How much UVA?

@Grow Lights Australia did a pretty comprehensive study on this and determined that uva ran all day was more effective than uvb ran in increments at increasing secondary metabolites

Blue brother said:

@Grow Lights Australia did a pretty comprehensive study on this and determined that uva ran all day was more effective than uvb ran in increments at increasing secondary metabolites

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..pretty much why I am asking how much UVA I should be looking to supplement with

When on 12/12 ( after 4-5 week of flower ) I begin a 10-15 minute cycle every 4th hour .
So about 3x during a 12 hour flower. I haven’t tried any other cycle , so I guess one could experiment.

I didn’t want to fry them so I started at 10 minutes then moved to 15 minutes max. At least for me.
I use one of those cheap peg timers / easy to set intervals.

UpstateRecGrower said:

..pretty much why I am asking how much UVA I should be looking to supplement with

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Sorry I can’t find the thread to link it to you but if I remember correctly the appropriate dosage (watts/m2) is discussed in depth. And in answer to your other question about how we measure it I’m pretty sure it is in watts like all other EMR

UVB doesnt increase THC levels and is degrading nearby materials in the room. UVA can be used in small amounts (like 2 % contiously). That will also change plant shape, make the more compact.

Blue brother said:

Sorry I can’t find the thread to link it to you but if I remember correctly the appropriate dosage (watts/m2) is discussed in depth. And in answer to your other question about how we measure it I’m pretty sure it is in watts like all other EMR

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Thanks for the mention. Here is a link to the test you're referring to. There are links to other tests in the same thread.


UV radiation is measured in milliwatts. The Nichia UVA diodes we use are over 70% efficient. UVA diodes are cheaper, much more efficient and have a much longer life than UVB. Our lights have about 1% UVA (<400nm).

my plants seemed to mature faster under uva LED. i ran a uvb light for about an hour with no other uv or uva. plants all took super long to mature...extra 2 weeks or so, even the indicas. my last grow the plants would almost ready day 58 and were perfect by day 65. this last one, they were cut early at day 77/78. different strains, but all of them were like this.