How much uv-a?

Hi guys.. and maybe gals

I need some help to decide and to understand how much UV diodes to add to my build. I can't seem to find a definitive watt per square meter or foot quantity as I can find for far red, for example.

I have a bunch of LG 365nm and 385nm diodes and I want to add them to 3K lm301b+xpe660 boards (from Alibaba). 730nm was already added at about 1w per sq/ft.

I have 2 main questions:

1. how many diodes/watts to use?
2. how much time a day and in what period of growing/flowering cycle would you use it?

also, I would love to have your opinion on how to devise the 2 wavelengths between the total amount of diodes needed.

I'm currently thinking of adding about 25pcs 385nm and 12pcs 365nm running at about 1-1.2w per diode to a 8x4...


Thank you

For a total 32 square foot... 44 watts of UVA... In my opinion...I would use more...lets say about 5 % - 7% of main light used minimum.... But of course you can use less. UVA in natural light is about 7% ...also it depends of location and altitude and time of the year...
I would use in veg and flower..just dimming it at same rate than main light

nachooo said:

For a total 32 square foot... 44 watts of UVA... In my opinion...I would use more...lets say about 5 % - 7% of main light used minimum.... But of course you can use less. UVA in natural light is about 7% ...also it depends of location and altitude and time of the year...
I would use in veg and flower..just dimming it at same rate than main light

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thank you. so you recommend to keep it on as long as the main light is on for the whole period? (do not have sunrise or sunset so no dimming)

I am using it whole period. Sun gives Uva all seasons...and in my latitude even more in vegetative mode...It will help to control internodal distance also. If in veg your main light intensity is lower, try to lower the UVA driving the leds at lower amperage

Budi said:

thank you. so you recommend to keep it on as long as the main light is on for the whole period? (do not have sunrise or sunset so no dimming)

Click to expand...

@Budi
What I have found is too much UV stunts growth and can make things go purple and if not addresed and later comes leaf damage if not stopped plant will die.
This is not a bad thing if you only use UV for a short time when in veg, then when you switch to flower and slowly
dial it up (if you have a way of dimming your UVA ) if not just turn it on a little longer each day.
I have found to much UV to early in your grow will stunt growth and if you put UV on too long at first .
The plant needs time to adjust just like hardening a plant to go out doors.
If you give plant to much UV in a few days you will get leaf damage and if not adjusted major damage could occur.
So less is better till you are pass half way in flower as by then you will have SLOWLY exposed plans to UV in veg,so low power by dimming or turn on less hours per day if you do not have a dimmer for your UV (till flower) and by exposing plants to low doses in veg and early flower are better able to deal with the UV and start increasing THC during flower.
Signs you have exceeded UV dosage plant can take are leaves that seem to droop like they need water, stunted growth, leaf burning or beaching look. If you go slow and give them small amounts then check in a few days if it has had a bad effect as it often it takes days later to see damage to plant so go slow.
I do not know your setup so hard to say how long each day as everyone will have a diffrent size tent and type of UV source.
I have exposed plants to extreme levels of UVA-B and thy are still OK but the growth slowed down so this is a good way to keep stavia's from growing to high but for most grows I suggest lower is better till you get a feel for it
I have about 300 watts of UVA-B in a 5 by 9 foot tent some solocure some are HLG Led
I had all of it on but it was way to much in early flower
so slowly increasing it now using about 80 watts now till late flower then will turn it up a bit till I see it is too much for plant.
Watching your plants carefully is the best way as I think plants can handle far more UV than most feel and suggest to others
To me it is important to slowly allow plants to get used to a small amount of UV when growing,then in flower give them al you have as the plant will be able to handle it more if exposed really caerfully as UV can and will kill plants of your not careful.
I would be intersted in how this grow goes for you.
Good luck!

thank you very much for the help. I ended up using about 26w since i dont have the right driver yet so they are drived pretty soft. main light is about 1400w on 4x8.
I am in middle of the flowering period right now so too late to introduce in veg. my plan now is to start the uv today with 30min and increase by 30min every day.. do you think its a good idea?

Think that considering the low wattage are you using..and the fact that is not uvb , only uva..and also that you are at middle of flowering...you can start using it much more hours ... 26 watts of UVA is very little over a 4x8...