Rethinking Lighting

[dbsherwood]

Hi folks,

I just wanted to run my thoughts by you regarding the lighting approach in my tank and see what people thought.

My tank is ~650 gallons, being 7' long, 4' wide, and 3' tall. The overflow on one of the short walls of the tank adds another 1' to the overall length of the tank (8x4x3) but isnt' of concern when it comes to lighting.

My current lighting situation is that I have four 6' vho fluorescents and 3 400W 10K Metal Halides over the tank. The 3 400W 10K metal halides are in lumenarc reflectors that look somewhat similar to tetrahedrons and do a very nice job of focusing the light down into the tank.

My live rock is set up to run down the center of the tank and is roughly 2 feet wide at the base. The metal halide lights do a nice job of lighting the live rock, and the light stays off the sand and the acrylic. The tank is open on 3 sides, and if you look down the tank length-wise, the swimming tracks for the fish are noticeably much darker than the reef itself. I currently am not running the fluorescent lights as the sit to the outside of the pendants and do a nice job of helping coralline algae grow on the acrylic.

By typical measurements, I have about 2 watts per gallon of water when I just use the metal halides. However, if we think of the tank as just the area being lit given the reflectors, it comes out to about 4+ watts per gallon. The vho's would add to this, but not that much considering their light is very diffused in comparison to the pendants.

Does this make sense to everyone as a way to think of my lighting? My realization is that by going with the metal halides pendants I get optimimum metal halide lighting, but at the sacrifice of the fluorescent lighting, as that lighting is obstructed by the reflectors (everything is mounted in a canopy). My only other choice for the fluorescents would be to move them down to be just to the sides of the reflectors, but that begins to bet pretty complicated.

My other option is to to to 1000W metal halides in the reflectors, but that seems like it might be a touch too much.

Thoughts?

Thanks.

 

[Anonymous]

If you are only looking to grow corals on a 2ft strip of LR I would tink you are good like you are. If you are wanting to increas the area you can grow things then I think you will need to go with 6 fixtures. If you are wanting to lighten up the sides you could add a few VHO bulbs.

 

[Anonymous]

I think watts-per-gallon is a fairly useless measurement when thinking about reef lighting. The two important factors are aesthetics and livestock health. If you like the look of your tank, and you have sufficent lighting for the livestock you want to keep, then you have great lighting. I wouldn't stress about pursuing any (ultimately meaningless) watt-per-gallon ratio.

 

[Anonymous]

If you look at the AA article where sanjay compares reflectors you can see the total illumination of stuff as you go from 1x1 to 3x3 areas, beyond that though to a 4x4 area you almost double the amount of area over a 3x3 area, so expect about half the light. But as mentioned if you're interest is corals on the rocks you should be good to go, corals on the sand could work too as those sometimes are the less light demanding ones.

 

[Unarce]

I think watts-per-gallon is a fairly useless measurement

I hope so. I'm only at 3.6WPG, which used to suggest I could only keep softies :lol:

 

[SnowManSnow]

bah!

the thing i don't normally see mentioned in lighting threads is CORAL DEPTH and light spread. I can have a 100g tank and keep 10 VERY healthy SPS corals directly under a 250w pendant! Just keep the light hungry stuff in the photospread of your lighting system and you'll be ok.

b