I use a 315w 4200k ceramic metal halide for my indoor growing, in a 3'x3' enclosure. I can offer a little bit of advice about this light.

First, the "medicinal" growers seem to have reached the consensus that 315 watts of CMH is more or less equivalent to 500 watts of HPS. Not a "scientific" assessment, but since the "testing" they do has measurable results, I'll buy it. You can use that to help gauge the coverage you need, or go by their other recommendations about coverage for this light: 2.5'x2.5' to 3'x3' to provide enough light for flowering plants, or 4'x4' to 4.5'x4.5' for vegetative growth. Even though you aren't growing what they are, these guidelines should still be helpful to you, because you are growing plants that have a "full sun" requirement (and that flower).

The UV light from this bulb is excellent, and is part of why I chose it. The 4200k has more UV, and still has MORE than enough red and far red to make flowering plants happy. The 4200k vs 3100k for CMH is not similar to MH vs HPS when comparing spectrums. At all. This has a little to do with the higher operating temperature (ceramic arc tube) and a little to do with the extremely efficient low-frequency square-wave ballast that runs the bulb. Both CMH bulbs will work well for both vegetative growth and flowering. I like the 4200k for its higher UV and its lesser spikes in a couple places that aren't as appealing (I think yellow and IR, if I remember correctly). Again - the 4200k still has tons of red and far red.

CMH bulbs (at least the 315 watt ones) are rated for open fixtures, which means they have a secondary protective filament casing, and are considered "self-extinguishing" in case of lamp failure. You do not need a protective layer of glass enclosing your light fixture.

The other thing I will mention about the CMH is that the usable bulb life is significantly longer than that of a MH or HPS. 2 to 4 times (or more), depending on whether you like to replace your bulbs at the beginning, middle or end of the recommended replacement window.

My most recent completed grow under this light was basil, and I have to say those essential oils were plenty strong!

Thanks ills step - those are some nice looking basil plants! It looks like you also supplement with 2 LED's?

The basil has really tight internodal spacing - looks great, Is the tight spacing and good growth due primarily to the CMH? Have you grown without the LED's? Just wondering what contribution the LED's make?

Also, my understanding is that the CMH ballast is in the reflector. So, if the ballast goes out one would need to take the entire unit in for repair to a reputable dealer?

Any idea if there is a 1000 watt metal halide bulb rated for open fixture that would provide the UV?

If I could find that running the metal halide/ HPS that I have alongside a CMH should give good results (and perhaps not render my MH and HPS so obsolete)!

Thanks for your help!

Brian

Those are actually not LEDs, they are window fans. My solution for air exchange in the enclosure (the front panel was removed just for the pictures) was to mount those so that they blow straight up, drawing air from inside the enclosure up and out (and deflected away with those angled panels). The internodal spacing is a result of the CMH.

The Sun System CMH (they brand it as a LEC - Light Emitting Ceramic) does include the ballast inside the fixture. If something breaks, I suspect you will need to contact the supplier for repairs or a replacement. There appears to be a warranty, but only on the bulb. That being said, my own experience with Sun System products has been a good one so far (no issues).

There are also other places that you can find the 315 watt CMH with the bulb/reflector separate from the ballast. I think Sun System offers a CMH with a remote ballast. Cycloptics Technologies has one - the Greenbeams reflector/ballast combo. And there are some others. The reflector used with the Greenbeams is supposed to be especially good.

The only open-rated MH bulbs I've found are not marketed for growers. You can find them if you look, but be careful - many are not rated for universal positioning (and may have to be mounted vertically, for instance), and some have some sort of UV-blocking built into the outer envelope (not great for your purposes). I'm afraid that's about all the information I have to offer about those.

Thank you illsstep. That is a really nice set up. I will look into the CMH options you list. Have you ever tried the 2 bulb - 630 watt cmh system?

Thanks!

Brian

I have not myself. I do know that running the bulb horizontally is supposed to result in a slight spectrum shift (not sure how much that matters though).

I have also heard from some people that love them, and others who wish they had gone with 2 315's instead of a 630 because 2 light sources will provide better coverage (due to overlap and more multidirectional light) than the 630 in its single reflector. If I ever upgrade my setup, in terms of size, I will definitely choose more 315's over the 630's for exactly that reason. Multiple light sources are a big benefit when growing indoors, in my opinion. I have taken several steps with my current setup to mitigate the negatives that come with my single light source (I've added reflective walls and "stadium" style risers under the pots to raise the outer edges to mitigate the lower light intensities there).

Hi illsstep -

Thanks for the info. I thought that perhaps there could be some destructive interference with two light bulbs close together in the same reflector.

Thanks so much for your insight. I really appreciate the exchange,

Brian

Hello illsstep -

What about the use of the following as a source of UVB and UVA?

http://www.petco.com/shop/en/petcostore/product/reptile/reptile-heating-lighting/zoo-med-powersun-uv-self-ballasted-mercury-vapor-uvb-lamp#

Not sure how many watts of UVA/UVB one would get out of it vs how much heat? Just curious as it seems you get the most light intensity out of a 1000 watt metal halide/1000 watt HPS system but of course no UV. If the below item or something like it can provide the UV then in principle both UV A/B and light intensity could be maximized?

Thanks!

Brian

Honestly, I couldn't tell you. Supplementing with UV is not something I have personal experience with. Anecdotally, I have heard of people supplementing with the UV bulbs designed for tanning beds. I haven't seen this one before, but like you, I would be worried about how much of the output would end up being in the form of heat rather than the UV light you're looking for.

Thanks illsstep!