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Re: MH light questions

In Aquatic Plants Digest V2 #1063, George Booth <booth at hpmtlgb1_lvld.hp.com>

>I have MH light experience and initially looked at hydroponic
>fixtures.  A few observations:
>1. Hydroponic fixtures were cheaper than "aquarium" fixtures.  Duh!
>1. Most of the hydroponic fixtures we looked at exhibited a loud 60 Hz
>hum from the ballast when running.  I don't know if this was brand
>specific or due to cheaper ballasts, but I wouldn't want one in my

Hmmm. I didn't notice during any of my recent visits to the local hydroponic
shop which has at least 5 HID lamps burning. I'll have to pay more attention
next time. It's possible they've made some sort of noise baffle to alleviate
this. Then again, it's also possible that the fixtures you looked at were of
an older (noisier) design or possible were old floor models that had
developed a problem with the ballasts?

>2. The reflectors were smaller.  I suspect they are designed to
>produce a particular (square?) light pattern when mounted 5-8' above
>the plants, like in a green house. Aquarium fixtures should be (are?) 
>designed to be used a foot or so above the water surface. 

Actually, the advice from the local hydroponic shop involves having the
lights as little as a foot above the surface of the leaves and use fans to
keep from burning the plants with the heat from the bulbs. Other reflector
designs ARE made to be mounted much further away, but to still focus the
light on a fairly concentrated area.

>3. Neither reflector exhibited any kind of sophisticated design
>(parabolic or whatever). They look more like a design based on "the
>easiest thing for the sheet metal shop to knock out in a hurry".

At least one reflector at the local store (working from memory this time as
the catalog isn't readily available) has a dual parabolic design that
appears similar to the description of the PL reflector that was discussed
here last week.

>4. Aquarium designs are a bit more attractive than hydroponic designs.

There certainly isn't anything particularly attractive about the hydroponic

-- dj