@canadiankushman this is the best place to discuss the lighting you asked me about.
The Philips 860W CDM lamps are the same tech as 315W CMH. The 315W lamp has gained a lot of popularity recently because of whichever improvements. The efficiency difference is entirely in the ballast.
First, don't be fooled by the 860W moniker; a magnetic ballast running on 208V will deliver that wattage and the lamp will happily run on it. However, most people run 240V single phase or 277V three phase and with those inputs the standard magnetic ballast will output 1000W, and the lamp runs fine on it.
Magnetic ballasts run at the standard alternating current (AC) line frequency of 60Hz. This is why they're necessary for this lamp, because it won't run on high frequency digital ballasts. These will not drive the lamp to its maximum efficiency but will still give good results.
To get maximum efficiency with these or any other HID lamp, one needs to use a square wave ballast. It's this square wave output that's the efficiency secret of the 315W system.
There are a few low frequency square wave ballasts that output 1000W, including the Hortilux Platinum and the BadAss ballasts. Both of these are now out of production, although I've managed to scrounge a couple BadAss ballasts. They work great!
One last consideration about the 860W Philips lamp; it must be operated in a vertical orientation, either base up or down. For this reason I felt it was an ideal lamp for vertical gardening and I ran them in vertical socket bare lamp fixture.
Because I'm working to improve performance and efficiency in indoor gardening, I've since moved on to LED lighting of my own design. I'm now looking to sell my inventory of both of the above lamps, if you or anyone is interested.
I'd recommend these lamps as a way to provide high quality results with reasonable yields and as such is an excellent stepping stone on the way to much more expensive LED lighting.
There you have it; far more than you ever wanted to know about a light bulb!