# Mercury Vapor???



## QuantumCranker (Oct 9, 2005)

I was wondering....what is the difference in mercury vapor and metal halide? I mean why do you never hear of anyone using the "streetlight" type 175 watt MV fixtures in a DIY lighting setup? (not the ugly orange municipal type but the whitish-blue backyard security light variety) They are much cheaper than the store bought aquarium pendants and such. Is there a reason, (color temp or something) that they are not talked about or used in lighting aquariums?


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## BryceM (Nov 6, 2005)

I think all mercury vapor lights are yellow, with a very low Kelvin rating. If you're interested in saving money, try a hydroponics shop. You can find perfectly good equipment without paying fish-store boutique prices for it. Much of it ends up getting used for less-than-legal growing activities, if you get what I mean. I would stick with Metal Halide though.


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## QuantumCranker (Oct 9, 2005)

Mine looks like that one...maybe a tinge bluer...er (more blue)


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## bpimm (Jun 12, 2006)

QuantumCranker said:


> Mine looks like that one...maybe a tinge bluer...er (more blue)


My brother and I both used them years ago with decent resulst, They're not the best to look at color wise.

Brian


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## ruki (Jul 4, 2006)

Mercury vapor and metal halide produce light by slightly different methods so they have different resulting spectrums. These are related to fluorescent tubes, so I included them too.

*Mercury vapor*
Put some mercury into a tube. Heat it up a bit (when the lamp first starts) so you get mercury vapor. Pump high voltage through the mercury vapor atoms to add energy to its electrons. When the mercury vapor atoms lose this energy, they emit photons on exact known wavelengths. That's what gives them their blueish/green color. Use some glass to block the ultra violet wave lenghts that are also produced. Color choices are limited to just one, you just get the mercury emission lines. These are not opimal for plants. A kelvin rating makes little sense for this bulb.

*Metal Halide light*
Start witha mercury vapor lamp. Add other stuff to the mercury, specifically metal halides. These are compounds with one atom from the halide column of the periodic table (Fluorine, Bromine, Chlorine,...) and one atom of something else. Don't coat the tube with phosphors. Now light is produced as several elements get excited and emit electrons as they lose the added energy. Perhaps these should be viewed as the next generation of a Mercury lamp. Color choices better with emissions from various halides added to the bulb. Kelvin ratings work better than one would think for this sort of bulb. Think this is due to the concentrated hot part of the bulb having more thermal characteristics than mercury vapor or fluorescent bulbs.

*Fluorescent Mercury vapor*
Start with a mercury vapor lamp. Lengthen the tube. Coat the tube with phosphors which has atoms that get excited by the photons initially produced by the excited mercury vapor. Each phosphor emits light at its own set of emission frequencies. Perhaps this should be viewed as the twisted (actually physically stretched) son of the mercury lamp. Color choices are excellent with all the phosphors out there.


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## erik Loza (Feb 6, 2006)

My LFS had some pendant mercury vapor lamps made by Giesemann over a big tank for a while. Very neuveau looking powder-coated bell-shaped reflectors with a remote ballast. The build quality, of course, was top-notch but as others have pointed out, there was a strange color cast to the lamps. They were PAR-based bulbs did not seem very bright for their size. Furthermore, the bulbs had a frosted interior, so there was no point light source like an MH lamp would have. The light output seemed to me like that of a PC lamp with poor a poor CRI. In other words, why go this route when you could have MH for the same $$$? MH just offers a lot more for what we are doing, I think.


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## BryceM (Nov 6, 2005)

Nice description ruki. Thanks.


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## bpimm (Jun 12, 2006)

erik Loza said:


> why go this route when you could have MH for the same $$$? MH just offers a lot more for what we are doing, I think.


The reason I used them years ago was simple

MH 175 Watt $300.00
MV 175 Watt $30.00

I used the phosphor qoated version they grew plants but had an odd color. there would be no question if they were the same price

Brian


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