how do you figure out your lighting needs?

[underwatermonsters]

I have a 125 gallons long tank and would like to know what is the best type of lighting i should get. I would like to have hard and soft corals but I'm not sure if they would cohab with each other.

I've read that the correct way to measure a lights intensity is by lumens or lux. I've also heard from other aquarist that the lighting for a reef tank should be around at least 2-3 times the number of gallons you have in watts. So which is it? Should I go by the amount of lumens or Watts.

If anyone can point me in the right way thanks.

[GKarshens]

I am by no means a lighting expert, but I also have a 125 (6'). I am using 3 250w SE MH bulbs. I am growing soft, LPS and SPS. I find the hardest part about keeping all 3 is getting enough flow for the SPS without blowing away the others.

[caferacermike]

I'd go with what GK is saying.

75g with 2x250w 14k Phoenix and 200w 20K power compact supplemental for color.

For a mixed tank I'd say the 18" rule for a 250w bulb would be good to follow. So the idea that 3 bulbs would each throw out about 18" of good intense lighting would be ideal for a 125.

I prefer using PC or T5 lighting to accent my halides. I like having them come on before the MH and stay on after the MH go out to help prevent sudden light shock. Also I think it's asking a bit much of one bulb to make you happy with growth, color, etc...

[GKarshens]

Good point. I forgot to mention the Actinics

[Jimbo]

I have a 110 (5') lit with 2x250SE halides and 220W VHO Actinic. I did a bulb change in October and increased the number of SPS I have in the system. It seems that the SPS I had before the light change does fine anywhere in the tank, but some other types are suffering in low light. I have been moving many new frags and colonies up higher in my rock work to compensate, but that gives my tank a very unbalanced look. For a tank your size I'd look into the 250DE X 3 with supplimentation. I think (hope) you'd get more penetration to the lower levels of your tank, since the 250DE is closer in comparison to a 400SE (please someone correct me if I am wrong).

[Wryknow]

Lux /lumens is really the only way to say how bright your lighting is with any authority and even identical lighting systems will vary some by tank, based on factors such as bulb age, water clarity, etc. The 3-5 watts/gallon rule is convenient but frequently misleading as watts is a measure of power consumption and different types of lighting use power more efficiently than others. Unfortunately, this means that you will need to rely a bit on anecdotal evidence to steer yourself in the right direction for lighting.

My $.02 - choose either a metal halide or T5 system for your primary lighting. I just haven't had the same results with fluorescent or compact fluorescent bulbs (although they can be good to supplement.)

If you want to have a canopy/hood on the tank then I would prefer to use the T5 just because of heating issues but many people use MH bulbs in a canopy and rely on a chiller to keep the tank temperature down. A good T5 system will cost just as much as a good MH system.

There are a LOT of different types of bulbs but generally speaking the lower the K of the bulb, the more PAR it will produce. The lower K bulbs produce a more yellow light though and many aquarists prefer a white, or even blue, light for aesthetic reasons.

The number of bulbs you need will depend on the bulb types, reflector quality, what you're keeping in the tank, and where it is in relation to the bulb. Most folks recommend using one MH fixture for every 24" of tank but this is not necessary if, for example,you don't put any coral in the middle of the tank!