I have a 4x4 grow and using one 1000 watt hps and also have a 600 watt that I currently have a 10k bulb in. I'm not really impressed with how dense the buds are after harvesting a couple plants and am wondering if I should switch to the using horticulture hps in the 600 watt? I already have 600 watt bulbs in 3k, 6.4k, and 10k so money for buying isn't a factor. Also I have plants ranging from week 1 - 6 in the flower room.
How hot is your grow room? That could be the reason for the lack of density. 1600 watts for a 4x4 space is going to create a ton of heat. Especially when one bulb is a 1000W HPS and the other is a 600W 10K MH. The 10K is definitely the hottest running bulb in the Sun Pulse lineup. I run only Sun Pulse bulbs and have great results with very dense buds. We need to know more about the setup with regards to venting, and all the other important parameters that can impact flower formation and density. It could also be genetics. Some strains don't have dense buds. Ever. It doesn't mean they aren't dank fire. Some strains are just like that. But, in my experience, a hot grow room is usually at the heart of whispy buds.
I'm not sure what you mean by 10k. The amount of lumens? If so, that is extremely low and probably would you didn't get any dense buds. I recommend a Sunmaster HPS 600w bulb for your application. Any brand will do but that one has 85,000 lumens and the proper spectrum for flowering growth. Metal Halide would be a lot better for Vegging but that is only if you have the extra money for it.
The 10K is the Kelvin temperature rating. The light he is talking about is rated at 10,000K. It emits higher levels of UV light and is intended for the finishing stages of the flowering cycle. I use them in the 250W, 400W, and 1000W sizes. They burn hot as hell, and you have to remove the glass from any hood you may have it in. Otherwise, the glass absorbs most of the UV light. Metal halides can flower just fine. I just finished trimming a few plants harvested today that were flowered under 3,000K Sun Pulse MH lights.
I read the UV light of a 10,000 Kelvin bulb can be used throughout the whole flower cycle to help with trichromes and that's why I have it in there. 3k plus 10k color temps are suppose to give the best light spectrum. It's in a cooltube though so maybe the glass is blocking the UV light and it's just being wasted? I think I will just switch it to an hps bulb. Also the 10k UV light is a sunpulse, and my hps bulbs are lumateks. Also with 1700 watts my grow room ranges from 71-78 depedening on the temp outside.
I just replaced the 10k MH with the 3k HPS and the HPS is running much hotter then the mh, had to turn on another exhaust fan to keep the temps down.
I'm still mad that I wasted 600 watts for a few months on a UV light that was being blocked by glass...lol I think whether hps and mh runs cooler all depends on your ballast and bulb because in my experience I've seen mh's run cooler then hps's and the opposite way around.
I have heard that 10K is best when used for the last week to 10 days or so of flowering and yeah, unfortunately they cannot be in a glass enclosure otherwise the uv is wasted. I still can't test one out until I get an air conditioner because like many people, I need to air cool my lights just to keep a decent temp in the room, and it still gets a little warm in there...