I make 3 catagories of LEDs for this hobby:
1)Moonlight
2)Power Actinics
3)Regular Main Light
A)LED is mostly driven by low voltage so when the light fell in the tank it won't shock your fish nor yourself.
B)Most LED can dim even my moonlight now can be dimmed
C)LED can be scaled very closely to the wavelength you need. What wavelength you need? I wish some marine scientists will step up.
D)Light generated by LED is very low heat and in most cases will not heat up your tank so controlling the temperature in your tank become much easier and save a lot of chiller usage. Temperature is a major factor in tank disasters!
E)For the same wattage of energy supplied, LED technology generally output 2.5 times light than a fluorescent bulb.
F)With Power Actinics, the wavelength is quite pure and thus your coral looks sharper than the actinics you get from PC, T5, VHO that are base on plasma fluorescent. You see a white haze using the fluorescent technology while you see pure clear blue water when using LED.
Conclusion:
Anyone can debate about the viability of the mainlight as almost not a single marine scientist has told the public about the exact wavelength that the coral needs(mind you that agriculture scientists have proven LED is 80% more efficient than the MH).
Power actinics is "clearly" winning the actinics race. For those non believer's, they should just see it for once, and they will change their hearts. One can tell with their own eyes in a split second-no need to wait for the coral to grow and tank to crash to tell the difference like the main light debate.
Moonlight, I find no better choice than LED at all.