Why do HMI lights fade after use?

Question: Why do HMI lights fade after use!?

They begin to lose kelvin after 500 hours!. Anyone know why!?Www@QuestionHome@Com

Best Answer - Chosen by Asker:

With age, the arc length becomes larger and larger as more of the electrodes burn away!. This results in more voltage being needed to sustain the arc, and as voltage increases, color temperature decreases proportionately at a rate of approximately 0!.5–1 kelvin for every hour burnt!. For this reason, and other safety reasons, HMI bulbs are not recommended to be used past half their lifetime!.Www@QuestionHome@Com

Unfortunately, HMI lamps do not last forever!. Eventually, the lamp/bulb will need replacing!. The main reason is probably due to the degradation of material, over time, in this case mercury-halide, or perhaps even it's balast!. The mercury is held as a vapor and mixed with halides struck with a medium arc set of tungsten coated electrodes, if any one of those components wears down, you'll have degradation of not only color temperature, but overall performance of the lamp itself!. 500 hours is a long time and probably approaches the life expectancy of the bulb anyway!. The average life span of a 4000 watt, 200V HMI lamp is 500 hours!. Be careful, HMI lamps tend to become unstable after their life span has been reached, they are prone to exploding!.Www@QuestionHome@Com