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Re: Metal Halide/ Mercury Vapour Lights

MattJasper at aol_com wrote:

> Does anyone know how Metal Halide/ MV lights work? Exactly?
> Are they similar in design to flourescent lights? ie, the ballast is there 
> primarily to limit the current flowing thru the bulb, and they have a starter 
> unit to generate an initial electron flow thru the gas which then disconnects 
> once the lamp is ignited?
> I have seen warnings printed on MH luminaires, "Warning: 4500Volts". I'm 
> guessing this may be the operating voltage but 4.5 kV seems a little 
> excessive for a tube that's about 10cm by 0.7cm. What's inside them? What 
> metal, and which halogen? 
> Are MV lights more or less similar to MH lights? I have seen both these types 
> in operation and can see no difference in their discernible light colour. How 
> do they operate?
> Is there a website that anyone knows of where I can find this info?
> Thanks very much,
> Matt.

I cannot tell you much about how they work. I know that MV lights are way
less efficient than MH. In terms of the light available for photosynthesis
(PAR), they are only about 1/3 as efficient as a good MH, and less than
twice as efficient as an incandescent/halogen bulb. MVs also have too low
CRI ratings: usually in the range 20-25 for the high color temp types
(6000-7000 K), or 40-45 for low temp models (2000-3000 K). Hardly what we
strive for in a planted aquarium.

- Ivo Busko
  Baltimore, MD