How to Light

How to Light: Do white LEDs change colour over time?

This question has been answered by Thomas Holgeth, joint managing director of High Technology Lighting.

Most light sources will degrade over time and the LED is no exception. The electrical and thermal stresses on the components will have an effect on the colour performance eventually.

Most manufacturers only provide colour performance data on a fixture that is fresh out of the box. The problem that the LED brings is its extraordinary long life. We’re used to seeing life expectation figures, based on the light output of the LED module falling to 70 percent (L70) or 90 percent (L90). What we’re not used to seeing is any corresponding shift in colour performance.

The reported Macadam Ellipse performance at zero hours will change over time , so it is worth checking with the manufacturer if that data isn’t immediately available from the data sheet. This is particularly important in installations where good colour performance over time is essential, such as in art galleries and areas requiring good colour inspection. This also includes healthcare facilities where accurate assessment of skin tones is so important.

Remember that LEDs are just delightfully stupid semi-conductors developed to convert some of the energy passing through it to a light wave length defined by a mix of very rare RGB phosphors.

Power supply and thermal management criteria all must be correct to ensure that the MacAdam Ellipses and lumen power that you require are still the same MacAdam ellipses and lumen power you end up with. Maintaining quality of light and colour performance over time is a technical art that a lot of very clever people still struggle with.