Design of lighting canopy?

[anna]

I am just collecting all of the bits for my new tank and am about to start the construction of my canopy.

2 x175 MH
2x 110 VHO

75 G tank (19.75" deep).

2x 4" fans for cooling

4" sand bed

The house has AC.

I could use some help in determining the offset from the water to the bulbs.
I get a distance of 21.75 inches from light to sand with a 6" offset
and a 25.75" with a 10" offset.

My goal is to eventually put clams on the sand bed.

Any thoughts on optimizing light intensity vs. heating loads would be helpful.

Anna

 

[Len]

This is probably not the help you are looking for, but anywhere from 6-10" is just fine. The higher up the bulb, the less intensity per given area but the more coverage it provides (and vice versa). But with 2 halides and 2 VHOs, you'll have plenty of lights for clams and most sps over your tank .... enough that I wouldn't fret much about it either way.

Personally, I'd go for 10" and use a good reflector like PFO's parellel or Spiderlights. With the use of reflectors, the light loss due to the inverse law becomes a lot less of an issue and you can mount the halides a bit higher without appreciable loss. The higher up the lights, the less heat transfer as well.