Buy a Mars II is a big mistake and will end you spending more money!
My experience with Mars II 900W (5W Epistar chips)
After a lot of research I decided to get the marshydro mars II 900W, as I though it was the best quality price product out there, and despite my little space (0.7m X 0.8m) and after talk with a marshydro staff member I decide better too much than too less!
After all at this stages I never readed that an excess of light could harm the plants.
The light arrive fast, well packaged, and seems sturdy and well made, very heavy dough.
I plug the light and the brightness was just amazing! no way you could look at it without sunglasses!! (in fact after a day I ordered a glasses tinted specially to look through the red leds of those lights and don't harm the eyes and also see the true color to identify possible nutrient problems)
The sound was pretty loud (more than the expected) and so it was the heat (compared to an 400W classic metalhal).
So,first problem (in part my fault) I had to add a bigger extractor fan to palliate with the heat this monster makes.
After this change all when smooth and had a very,VERY productive harvest (15 hours trimming,with that I tell you all!)
The second run,well... I will not enter in detail to not make this even more large, but it was a complete disaster, the plants suffer to grow, did not side branch well,foxtail even in the main cola...
And at the 3rd grow after all the possible re adjustments and LOTS of headaches and money spend I find out thanks to a friend that the lights did loose most of is power !!!
For me it was unnoticeable, as I was watching them several times a day, but my friend immediately pointed to my, and after testing with the luminens par meter I was astonished to see the results, a 68% luminens down!!!
My last grow it was somehow succefull, thanks to an industrial quantities of CalMag,a good pruning and keeping the lights at no more that 20 cm, what it produced hot spots with is consequences, some blanching in the top colas,etc.. An unnecessary pain in the ass!
So, please learn from my mistakes and get another brand or even better, build your own!
I am in the process to re-convert my mars to c.o.b.'s! is the way to go!!
And philips is about to release a new horticultural led.