2 Lighting Questions

[Warnberg]

I got my lights (MH 250 watt X 3 with XM 10k bulbs). Now I am designing the hood. How far should the lights be from the surface of the water? I am thinking 10 to 14 inches. Second, what kind of photo period should I run with these? I will be supplementing with 54 watt T5's.

Thanks,

 

[mflamb]

Sounds like a sweet setup. I also am going to use 3 250 MH 10K bulbs. My plan is 14 inches. My reason is I'm not using glass under the bulbs so I want splash room and the higher the bulb the less heat exposure to the water. I would supplement with t5 instead of pc for less heat. Just my opinion.
Mike

 

[markandkristen]

mine is around 12-14 inches with 175s and its perfect.
im running vhos for supplement.
but with xm 10k's 12-14 is ok ..... just because they are a super bright bulb. i had the 175watt version and they really lit up my 90 ... i can only imagine what how bright 250s will be.
what kelvin supplements of t5s will be used?

 

[Warnberg]

I'm was planning on using the Giesemann 54W Pure Actinic 03 T5 HO Fluorescent. I have several 54W bulbs now and will be playing with them to get the color I want.

 

[mflamb]

I'm also going to use actinic 03 t5. I think that's the best mix. I have not really decided on photo time for each. I'm going to ask the guys (and gals) that have good looking tanks what they're doing. No need to reinvent the wheel, if you know what I mean!!!
Mike

 

[mattliu]

why not put them about six- eight inches off the water. you spent the money on the 250's why waste the light. by halving the distance from the bulb to the intended surface you quadruple the intensity. spider reflectors compare favorably to even a lumenarc III when measuring the par on a 3' x 3' foot surface at six inches, so most of the light should be directed down into the tank. if you raise the bulb up more, it becomes even more important to use a well designed reflector to focus all the light down into the water.

of course heat will be an issue, more radiation will be enter your water, but fans should be able counteract the heat transfer that's not in the form of radiant energy coming from the bulb, so water temp. shouldn't be a real issue.

as far as maintenance issues with this setup, you're at an advantage being the designer. as far as bulbs shattering from fish splash, there's at least two other people in the area that have them under 6" with no problems.

 

[Warnberg]

Great points everyone, I have toyed with the idea of 8 inches off the water surface. If you had an acrylic tank how far from the surface would you put them? Would you still go 6"? I got the reflectors from John's place, I believe they are spider reflectors.

Thanks all,

 

[mattliu]

the melting point of acrylic is 266 degrees farenheit. i don't think at 6 inches you would have to worry about melting. here again, extra heat besides light should be able to be blown away. the continual thermal contraction and expansion would probably lessen the life of the acrylic, but probably not much more from 6 versus 12.

http://www.reefkeeping.com/issues/2003-06/nftt/index.php

this article addresses the issue of blowing too much air over a halide. basically it's a moot point. to be sure throw out a thread in a larger forum.

i assume you are going to have the light positioned above the cut outs ?

 

[Warnberg]

Two of the three lights will be over cutouts, the center light will be over the brace in the center. I wasn't worried about melting the acrylic, what I am worried about is weakening of the glued joints. Thanks for the article on cooling, it gave me some additional ideas on cooling the hood.

Funny thing is, the T5's I have actually got me thinking about the glued joints, the cutouts in my tank have a "lid" that fits over them, they are basically the cutouts with additional acrylic pieces glued to them to keep them from falling in. Well after a year of T5 heat one has lost two of the glued on pieces. Needless to say the covers for the cutouts are not longer on the tank.

 

[mattliu]

i see what you mean. better safe then sorry.

 

[mflamb]

mattliu, Points well taken. Mine will be suspended by chain from my metal stand/hood frame...very adjustable. I'll experiment. I ordered my tank with 3 openings/ 2 cross braces, so nothing is in the way.
Mike

 

[Warnberg]

Well I started designing my hood and now I need to clarify some things.
1) the spider reflectors, what is the best way to mount them direction wise? Bulb back to front or bulb lengthwise to tank?

2) When you say lights 8 inches above surface, do you mean bulb, reflector portion closest to hood or reflector closest to water?

Make since?