Bottom line is they are more efficient than anything else to date. Very low wattage and yes, they penetrate very well. What appears dim to the naked eye still has the potential to cook stuff on the sand bed that isn't ready for it.
People who return their LEDs before they give them a chance are short changing themselves. Some corals and anemones have taken months to acclimate. many months in some cases. They do acclimate eventually. You can view my tank thread for proof.
There are many misconceptions circulating around the internet about LED
A PAR meter is not accurate on LEDs (200 PAR out of a LED
unit will cook things that were under 200 PAR from T5 or halides IME), and no article on the internet
has actual PUR measurements from any LED
fixture. Most of the ones I have read state things they have absolutely no data to back up.
Also, many folks believe you need multicolored LEDs to grow and color up corals. Most of these people are the ones who sold their fixtures and went back to the old lighting.
This has been proven to be false information as well.
All you need are dimmable fixture(s) that you can adjust over time. As stated, place new additions strategically, so that they don't get blasted with light, no matter how dim your fixture looks.