<a href=showthread.php?s=&postid=7183348#post7183348 target=_blank>Originally posted</a> by hahnmeister
The penetration of T5s is double that of halides, due to the linear output. The intensity just depends on how many bulbs you use. T5s should have no problem lighting a tank as tall as 36" or more...in fact for most T5 users, I would suggest a tank at least 24" tall, since the intensity they carry can melt lower light species that normally get placed on the bottom...open brains, mushrooms, etc. T5 means you need a taller tank to get the same light gradient as a shorter tank with halides, as the light penetrates 2x as much. So with a shorter tank, you could get stuck with one intensity throughout the tank, making a mixed reef where the top is SPS and the bottom is mushrooms near impossible.
Heres an interesting comparison...
With a common aqua-green open brain coral (lobo or welso), I can place it on the sandbed of my 60g cube with a 400 watt halide, HQI ballast & lumenarc reflector with a 14,000K aquaconnect bulb. OR, frags of that same coral go in a 40B with a single 250wattHQI halide 14,000K pheonix. Either way it does just fine with the halide.
When I tried to take that same coral and put it into a 40g Breeder with only 4 39 watt T5s (6 was too bright for other things even), it retracted and began melting.
I mention this because its not so much wattage or PAR when comparing halide to T5 as it is looking at how that bulb gets the light to the coral. I can cite that vs. a single halide pendant, there is much more light that hits the coral with T5s, as with halide, the point source makes my SPS shade themselves in many areas, and so one side of a colony could be nice and colored in, and the other half faded. With T5, the PAR could be less, but the output is coming at the coral from a wider angle, meaning that the coral gets more use of the light that is there.
Also, some tanks just lend themselves better to T5s, and others to halide. A natural tank for T5s is a 55g. It works great with 4x54watt T5s. The height and norrow profile of the 55 works great with T5, where with halides, dual 250s seem to be needed (thats 2x the wattage) due to the height, but much of it is lost on the narrow profile of the tank, etc. Then there is my 60g cube. Its 24" dimensions would mean that I would have to sun something like 8x24wattT5...and at that, I still wouldnt get the intensity I would with a single lumenarc/halide. Not to mention the cost of replacing all those short T5 bulbs (T5s cost nearly the same per bulb no matter if they are 2' or 4', so economics favors the 4'). The 60 cube shape favors the halide pendant.
The best way to chose is to make a thread/post in a thread with your intentions for livestock and the tank's dimensions. Then people can make suggestions based on that or post pics of simlar tanks with either setup.
You can also never go wrong with a combo of both T5 and halide. Some of the best results I have seen...for instance a 120g with 4x54watt T5 and dual 250 watt HQI halides...grows anything like a weed.
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