Discussion of ideas is the reason I frequent this board - and why i steer clear of Facebook
That and coral porn
As for the question, I think that the 250 watt Radiums will be very good for the reef. Based on everything I've seen I think that there is a difference in the way that Acropora respond to directional light as opposed to the more even bathing of light that T5s produce. You will need to start off with short photoperiods and work your way up, but 250 watters are pretty safe over a tank your size and with wide reflectors. In my opinion Radiums are the gold standard.
Now this is speculative on my part, and its based on a lot of reading of anecdote mixed with some par testing. I don't have any proof of what i am theorizing here.
I believe I have seen a pretty good consensus that very evenly diffused light sources like T5s can produce a lot of light, but both my personal experience and through those of others there is rarely, if ever burning of corals of the kind that happens under MH. "Why is that?" I've had corals in PAR approaching 600 without that happening, and I don't do the whole "move it up slowly" thing. I've even had an LFS owner who deals in thousands of frags tell me that if its under T5s just put new frags wherever and they will be fine. When I first got my 8 bulb fixture I put it 5 inches off the water over a reef that had been under-lit with LEDs and went to full photoperiod, no issues.
I saw one other lighting system with the same thing - the LANI LED panels, which have very diffuse light and generate pretty high par. A couple of big tank setups from Europe have reported that they ran the panels at 100 percent from day one, no burned corals.
Under MH (and especially LED), why do corals burn? I've seen enough PAR tests to conclude that a coral placed under each type of light is probably receiving roughly the same amount of measurable PAR, perhaps even more from the T5 tanks.
One Idea I had was that the differential between the light coming directly from the bulb and the reflected, diffuse light of the reflector that surrounds the MH bulb result in areas of coral with extreme photosynthetic activity immediately next to areas with much less photosynthetic activity. To use an analogy, the MH is like cooking with a broiler while T5 is like baking in an oven(And compact LEDs are like cooking with a blowtorch). The even light of the T5s results in a more gradual drop off of light intensity striking areas next to the tops of the corals.
"Baking" the coral all over may not lead to visible damage like burns - but the overall high level of photosynthesis induces changes in the coral's energy budget, and if there is too much light the coral may abandon production of pigments that function to enhance the use of light in lower light conditions, the coral may have a difficult time restraining the reproduction of Zooxanthellae and become browner/duller, or may even produce protection pigments that dull the coral. I have seen corals turn darker/browner after increasing the amount of light - thats opposite of the accepted though that higher light induces lightening of corals.
I have more along these lines but if you have read this far, thanks for hanging in there
If you have, let me know if any of this makes sense...
