an innovation by nucon.de

LEDs have a much longer life time than other light sources, when keeping their temperature and their current below certain limits. Reduction of brightness or a color shift is very small when LEDs are driven for maximum life time but it is there.

When having a look on an LED installation of cheap flood lights in a riders hall, where 50% of the devices are out of service after a few years  of operationial time only,  you can see that the remaining devices have a different color temperature to each other.

               

The white LEDs are blue LEDs having a yellow phosphor converter layer on it, which is changing its transmission and converting performance over the life time. There is always a slight blue shift followed by a yellow back shift. If in case there is lot of heat impact on LED devices the blue shift in the beginning is very small followed by a strong yellow shift.

If in case there is a strong yellow shift prersent and the life time is below the promissed operational time it is a strong indication, that the LEDs had been operated too hot.

The cause of color shift due to aging was reported by  Davis, Mills, Yaga, Johnson.

On car head lights a shift of the color temperature is a very unwanted behavior especially if you can nor replace LEDs of such reflectors to obtain a symmetrical again. There are cases reported that one side of the head light was replaced due to a crash and the rplaced head light does not match the color of the old one. Low beam and matric LED hign beam does not match anymore to each other , see the following link: low beam yellow high beam white!

If in case your LED head light shows a color shift to yellow and the involved unit does not offer a service of the installed LEDs insight such head lamp, the conclusion must be that the car manufacturer has to replace such a unit for free no matter if a warranty has already timed out or not since such system was designed and offered to last a car life time. Such head lights costs so much money in the case of a replacement, that a customer can expect, that it was designed to avoid color shifts. The question is, how this goal can be achieved if head light manufacturers design the life time of such head lights only to last 8000 hours. Is a too hot operation not already tolerated in such designs to provoke color shift of a number of LEDs?