Damn, I thought you had figured it out. I'll seriously try to explain, because it's a good concept to grasp when looking at cobs. This shit is tricky.
Efficiency, as quoted by manufacturers, is expressed in lumens per watt, right? What's a watt? It's a measure of power, how the electric company bills you, and is calculated by multiplying current by volts.
Watts = current times volts.
So power is what interests us. Watts. Let's look at Vero 29 numbers:
View attachment 3668055
And let's choose the 1050ma column. You'll see in the "Typical Watts" column we have 38.2W. That is 1.05A x 36.4V, which is 38.2W. And at 38.2W we make 5985 lumens, or 157 lumens per watt. This is all at 25C.
Now the CLU048-1818 is 35.7V at 1050ma and 25C, just trust me on this I'm looking at their spreadsheet right now. So we multiply 1.05 by 35.7 and get 37.5W, right? A little less power usage than the Vero 29, but here's the kicker. It makes 6133 lumens, and if you divide lumens by watts you get 164 more lumens per watt! Or 7 more lumens per watt than the Vero 29.
More lumens, less power.
The 1818 is trickier because it's 52V, so at 700ma it uses about the same watts as the Vero and 1212. And it makes 172lm/w at 700ma, so even better.
I really hope this helps.