tint shift as nichia led's "break in"?

[snakebite]

i bought a large quantity of nichia 3mm diffused white leds.
the guy i got them from was dissapointed in the tint for his project.
they were slightly purplish.
they are fine in ham radio displays and dc nightlights.
i put 3 in series across the switch of a ott light i converted to 12v by installing a thinlite ballast.
these led's have several thousand hours on them.they are on whenever the lamp is off/closed.
i did another for a friend who has solar.
same bag of led's that i opened myself.
same current on these too.
the unused leds are slightly purple but the ones with the runtime now are white!
they look neutral next to a 12v desk lamp with a thinlite ballast and "950" phosphor "full spectrum" tubes.
the new ones look purplish in this test too.

 

[JohnR66]

I can't see your photo, but I assume your viewing the difference at the same current that they were driven at when purplelish? Has overall output dropped?

I have not tested Nichia's, but LEDs I've tested would do the opposite (white to puplelish shift) or just lose some light output. It is possible the epoxy over the die has yellowed a bit causing the light to appear more white. That is the only logical explaination I can come up with.

Regardless of max current rating (20 - 30ma) I recommend driving these small 5mm and 3mm white LEDs at no more than 10 to 15ma where the LEDs are used in applications where they are expected to last for a few thousand hours.

 

[snakebite]

these are running around 10ma.
brightness is identical.
just the tint shift.

 

[JohnR66]

You may have something there.

I just checked my Radio Shack 276-0017 LEDs. These are neither warm white or cool white. They are around 4000 Kelvin 5mm LEDs. I have a couple running for 500 hours at 15ma. compared to several unused ones (I have about 30 of them!) they have a slight warmshift that is only apparent in side by side tests. They have not dropped in brightness. Believe it or not, they seem very slightly brighter than the others.

I cannot confirm any of this because I did not compare them prior to testing but I will step out on a limb and say that the operation time has affected them in some way because they are pretty consistant from LED to LED.

Given the good brightness and lumen maintenance of these LEDs, they are a high quality and perhaps even a Nichia product.