDs are in a single strip, peeling and lamination will be apparent in the form of a blue or yellow “halo” visible around the edge of the light beam where it strikes the surface.
*The diagram above shows that the centre of an LED is the phosphor layer that transforms the blue light to white light.
In a correctly assembled LED, all the blue light passes through the phosphor layer and is transformed to a consistent quality of white.
CURLING occurs when the phosphor layer starts to peel at the edges, allowing some of the blue light to escape without being transformed to white.
LAMINATION occurs when cavities appear under the phosphor layer. These have the effect of increasing the distance the light travels through the phosphor layer, so the light becomes more yellow than originally intended.