Hello... I asked the same question just a few days ago of Marinedepot.com... here's their answer... "
Thank you for contacting Marine Depot. The Current USA Truelumen Pro Striplight LED?s have low wattage (0.2W) diodes. While they are very bright, they do not include optics or reflectors that would provide enough penetration to sustain corals in deep tanks. Current USA suggests that you can keep some SPS corals within the first 12 inches under the water line, and other easier corals such as soft polyp, leathers, mushrooms and zoanthids within 18 inches.
Depending on the dimensions of your tank, Current USA recommends at least 4-6 LED strips for mixed coral reef tank. Unfortunately, we do not have any test results of lumen or PAR ratings, but they would not replace the output produced by your metal halide and VHO setup as far as intensity and water penetration goes. I would recommend the Ecoxotic Panorama, Orphek PR156W, or the new Kessil LEDs coming soon as an alternative. Each fixture outputs approximate a 2 feet light spread so depending on the length of your aquarium, you may need additional units for complete light coverage. "
Also, LED lighting isn't measured by wattage but by lumens... and to get the same light to the bottom of your 55, like my 55 reef tank, the cost is twice that of matel halides. I'm running 2, 175 watt halides and 2, 100 watt VHO's at 750 bucks for the Hamilton hood and to do the same thing with LED's, I just found out yesterday, would cost 1400.00 dollars. Until the price becomes reasonable LED's are out of my thinking.