Yeah some pretty negative ''help'' around here.
A 315 is similar to 500w of hps. W for W it seems like you will lose out but likely won't.
Firstly the spectrum on the 315 is better for the plants and although it will give 100W less yield over 600hps the quality will be far better.
Second is heat management. Although 315's efficiency puts out comparable 500W.. they don't run that hot so will save on cooling. The more important point is temp management. It will be easier to keep 315 in the right temp zone, the plants will produce more yield and quality than using a 600hps with temps too high. Regardless of what you plan to do with the end product higher quality smoke will always get priority. With that said a well grown shit strain is still a shit strain, contrary to popular belief it is possible to polish shit ;p.
The 315 bulbs are not cheap, If you can, get a blue and a red. Use the blue strictly for veg and red for flower. Some people would suggest using the blue for 2 weeks into veg as well but given the longer prior veg time hours the blue bulb will be doing too much of the work and degrade faster. This will eventually hurt yield in the long run since the bulb will be doing a worse job at vegging/growing roots. You should replace both bulbs once a year, this is a happy medium between long term quality and over heads.
Cobs and led's are good but they come with pro's and cons. Although W for W they are the same as a 600hps in terms of heat (not technically true) the cobs and leds send the heat up into the air and into your outake. Because of that your canopy temps will drop under cob vs hps.. however you can run your canopy temps a little higher with cobs anyway, around 80-85 fine. The downside with cobs comes in colder months, the canopy/root temps will drop too low and yield will suffer a lot, a damn lot. So then you need to supplement heating directly countering any savings you made in the summer months on cooling. Regardless of time of year it's always better to run lights over as much of the night time as possible. It gives plants the best chance at staying cool during summer and warm during winter.
The way to hold onto most of those savings is to use a thermal fan cut off unit. A basic on/off one costs about 30-$50 and will cut off the out/intake when temps get too low. You still may need to supplement some heat even with the fans off but it will save a fair amount. All you need to be aware of is that the heating is enough to kick the fans on about once every 30 min to an hour, they will only stay on for about 5 min then cut off again as temp drops to your limit (70f root zone). This way you keep replacing co2. You may ofc lose a little yield if co2 levels are not keeping up but this should be a choice of responsibility. The alternative is continually blowing heating out to waste, for your size setup that would average about 2 to 300W waste 24/7. When the fans are off you will also see some condensing, having a de-huey is a must. It does however give off a fair bit of heat in operation so although it's costing W to maintain RH it is also heating the room. Still, it's going to run at a loss.. just far less than blowing out hot air 24/7.
Quality, yield and running costs, Cobs and cmh W for W are about even if you consider such annual details above, imo. Hps should be walked passed unless on a budget.
