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Metal Halide Lights

In Digest V2 #1059, "Shimoda, Wade" <WShimoda at hei_com> wrote:

> I have several questions about MH lighting.  I read what I could find in
the archives
> but still have these questions.  I'm thinking of using them over a 90 gal.

First a caveat. I've never used metal halides personally, but I've spent a
good portion of the last couple years looking into setting up a marine reef
tank with such lites and I've also been looking into their use relating to
hydroponics in the last month or so. Take my perceptions for what they're
worth -- well researched but untested in reality.

>1) Could anyone describe their success (or failure) with using MH lights
>from a hydroponics supplier?

>2) Or what about MH fixtures as used in warehouses, or even the smaller
>ones used in retail spaces?

I question how different either of these would be. While some new advances
have been made in HID lamps (Sodium Vapor and Metal Halide) recently that
can make them even more usefull for growing plants, most of the practical
advances made have been applied to flourescents as not nearly as many people
are using the more powerful lighting systems for plant/aquarium use.

With respect to the lighting systems availble from a hydroponics supplier, I
pulled out a catalog from a local store. It lists three types of metal
halides and three different types of sodiums in various wattages in four
different types (brands?) of lighting hoods. 

Here's a quick run down:

Standard Metal Halides: Bluish-white light. 4200k. Available in 175, 250,
400, and 1000 watt sizes.
Agro Sun Halides: Hybrid halides that work in standard halide systems.
3300K. Available in 400 & 1000 watt sizes.
Daylight Halides: "Virtually duplicates natural sunlight". 5500K & 6500K.
Available in 250 and 400 watt sizes.
HP Sodium Vapor: Orange light for stem growth and increased flowering.
2100k. Available in 150, 250, 400 & 1000 watt sizes.
Son Agro Sodiums: Hybrid sodium w/ 30% more blue. 2000K Available in 160,
270 & 430 watt sizes.
Enhanced Sodium: Icreased blue & higher lumen output. No temp rating.
Available only in 600 watt sizes.

I would think that normally only the daylight halides would be useful,
however there may be situations where some of the other bulbs might be
useful. The hydroponic supplier also has sodium conversions for use in
halide systems and halide conversions for use in sodium vapor systems.

>1a) and 2a)  Are either of the above available with a remote ballast so
>that I don't have to hang the extra weight from the ceiling?

Three of the four lighting systems have remote ballasts and all four have
water resistant plugs for use in humid greenhouses.

>1b) and 2b)  Are there safety concerns with these non-aquarium fixtures
>that I should be aware of?  (e.g., UV radiation, non-containment of
>shattering lamps, etc.)

Two of the four systems have the ability to attach a safety shield to
protect bulbs from accidental spray & to help keep their reflectors clean.
The same two systems also can attach a cooling system so that cooler air
from outside the growing area can be brought in to cool the bulb and then
piped out again. One of the reasons for this is for greenhouses that use
supplemental CO2. A third system actually has an optional light diffuser to
keep from burning plants if placed too close to the leaves of the growing

>3) Which type of fixture would work best over an open top tank?  The
>boxy type that usually come with a couple fluorescent tubes, or the
>pendant type?
>I'm particularly interested in learning whether or not the reflector
>designs for non aquarium specific MH fixtures reflect light across a
>narrower or wider area than aquarium specific MH fixtures.

The system I mentioned in 1b above that has the optional light diffuser has
an adjustable reflector so that the light can be focused onto either a very
small area or diffussed over a much larger area.

>4) Why do the aquarium MH fixtures use universal (vertical or horizontal
>mounting) lamps rather than those specifically designed for one burning
>position?  Is this just a way for the distributor to stock fewer lamps?

I don't know. One thing I notice from the bulb replacement specs is that for
the standard metal halides where the hydroponic store carries both
horizontal and universal mount bulbs, the horizontal mount bulbs have
approximately 10% higher initial lumens. However, for daylight halides
(which is what we'd use for aquariums) the bulbs are only available in a
universal style so perhaps that is the only way they are made.

>5) Are the ballasts for universal lamps different than those for
>vertical or horiz. lamps?

They don't appear to be.

>6) The ads for the lamps don't indicate CRI.  Are they all the same, or
>are some better than others?

There are some significant differences in the way the various lights look,
however I have never seen a CRI for any of them. 

>7) Finally, are there any recommendations for how many (and what
>wattage) MH's would be sufficient for our 90 gal.?  Is there a fixture
>available that would allow me to use just one stronger lamp to provide
>light across all 4' of the tank?

Well, for what it's worth, for hydroponics a 250 watt system is sufficient
for a 3'x3' to 5'x5' area. However, from various messages that I've read
here, it appears that half or more of the light that reaches the surface of
the water is reflected away, but once the light penetrates into a tank,
almost all of it is reflected within the water. So I would guess that you
would want the 400 watt system. For comparison purposes, the 400 watt 5500K
Daylight Halide is listed as having 32,500 initial lumens while the 6500K
version has 29,000 initial lumens. Also, the 5500K bulb costs $94.95 while
the 6500K bulb costs $104.95.

I'd be interested to hear what you finally decide on. If you don't make
regular updates to the list, please consider e-mailing me.

-- dj