Thanks
They're running at 33.5V and 620mA each so just over 20W.
In terms of efficiency these are supposed to be 119 lm/w (90 CRI so the PAR is probably higher than the lumens would suggest) at 37.3W and 85C. I've estimated I'm getting around 133lm/w by running them at 20W and water cooling them to a surface temp of 46C. TBH this is all theoretical and it doesn't really matter to me what extra efficiency I'm getting or could get. Why?
1. Without water cooling I'd not be able to run this many watts in such a small area in my loft. I can't get a big AC unit in my loft. So comparisons to air cooling at the same wattage are moot (for my situation).
2. I couldn't afford more efficient COBs at the moment. 250 of these Citizen chips cost me £550 delivered. If I went with 120 CXB3950s instead I'd be looking at paying at least £3200 on the grey market. The extra efficiency and power saving (probably around 10% going from 55% to 65%) would take a hell of a long time to offset that upfront cost.
My lighting energy costs £1660 per year. If I needed 15% less energy (1-(55/65)) to get the same results I'd save £249 a year... (3200-550)/249= 10.5 years for the CXBs to pay for themselves with efficiency savings over the cost of buying the Citizens.
I'd love to say I'll still be using the same setup in 10 years. Realistically that ain't gonna happen.
Edit: Just edited my power savings calc which I think was a bit off.