As stated, LEDs are current devices, not Voltage. As long as you have Vf or Vf+ and stay below Imax, you get a light. The amount of time it takes to kill a LED is proportional to the amount of current you feed it at any voltage above Vf. It is actually the heat generated by passing current (yeah, I know, bad english, but the theory is correct). The more current, the more heat. The longer you apply the current, the longer it takes to disapate the heat, and, the more damage is donr to the junction area and the bond wires. If you burn an LED at high brightness for a long time and another at half brightness (think current levels), which one do you think will die first?
I have used red LEDs with MegOhm+ series current limiters as pilot lights in 110Vac circuits (more for continuity checking than pilots, but you get the picture. Voltage isn't really the issue.
Have fun.