LED lighting is advancing as a type, but it isn't quite there yet. We couldn't find an LED solution that was a perfect fit for the tank, so we went with metal halide from Aqua-Medic. I'm currently working with the manufacturer of the Orphek LED light to fine tune the optics and add some dimming features, but these developments take time. I will have some new optical lenses later in the week for the Orphek fixture I have. It is the brightest and widest spectrum LED on the market, but it lacks in the control department and with the current 90˚ optics it is too bright in the centre of the lighted area, a victim of its own success. The white LED is 16,000K with a 14,000K available soon. This is substantially higher than the 7,000K white light used in most LED fixtures.
Dimming is difficult with LED, as the spectrum can shift and compromise the CRI and PUR value of the light. An alternative option is to use more drivers and timers so just a few white LEDs come on for dawn and dusk simulation. True dimming is better because it allows you to change the look of the lighting without losing part of the spectrum. There is a patent in place for LED control that is slowing the development of aquarium lighting.
There are a lot of metal halide lights on the market that are fancier and certainly more expensive than the Aqua-Medic fixture we picked, but none that I would deem better. I have used Giesemann fixtures that are very similar and almost twice the cost, but I found the magnetic ballasts to be noisy and they don't offer energy efficient electronic ballasts. Sfiligoi and a few other companies make some nice looking high end MHL fixtures, but none of them offer a 6' fixture with 4 x 250 watt HQI lights. Aqua-Medic has discontinued the 4 x 250w fixture, but they were kind enough to find two refurbished units in their warehouse. I spoke to Thomas (the new president of Aqua-Medic USA) about putting the option back into their line and he said he would do so if there was a demand.
We tried Aqualine Buschke 20,000K bulbs in the fixture and it was too blue and eerie looking. It currently has 14,000K Phoenix bulbs, it is still a little too blue. The plan is to go with Aqualine Buschke 13,000K bulbs in the three fixtures for a total of 12 x 250w. We may mix in a few of the bluer Phoenix bulbs for variety. Having 24' of reef with uniform lighting may be less natural looking than some variation.
In summary, the Aqua-Medic fixture worked out to be the best practice for the following reasons...
1) Cost effective initial cost. Some of the LED options would have taken years to pay off with energy savings. We will have the cost and inconvenience of annual bulb replacement, but it's still a cheaper option in the long run. We have piece of mind that it will not have PCB (printed circuit board) corrosion or overheating issues that shorten the life of some LED lights.
2) Low profile for maximized access to the tank for servicing.
3) Electronic dual ballasts for energy savings, silent operation, and less clutter. These have proven to be a very reliable product over the years I have used them. Electronic ballasts from other manufacturers have proven to be hit and miss.
4) Over-heating has not been an issue with Peter's tank. The fixture we have in place now is mounted just below the cooling exhaust duct and it acts as a heat sink. The radiant heat hits the metal duct and gets cooled by the passing air.
5) Compact reflectors. While many people like oversized reflectors, I find that the block access to the tank and cast too much light on the viewing panels and sand where there are no corals. With the Phoenix bulbs, we have 150 PAR at the centre of the tank substrate, and a close 125 at the viewing panels. There isn't much of a drop off or hot spot even with the fixture mounted close to the surface of the water. Oversized reflectors wouldn't fit in the area we have to work with and they don't allow any room for T5 actinics to be mounted in the same fixture.
6) Tempered quartz glass lenses that can be cleaned regularly. This is an area that is grossly overlooked by most hobbyists. Why pay top dollar for lighting upgrades and new bulbs, only to lose much of the light through salty glass. Peter's tank is acrylic so we also need to keep the acrylic top clean and clear.
7) There are no fans to fail, make noise, or collect dust.
8) Product reliability. I have used Aqua-Medic fixtures for over ten years, and they have been on the market with the current design for quite a bit longer. Replacement parts can be purchased locally or from Aqua-Medic USA in Colorado.
9) There are only three plugs on each fixture, one for the 4 x 39 watt actinic T5, and one for each dual HQI ballast. We can locate the 6 ballasts remotely to keep the tank cool and keep the electrical equipment safe and dry. It doesn't offer the dimming features we were hoping for, but the only company that has MHL dimming control with dawn & dusk etc. is Sfiligoi and they are $1,000.00 each, they only do one bulb, so we need 12 of them, and they are plagued with reliability issues. We will have the actinic and MHL lights come on from one end of the tank to the other, on offset timers, for a sunrise-sunset effect. The 6 HML ballasts give us 6 zones.
10) The Aqua-Medic fixtures offer natural looking light with calming shimmer. The tank lit by the light is bright and very uniform. The sand is a touch blue, but we have lots of HQI bulb options to choose from.
11) Versatility. If a new dimmable metal halide ballast comes along in the near or distant future, we can just plug it in. If more efficient MHL bulbs come out, we are ready, I just hope they are double ended HQI
Osram's ceramic HCI Powerball MHL look promising. They just need to come out with some higher colour temperature models. LED technology has raised the bar for lighting solutions. Now it is time for MHL to play catch up.
One area where the Aqua-Medic fixture is lacking is moonlight. We will add some blue PAR38 spotlights or change the onboard T5 ballasts for dimming ballasts and run the lunar cycle through the profilux controller. We currently have dimmable ATI T5 actinics in our fixture, but we don't have a ballast that dims yet.
You now have the burden of being a WORLD CLASS build! 
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