It's a lie that a 315 CMH will match or beat a 600w HPS on yield. Flat out lie. Just like the flat out lie that LEDs, even the most efficient on the market, can beat twice the watts in HPS.
What is true is that it puts out a better spectrum and will result in a higher quality final product.
The best LEDs are about 20% more efficient/better than HPS. So 1200w of HPS would be roughly equivilent in light output to 1000w of CXB LEDs. Again though, the CXB will put out a better spectrum, so better quality.
The most cost effective option for lighting tends to be HPS + supplemental to match the better quality of other lights. Adding 6500k and UVB bulbs to HPS will give you a better spectrum than CMH, CXB LEDs, or fancy HPS bulbs.
If the 20% extra heat from the HPS is problematic, switch to the CXB LEDs and depending on color temp you may not need 6500k, but the UVB would still be required for best results.
I currently run HPS + CMH (I got a hell of a deal) + Tanning bulbs (UVB). Next upgrade will be to add CXB LEDs.
The CMH lights are very nice and work very well. The only issues I've seen are where someone believed the lies and undersized their lighting for their space. 3x3 is about the max size for a 315 CMH alone for flower.
CMH is actually less efficient than HPS. This is a fact. It puts out less lumens and less par watts per watt of electricity used.
CXB LEDs are the way to go if you want a lower power light to compete with a higher power light. They will allow you to run the same amount of light with 20-30% less power used, but will cost you an arm and a leg to buy, just like the CMH option.
