Lighting question

[jkburn88]

I have a 90 gallon reef lit by a Sunpod 2 X 250w 14K MH fixture. After reading reviews, I thought this light would be adequate on its own, but that's not the case. It produces "cones" of light which don't cover the entire tank (especially high up on the sides). My corals always seem to be half in the shadows, and two large montipora caps have grown out of the direct lighting and the new growth doesn't seem to be doing as well.

I've decided to gut the original canopy that came with the tank and build in the Sunpod along with two VHO bulbs. My question is, will this be enough light for a heavy SPS tank, and should I go with daylight or actinic bulbs? All opinions welcome!

 

[Tomoko Schum]

I have a 120 gallon tank with two 250W 14K Phoenix bulbs over it. My tank is an SPS dominated mixed reef and everything in it seems to be very happy and growing very fast. So I think 2 x 250W 14K light fixture should work just fine for your 90 gallon tank. How high is the light fixture suspended over your tank? I have mine suspended probably 5 or so inches above the water surface right now (I lower my light fixture as my bulbs age and lose their intensity.)

Tomoko

 

[8BALL_99]

2x250MH is more then enough for a 90. Problem is not all reflectors are created equal. Try rasing your fixture up a couple inches to increase the spread. You really dont' loose much light just by increasing the air cap between the tank and light.. What cuts into the light is the spread. Some fixtures you raise or lower them a few inches and it effects the light in the tank a ton cause you get to much spread. I've got 2x250MH Ice cap pendants over my 300 and even with them at 19" above a 25" tank I get 250 par on the bottom with 10k bulbs

 

[jkburn88]

Thanks for the responses. My lights sits about 4-5" off the water (on the legs it came with). Sounds like I need to use the hanging kit and raise it up. I didn't know you could do that without reducing the par too much.

Thanks again,

Ken

 

[Tomoko Schum]

Actually 1 inch can make a difference in PAR, but if you don't have a really light demanding coral, you may not notice the difference.

I gradually lower my pendant type light fixture after my bulbs are a few months old. I have noticed that Some corals do respond positively to the increased level of light.

Tomoko

 

[gflat65]

Plenty of light. I might think of T5's as a replacement for the VHO's, though, unless you already have the VHO set up. I'll be switching to T5's for supplementation across the board as I need to replace VHO bulbs. Supplements can help pull everything out of the dark/shadows.

 

[8BALL_99]

<a href=showthread.php?s=&postid=14091674#post14091674 target=_blank>Originally posted</a> by Tomoko Schum
Actually 1 inch can make a difference in PAR, but if you don't have a really light demanding coral, you may not notice the difference.

I gradually lower my pendant type light fixture after my bulbs are a few months old. I have noticed that Some corals do respond positively to the increased level of light.

Tomoko

This is more due to spread though then just the air space. It all depends on how your reflectors are. My current pendants sit 20" above the tank and I get very good par on the bottom of the tank.. With my old reflectors more then 5"-6" off the water and the par fell very quickly. Since his fixture produces "cones" then his reflectors put off more of a spotlight. So raising them up some shouldn't hurt his par levels much if any. Some reflectors are ment to sit higher up then others. A 250 watt Mh focused into a spotlight can very easily give you to much light in the upper middle of the tank.. 2x250Mh over a 90 should be plenty without having shaded area's.

 

[Tomoko Schum]

A good reflector makes a huge difference. I don't have any disagreement with that. I have seen it myself. Over my FW planted tank, four 55W PC's with two German MIRO reflectors produce a far better result than a Coralife fixture with four PC 65W bulbs at the same distance. The difference in terms of plant's photosynthesis levels and resultant growth is remarkable.

With that said, the inverse square law of light applies to a MH (a point source) bulb with an ordinary reflector as well as to a MH bulb with a good reflector. As the distance between the source and an object doubles, the intensity decreases to 1/4 of the original intensity. Raising your light fixture will give you a better coverage, but the intensity will drop proportionately whether you use a bulb with a poor reflector or a bulb with a good reflector. However, if you have a great reflector to start with, you will have more light than you do with the same bulb with an ordinary reflector no matter what the distance is.

If the places high up on the sides tend to be shaded, you might consider placing less light demanding corals to that area. If your sunpod fixture is like my Aquamedic pendant fixture, you will have some shaded area due to the cone shaped light pattern of the reflectors.

Tomoko

 

[8BALL_99]

I really wasn't comparing good reflectors vs bad ones.. Just some focus the light while others spread out the light. If you take a reflector that focuses the light and raise it up a couple inches higher then a reflector that spreads the light more the light level in the tank ends up being around the same. A very good example is LumenBrights vs Lumenarcs. You mount lumenbrights a MIN of 16" above the tank vs Lumenarcs that you mount at around 6-8". But they both produce the same Par levels in the tank with the Lumenbrights even having a little better numbers on the bottom. Both are good reflectors but the focus the light different. Since one produces more of a spotlight you have to raise it up twice as high to get the same coverage.. Even with raising it up twice as high you still get just as much light/par as you do with the other reflectors sitting 6" off the water.. Hope that explains it better.

 

[Tomoko Schum]

Actually I did not think you were comparing good reflectors vs. bad ones. You were pointing out the light spread vs. the distance from the water from the very start. I made the comparison since I know that the common pendant style light fixtures, such as Oceanlight, Sunpod, etc., do not come with great reflectors unfortunately. (Sorry, I should have made my points clearer to avoid the confusion.) I chose the overall appearance over the value of reflectors so I just have to put up with it for now. I prefer the sleek and modern look of the pendant fixture for the decor I have in the room. Raising the pendant does help with the light spread albeit it lowers the intensity. When I lower the pendant, the brightly lit area becomes smaller definitely making the left and right ends of the tank shadier. If I get to upgrade (it's a matter of finding a good cabinet maker), I consider a Lumenbright mini 3DE HQI reflector. I need to find out about the minimum distance on these since it is significantly smaller than the regular Lumenbright.

 

[8BALL_99]

Ahh I understand. You are thinking his reflectors aren't that great so a couple inches might matter more with that reflector.

I'm not sure on the Mini what the distance is. You for sure would need to know that before you build your canopy. It might not be that much difference though. BTW the guy that is married to one of shannons friends that I told you might be interested. Well thats a no go.. They are in the middle of a divorce :eek2:

 

[Tomoko Schum]

Oh, shucks, but I understand.

I really need to walk over to my neighbor across the street and ask him if he can help me. He is a super furniture/cabinet maker. It's his hobby. His German grandfather was a professional cabinet maker. He told me that he grew up helping his grandpa.

I will find out about the mini before I do anything. Its dimension is much smaller than the regular Lumenbright. I don't know if the manufacturer did anything to its design to compensate for the disadvantage of the smaller cone in terms of the light spread. I may end up with Luminarc reflectors instead after all, though. We shall see.

Tomoko