So unlike all the speculation, I have actually owned 2 XR15 and now SKY.
Here is my tank (Waterbox 100.3.... 36x24x22) when I had 2 XR15 blue with diffusers. I had the diffusers because I could see the disco. In particular, note the sharp shadow on the right front side. Why is there a shadow? Because the lights are only along the center line of the tank. I tried mounting the lights both "left right" and "front back", no change due to the optics normalizing the spread. The issue is that the light is only so big front to back. 24" tank vs ~5.5" of light front to back.
In order to alleviate the shadows, I added LED bars. At this point I also was not happy with the amount of blue-green in the spectrum. I added the A360X for the shimmer and the violet. Note that the shadow in the image is now gone. So it took adding the LED bars to the XR15 to remove this effect. At this point the XR15 were turned down to ~50% due to all of the extra light sources.... so really absolute par does not matter so much when you start having to add extra light sources.
Eventually I was sick of the mixed controls, so I just said to heck with it and went Kessil with led bars. Great coverage and the Violet biased color that I wanted (vs the blue-green of the Radions). Even here though ,the A360x's are only at 50%.
I did not like this mix of bars.... lights... etc. Just wanted to simplify. Here it is with 1 Sky.
So the coverage in a real tank is similar to 2 XR15 plus 2 LED bars (Reef Brite XHO). That is not speculation. That is real world. You can look at all of the empty tanks in the world and try to draw conclusions, but until it is on a real tank, with real aquascape and corals, it does not really matter.
But...But.... But..... How dare I say such a thing? It has a lot to do with the science in that diffuser. One thing overlooked by many is what is stated in the original patent. When the LEDs that we use are shining, they have a very large emission zone. ~ 80-85 degrees from normal (that is if the light is shining straight down, light also shines to the side up to 80-85 deg from straight down). Any light that strikes the water to glass interface at an angle greater than 63 deg is transmitted through the glass. The diffuser plate has these round cut outs whose geometry blocks all of the direct light coming out at an angle greater than ~60 deg. The light beyond that is channeled into the acrylic and mixed into a diffuse source. The end result is that you get a combination of direct and indirect illumination. Kessils and Radions are 100% direct emission. There is light that bounces off the glass, but alot is also transmitted through the glass. The Radion diffuser helps, but it does not do as good of a job as the mixing plate. So combining a large LED array with this mixer tech results in a very uniform illumination. This is best seen in a real tank with obstructions, not in an empty tank.
Now some shimmer movies. I do not know if these will play or not... Is it pure Kessil shimmer? Absolutely not. It is more than the Radion with Diffuser... I would say similar to what I was seeing withthe 2XR15 (w diffuser) and A160.
In the end, I am not going to say that one sucks... or another sucks... but the amount of speculation resulting in misinformation is astounding. If you are going to make a claim, make sure you have the real life experience/ evidence to back it up. It really gets old to hear all of these false claims without backing... the mixing panel being reused... the soft coating getting sticky... the light being ready to fail at the first sign of moisture... the heatsink being cheap and never tested... I do not know why you are on some personal crusade to paint it in a bad light. And don't say the whole "Ohhhh marketing is claiming" Yeah... If you run 5 XR30 over a 6 ft tank at 60% each because of the coverage, you can replace that with 3 SKY. Also if you don't agree with the marketing, that does not give you the right to make stuff up and spread it like truth.
Price??? Yeah... XR30 just had another price bump before the SKY was released. So if you want to point your price anger at someone, aim right for Ecotech where the price for an XR30 + Diffuser is now $926.... $56 more.
These are all great lights, and in one situation or another each would be better. For a mixed reef like mine, you are either going to be running 1 SKY, 2 XR15 with LED bars or 2 XR30 mounted front to back. So yeah.... 1 SKY is equivalent to 2 XR30 in my real world case.
Loving the real world examples here. If I were to buy a Sky on my next build it will be because if this.