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Metal Halide + Lens = No UVB?

JJ Bones

Nug of the Month: Feb 2013
Anyone heard of the glass blocking the UV-B spectrum of the metal halide?

Just recently read this, found it pretty interesting. If it is true, then it's pretty important to know for those who use MH for the last two weeks of flower.

JJ Bones

Nug of the Month: Feb 2013
No, UVB helps produce more trichomes because the plant attempts to use trichomes as a sun skin so to speak.

MH normally = more potency while HPS normally = higher yields

The MH has more UVB than HPS which causes more crystals. So some people like to use MH in all or parts of their flowering cycle as a way to get the best of both worlds and receive potency + high yields.

However if it is true and the lens from a reflector blocks the UVB, there's almost no point to use MH in flower unless you aren't using a lens.

JJ Bones

Nug of the Month: Feb 2013
Well, genes play a major roll in potency. However some put MH in flower for the first two weeks and last two weeks, switching to HPS in between.

I read this in Ed Rosenthal's newest book.


New Member
if you want uv-b, i wouldnt rely on MH bulbs.. (normal uvb outdoors is 350+ u/nm)
**try iguana mercury bulbs for uv-b, any of the single 150w+ setups can cover 4x4

and yes, the glass does filter/block some of the uv-b emitted from the MH.



New Member
The reason the Metal Halides are helping is their Blue wavelengths.

Blue is good for potency.

UV is close to blue on the spectrum as well.
So, the reason it may work to increase is either it is damaging and the plant protects itself. Either way the adding of the MH helps in the the last days. If you have both a MH and a HPS I would put both on if that makes sense with your situation.
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