LED changes color?

i tried doing a runtime test on an inova knockoff running on 2x e² 123's. after about 12 hours i notice that 4 of the LEDs start to shine a light green color, while 1 of the LED still remains white. does anyone know why this is?

The white one has a higher Vf than the others, and the others are being overdriven and are shifting color because of heat/high current levels. The other ones probably won't last long. White leds turn a blueish green and dim down when they are being pushed closed to blowing up...

what do u mean by "higher vf"?

The term "Vf" means forward voltage. That is, the amount of voltage the LED needs in order to draw a certain amount of current - 20 milliamps is a very typical value you'd see with most round 5mm LEDs.

With a higher Vf, the LED would draw less current than the other LEDs in the same group using the same power supply. And while the other LEDs in the group may be being overdriven to the point of degrading and changing color, the one with the higher Vf would be receiving less current, and would be less likely to degrade in that manner.