OK, I assume we are talking about being able to dim led fixtures, right? Well, good led fixtures will put out enough focused light to bleach your corals. A couple of years ago they didn't have dimmers so the only good option was to raise the lights higher off the water or lay screen or egg crate over the tank under the light. Also, most fixtures run 2 channels, one white and one blue. If you know what you are doing you run as much blue as you can and as little white as your eyes can tolerate. Blue is good for the coral, but not many people like a tank that looks like a windex bottle. The white light is for your eyes, the corals really don't want or need much white light.
Now, I wouldn't even consider an led fixture that doesn't have dimmers, or even better, built-in controllers so you can do a sunrise and sunset. You can get them either way. My 180g DT does an 8 hour sunrise, 1 hour at what I set as peak power and then an 8 hour sunset. I start the sunrise very blue and it gets more white every hour, then it is just the reverse for sunset. The last 3 hours are only blue leds and the corals seem to glow in the dark.
