Metal Halide Frequently Asked Questions
How much time will it take to restart a metal halide bulb after the power has been turned off?
Metal Halide bulbs need to cool before they can be restarted. Most metal halide ballasts will 7-15 minutes to restart.
In the event of a power outage, a magnetic ballast will continue to supply power to the bulb until it restarts whereas most electronic ballasts will enter a rest period for seven to ten minutes before attempting to restart the bulb.
Why does my metal halide bulb flicker and turn off?
New metal halide bulbs require up to 100 hours to burn in and could flicker or turn off during that "break in" period.
If your bulbs are not new and flicker or turn off then you need to check that you are using the correct ballast for your bulb.
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Can I overdrive a metal halide bulb?
With the exception of Radiums, no. Overdriving a metal halide bulb could possibly explode or damage both the ballast and bulb.
When you overdrive a bulb you are supplying more amperage to the bulb than it is designed to operate on.
Can I run a metal halide bulb on DC current?
No, most metal halide bulbs are meant to be operated on AC current only.
How many hours each day should I run my metal halide?
When operating your metal halide without any supplemental lighting it is suggested that you run them 12 hours per day.
When using supplemental lighting, such as VHO's or compact fluorescents, you can run the metal halides 8-10 hours per day in conjunction with 12 hours of supplemental lighting.
For instance, the supplemental lighting could turn on 2 hours before the metal halides and turn off 2 hours after the metal halides do to simulate a dawn/dusk effect.
Do metal halides need a UV shield?
The outer glass envelope of a single ended metal halide lamp filters out most of the UV rays emitted from the arc tub.
Double ended bulbs on the other hand do not have an outer glass envelope to filter UV, so it is necessary to use a tempered glass shield to filter the UV rays.
How many metal halides do I need for my aquarium?
The general rule of thumb for even light distributution is 1 bulb for every two feet of tank lengthwise.
Do I need to supplement my metal halide lighting with actinics?
Although it has been proven that light in the blue end of the spectrum is beneficial to corals, the decision for actinics usually comes down to aesthetics.
Bulbs in the 5500K - 6500K range are considered to be on the yellow side, and should be supplemented with actinics.
10,000K bulbs can stand alone but most aquarists will use actinic supplemental lighting.
Any bulb above 10,000K can most likely stand alone without needing the use of actinics.