metal halide bulbs and there life time frame

[mnewby]

how long can they run for is there A certin time they can run for before they can cause issues like i know some bulb after they peak can inhance bad alarge to grow ?

 

[lizardarm]

I don't think that there is a set answer that will apply to every bulb out there. The consensus seems to be that it's a good idea to change the MH lamps out about every nine to twelve months. As the lamps age their color temp will tend to shift; this shift could be towards the cooler (yellow) spectrum which may enhance algae growth. You get what you pay for with halides (not to say that the most expensive lamps are always the best), so be cautious of the dirt cheap lamps on ebay and such.

 

[dnjan]

That is (unfortunately) one of the reef myths. The colour shift is apparent, because the intensities of the bluer frequencies descrease more rapidly than the intensities of the yellow and red frequencies. However, NO INTENSITIES AT ANY WAVELENGTHS INCREASE. Therefore there will not be enhanced algae growth. The appearance (to the human eye) will, however, be less desirable.

Effective lamp life depends a lot upon the frequency range of the bulb. Bulbs with higher apparent colour temperatures (for example, 20k bulbs) will need to be replaced more often in order to maintain tank appearance than bulbs with lower apparent colour temperatures (6.5k bulbs).