Quote Originally Posted by OrionN View Post
I think it is a fallacy to say that 250 W MH produce more heat than 250 W T5. When one put 250 W/Hr for 10 hrs into a system, all of these energy will end up as heat, the same amount for MH as it is for T5. How efficient in lumen/ unit of energy of fluorescent (t5 is just a small tube florescent) vs. MH is debatable, but there is no arguing the fact that 250 W-hr input into a thermally isolated system will increase the temperature of that system by a specific amount whether you use a heater, or any type of light bulb because all of the light will end up as heat anyway in the end.

T5 vs MH bot can produce a lot of light but like any fluorescent lights, T5 bulbs need to be change every 6-8 months or so or else the light out put drastically decreases. MH need to be change every 18 months or so, the degradation is a lot less even at 18 months. The price of 250 W worth of T5 bulbs is high while the cost of one of the Chinese produced 250 W MH is less than 20 dollars with shipping, cheaper if I buy multiple bulbs. I can get 10 years of bulbs for the MH for a single change of T5 bulbs.

MH is a point source light, because of this reason, there is various level of light in the tank at various places. I like cube tank, very high light right under the bulb to keep my Magnifica anemone from moving and plenty of light for my SPS and clams even on the sand 20 to 24 inches from my 250 W MH (with a very good reflector). The point light source will also produce the shimmer effect that I love in a tank.

DE MH fixture is very small and leave my tank top very open to keep temperature down and great ventilation. My tank need no chiller with MH but will need one if I use a T5 base fixture that cover the tank. (93 g cube with single 250W MH)
My light is 10 inches above water level 250W DE MH with reflector, there is no salt creep or salt deposit on the glass of the light after about 8 months of use (lots of circulation in my tank with lots of water agitation). With T5 fixture, I always have to clean the light cover every few weeks or else the light output drastically decreased. After 8 months, My MH fixture is like new while a T5 fixture would be corroded, rusted and ....

I use Magnetic ballast for my MH which is essentially indestructibly and will function 10 years form now. I avoid electronic ballast due to this the possibility of it mal-function. You would be hard press to find an electronic ballast MH, T5, VHO or NO that still function after 10 years.

I like wide tank, 30 inches is my preferred width, so I use MH due to it being cheaper to start out with, produce the type of light that permit me to keep the tank better, look better more flexibility in keeping various animal in the tank. The light fixture (magnetic ballast) lasted much longer and bulb cost much cheaper to change. For me, MH is the number one and only choice. T5 is not even distance 2nd.
So very interesting comments, however there're two things I'd like to bring up. The first is that while yes, 250W is 250W, depending on the usage (for example 250W of LED would generate less heat than 250W of MH for the same volume of light, don't you think ?) may certainly generate the same heat, however you do not need 250W of T5 to create the same amount of light as a 250W MH from what I've seen so far. The second based on the information I've seen online is that you need to replace your bulbs on different schedules to the updates you've said :

T5 High Output (T5HO) - 9-18 months
Metal Halide - 9-12 months

That would mean that you'd need to replace the bulbs near the same amount, and for good quality bulbs on each, a single MH bulb can be anywhere up to 60+ dollars, excluding shipping. Sure I could get cheaper chinese knock off bulbs, but I'd not trust those lights above my tank, personally. Whereas the T5 bulbs are around 25 dollars each. Bringing the bulb replacement costs to near the same, if not a bit towards T5.

Very interesting comments though, and good note on the salt creep.