Bulb distance from acrylic

[kimmeewoo]

I've been searching for the appropriate distance for 250w MH bulbs from the acrylic for an hour now, with no luck. I know the info is somewhere around here, but I can't find it!

How much space should be between the bulbs and the acrylic? The bulbs are 250w and the tank is 55g.

[icemark]

http://www.reefland.com/cgi-bin/foru...&threadid=2953

Based on that formula from Iwasaki: just under 16 inches

[RH]

this is the equation in the link given by icemark

Minimum Distance in inches, Bulb to top of tank glass/acrylic = 1/2 the square root of the bulb's wattage.
I got 7.9" from this equation for a 250w bulb. I think you don't need to put it double the distance away even though u have 2 bulbs. ;;

[Ninong]

kimmeewoo ~

I like the formula icemark posted as a safe, conservative distance from the center of the metal halide lamp to the top brace of an acrylic tank. (I believe icemark probably forgot to divide by 2 when he suggested just under 16" for a 250w lamp. ;))

Anyway, that formula would yield 7.9" for a 250w lamp and 10" for a 400w lamp. I'm sure you could reduce that distance by 2" for a glass tank without harm to the tank.

Tenecor offers a reef-tank combo in either 120-gallons or 150-gallons (48x24x24 & 48x24x30) and they make the acrylic canopy for those tanks 12" tall to accomodate metal halide lighting instead of their usual 8" tall canopies which are designed for VHO lighting.

Many people position their metal halide lamps closer to the water than that and they can get away with it provided that they do not place the lamp directly over a brace (glass or acrylic). Here are two horror stories that popped up on the boards in the past 18 months or so: hobbyist "J.R." loses a 450-gal custom acrylic tank because he positioned 400w 6500K Iwasaki lamps in Spider Lite reflectors only 4-5" above the acrylic center brace and it failed within 24 hours, and hobbyist (on Reefs.org) loses brand new 240-gal Oceanic tank within 24 hours because he placed 400w 6500K Iwasaki lamps only 3-4" above the center brace.

It is definitely a good idea to try to position metal halide lamps so that they are not directly over any top bracing, if at all possible.

Ninong

[icemark]

Thanks for the catch Ninong and RH... math always was my weak subject (along with spelling, grammar, celestial physics...)

I hate the thought that I gave a bogus answer.