Thoughts on T5 versus metal halide:

[Julie]

The largest difference in my little opinion and experience has got to be that the electronic ballast is much cooler for nearly the same light, however, the MH below 175 is almost pointless and unfortunately, MH's are very hot, so consideration must be given to cooling the surface too.  (wear long sleeves)

Having said that, the MH gives a much more realistic light that can never be produced with flourescents, but at that depth, you could almost use them interchangeably. And for reasons I do not fully have researched, MH still requires a little flourescent assist to meet everythings needs in a reef. please elaborate
This way you get full coverage, the delicate sunny shimmer, and as has been pointed out, the ability to do the dawn/dusk lighting that is not possible with MH alone. Don't forget about actinics too, as you'll want something for overnight as well.

[babblefish1960]

I was suggesting that at this depth, the t-5 will have enough punch to meet the requirements of most things down there other than the real light hogs such as brains etc., so in this light, they can match an MH, just not much deeper.

Perhaps gvv can bail me out here on the purpose of using both types of lights, as the MH does fall down a wee bit with some of the growth requirements for lighting.

I did indicate that the research I have done in this area is scant and I feel inadequate to properly address the question, I just passed along the notion that this does seem to be a thing that is commonly being done to care for something.

If nothing else, the flourescents can be used to provide the dusk/dawn lighting as well as noon-time higher lighting for a couple of hours, giving a more realistic and balanced spread of light throughout the day for your reef.

[Julie]

I'm so tempted by the t5 - have you seen June tank on the month on reef central?

Brains are sand bed under halide.

[gvv]

One comment about MH DE lamps - you should have UV shield with them - simply it means you should have glass cover in your canopy.

Regards