Just wanted to throw in my 2 cents and since I am new, you can take my opinion with a grain of salt.
I started this hobby just 4 months ago, I have 4 SPS now. 2 montipora, 1 acropora, and a green birdsnest. The montis started to bleach from the light when at the top of the tank, and grow like weeds mid tank. The birdsnest doubled in size in 2 months, great growth/color, and sits at the top in the middle (brightest spot) The surf n turf acro sits next to the birdsnest, and although small and new, shows signs of liking its placement/light.
Now...the big opinion. My first LED was a blue/white only and the bulbs were very concentrated, and the lenses were very narrow. I never ran them at full power, just 50%, cause I could bleach everything easy, and started to. I switched lights to a full spectrum Ocean Revive Arctic S026. Couldn't be happier with this light. It spreads the LEDs out across the whole tank, has a much wider lens, and I am able to run it at 80% of full power. I also keep it almost 12" off the surface of the tank, and I keep my tank covered with a lid. When you have a less concentrated LED bulb placement, it allows you to run your lights at a higher level. Any coral that is high up in the tank that is getting hit by a direct beam has a better chance of bleaching, hence why I chose to keep my fixture very high, and not blast at 100%. LEDs are just more powerful, and a much different light source than MH. (My experience with MH comes from a hobby other than reefing
....but close)
When you run an LED, it shoots concentrated beams of light down and the water does not disperse it much. You really don't need a light meter unless you want to dial it in absolutely perfect.... I just put mine on to 75% and watched closely. If they start losing color, your lights are too bright, or certain coral is in the wrong spot. If they don't lose color, ramp it up little bits at a time until you find the sweet spot between losing color, and not enough light. Better safe than sorry, so I run mine low, and keep the fixture high, with glass in between. The glass, ability to dim, and fixture height is my safeguard against bleaching/loss of color (one in the same to me).
I might be a newb, but that seems like common sense to me. Just look at the posts and a lot of what I said is confirmed by peoples experience and comments. MH has a very very wide spread and a wide hot spot compared to LED's. Each LED is a hot spot, and spreading them out is crucial I think. The downside of course though, is that because each LED is a hot spot, my "full spectrum" light does not evenly share every spectrum with every part of the tank. I feel like that factor right there is what makes a MH fixture have a slight superiority when it comes to color/growth. With that said now, I think in the future, LEDs will take over the market and MH will be a thing of the past. Its just not perfected yet.
On another note, my LPS, softies, zoas and palys go nuts under the LED, but none can sit high in the tank. They all sit at the bottom, except a war coral in the direct middle, or if up higher, off to the sides.
