# What kind of light do I need?



## Digital (Apr 4, 2008)

Right now on my 90g I'm running a Coralife 65x2 PC, and a T5 HO 54x1... The T5 HO 54w is brighter than the 130 watts of PC. T5 HO is known to be brighter anyway. I'd start out with a T5 HO and go from there.... With 216 watts you'd definitely need CO2....

I'm not running co2 yet on my 90g either...

6700k is perfect for plants, 10k is better if you want pretty colors in your fish... some people mix and match bulbs.

For the T5HO I have a Hagen Glo single bulb setup, got it off ebay w/o the bulb for around 100 shipped.


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## Hoppy (Dec 24, 2005)

A tank that is 18 inches front to back can't be uniformly lighted by a single T5 bulb sitting right at the top of the tank. Even a two bulb fixture will not cover the whole substrate area with even close to uniform lighting. You can solve that by raising the light fixture a foot or so above the tank, getting much lower intensity as a result, but much more uniform intensity. Or, you can use bulbs spread out over the top of the tank. With the latter you could use two to four T5HO bulbs, with individual reflectors, spaced around 4 inches apart, sitting right at the top of the tank, to get low to medium intensity. Or, you could use a 4 bulb fixture, with the bulbs close together, hanging about a foot or more above the top of the tank.

A few days ago I was able to use a PAR meter to measure the light from a 4 bulb Catalina fixture on a 5 foot long tank about 24 inches deep. I was surprised to find that at nowhere in the tank did I get 4 times the intensity that one bulb gives. This particular fixture had about a 2 inch wide moon light in between pairs of T5HO bulbs, so I expected to get 4X the intensity of one bulb right under the fixture. Instead I got 2X. The reflectors apparently give such a narrow "beam" of maximum intensity light that the light from each bulb doesn't extend out much from right under the bulb. Because of this, I doubt that all 4 bulb T5HO fixtures will give as much intensity as we have been assuming, unless they are raised high enough for the light to spread out.


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## moneylaw (Jan 30, 2007)

Thanks for the replies. I have one more question. It turns out my tank is 60x18x20 instead of 48x18x24. Which fixture will be better for the tank?

48'' T5 HO Aquarium Light 4X 54 w

OR

60'' T5 HO Aquarium Light 2X 80 w

basically I am wondering whether I can use 48" fixture with more watts on 60" long aquarium.
Thanks


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## Hoppy (Dec 24, 2005)

If you want to grow plants in the ends of the tank the 60 inch long bulbs are a better choice. In order to get reasonable spread from a two bulb T5HO fixture you need to raise it several inches above the top of the tank, but that reduces the intensity of the lighting. For that reason a 4 bulb fixture is probably the best idea for an 18 inch front to back depth tank. With most 4 bulb fixtures I believe you can run either 2 or 4 bulbs.


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## moneylaw (Jan 30, 2007)

Thanks, Hoppy


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## mcaquatic (Apr 26, 2010)

Does moneylaw have to use CO2 on the tank with the T5 HO fixtures?


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## Airphotog (Aug 21, 2009)

If he raises them up high enough and cuts the photoperiod down he will be on the edge.


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