Lumenbright's focus the light more like a spotlight and need to be mounted pretty high to get good coverage. You would have to experiment, but the reflector mounted about 18" above the water would be a good starting point. I assume your looking to use 2 on a 4' tank? I use 3 Lumenarc's on my 125 mounted 12" above the water.
Analyzing Reflectors: Lumenbrite III, Lumenmax Elite, Lumenmax, and Lumenarc III
"The reflectors seem to fall into 2 separate groups, Group 1, the Lumenarc and the Lumenmax and Group 2 comprising Lumen Brite and Lumenmax Elite. The Group 1 reflectors seem to be better at providing a wider coverage, whereas the group 2 reflectors tend to focus the light slightly more creating higher peak values and smaller spread.
The lumenarc III and the Lumenmax reflectors provide a large area of light coverage and hence are more suitable for tanks wider than 3 ft. At similar distances they both provide a large coverage of area where the PPFD values reach between 100-200 micromoles/m2/sec. In my experience, if a user can achieve PPFD values of 75-100 at the bottom of the tank, then they will have enough gradation of light in the tank to find places to keep most photosynthetic corals happy in the tank. The Lumenmax reflector at 30" provided a larger area where the PPFD values were greater than 200, as compared to the Lumenarc reflector. Hence, the reflector will be able to provide a higher intensity deeper in the tank, thus making it a better choice for someone looking to light a wide tank that is deeper than 30", or for providing the ability to grow higher light corals lower in the tank.
The Lumenbrite and Lumenmax elite are more suitable for tanks 3ft or less in width. They tend to provide a more focused coverage and higher peak values than the Lumenmax and Lumenarc reflectors. This can allow for better use in taller tanks, as more light can reach the bottom, or allow for higher placement of the lights thus reducing the heat dissipating in the water, or allow for higher light values to be obtained lower in the tank. This would allow the user to create a reef with a much lower rock profile. On shallower tanks 24" or less these reflectors would easily allow the user to move from a 400W lamp to a 250W lamp, resulting in savings in electrical costs."
I've read a little on dimable ballasts and personally don't see any advantage to them. I don't want dimmer lights...I want brighter lights.
I have my MH
ballasts in the basement next to the sump, about 6' below the tank and lights. I don't need the additional heat they put out going to the tank.