LED response time (time to warm up)
The difference is, light emission from incandescent and fluorescent light bulbs is a secondary effect, light emission from LED's is a primary effect.

Obviously incandescent bulbs the light is caused by the heating of the filament to white hot temperatures. Fluorescent bulbs you are exciting a gas and the phosphor inside the tube to generate light.

In LEDs light is emitted directly from the semiconductor by quantum effects in the material itself in direct relation to the applied current. As holes and electrons combine the electrons transition between valance layers in the atoms. This directly releases photons of light.



As such, LEDs themselves, have virtually zero "warm up" time. Their turn off time is likewise short.

Having said that, many retail LED lamps and lamp drivers have a significant start delay. This is however, not due to the LEDs, but rather is part of the design of the driver.