Morning everyone, hope your weekend is going well for you.
My question is how much light is needed in a 4x4 tent? Im trying to tune in my grow and was wondering if I’m using enough light in my space. I’ve read others talk about 30w sq/ft is needed to produce decent bud, is this correct?
Currently I have 2 cob lights each pulling 112w actual from the wall and a 250w quantum board for a total of 496w combined.
So if this is correct 30w x16sq/ft=480w needed, and I have 496w combined, am I covered then or have I totally missed the mark and dont understand.
I just harvested a couple weeks ago and the weight wet was 549gr then dry was 112gr dry, so it works out roughly to .5gr/w and most I think go for 1gr/w as a target, am I wrong? This grow only had the 2 cobs going, the quantum board was added 2 weeks before harvest so doesn’t really count.
If someone has a moment to educate me on lighting and intensity I’d greatly appreciate it.
Thank you and happy growing.
Well 30W/m2 is on the low end for LED, but adding more light probably isn’t going to change your grams per watt… but there’s a dozen factors that influence your yield, not just light. Genetics, how you grow and how well you cater to your plants needs, density of your canopy, evenness of your canopy, temperature and humidity… just lots of other environmental factors involved as well.
But in general, if you just want to get more yield, I’d say you could add about 10W/sqft more and all other things equal, you can still probably get a 20-30% increase. Anything above that probably gets into diminishing returns without supplementing CO2.
Everything Lefty said, plus one thing. Gram per watt was the mark to hit for HIDs. LEDs being more efficient means gram per watt should be easier to achieve than before.
Lefthandseeds thank you for your input. That gives me some targets to hit. This was my first ever seed to harvest and was happy with our outcome, totally know I’ve room to Improve, little mistakes here and there.
Yield is not our goal, if it happens great but I’d rather quality and taste than quantity. So that being said what light is needed for a 4x4 space?
Again thank you for your advice I appreciate any pearls of wisdom
If you struggle with high temperature in your tent, then adding more light will probably not help quality. High temps will boil off terpenes faster, and really high temps will do that even more plus it will cause your plants to struggle by being too far out of the good VPD zone. But if your temperatures are fine or even a little low, then you might also benefit from the added power elevating the temperature a bit.
For LED, I try to shoot for 40W/sqft. In some spaces I’ve had up to 50, but always end up dimming them down. I’d recommend getting a decent LUX meter from amazon (not a phone app, because they don’t properly dim the CCD from the light intensity and can’t measure high end intensity well). Then set your canopy around 40-50k lux by adjusting the height. If you have to get your lights less than 12" then you definitely need more light. It’s better to have more light farther away, because that means you’ll have more even intensity at the canopy.
What you have shared I do to an extent. Unfortunately I have been using my phone and a downloaded lux meter not app, not sure if that matters but like you I’ve been trying to be at that 45-60000 zone which has been putting my lights at the 24-30" above the canopy during veg then I slowly moved them down during flowering and settled at 18" above at the end. I wasn’t seeing light burn at that height but maybe I wasn’t helping either. That was mostly with the 2 cob lights, for cheap Amazon lights I was impressed what they did but maybe 1.5x1.5 at best each thus why I added the quantum board, but it was purchased towards the end of that grow, so I don’t have a full grow yet with the new addition. But with what you’ve mentioned I seem to be in the ballpark just need to dial my grow in now
I run 37.5 watts of LED per sq/ft at 12-14” away from the canopy and have good results
I’ve got some docs about how cannabis responds to light under various situations, with CO2, without, higher temps, lower temps, that kind of thing. It may have some helpful info for you. 
Light dependence of photosynthesis and water vapor on Cannabis.pdf (862.8 KB)
Temperature response of photosynthesis in different varieties of Cannabis.pdf (1.4 MB)
was this after de-seeding or before? if it’s AFTER then no sweat at all-- remember making those seeds takes extra energy & resources & the plant favors the seedmaking, AFAIK.
There is a couple of good sites. Growweedeasy.com and cocoforcannabis.com check the light sections. They are easy to navigate.
Cannabissequoia it was more a question of if I’m giving the plants enough decent light for full grows. No point in doing things half assed and since I have nothing to compare to or with I rely on other members advice for a starting point until I can establish my own. Eventually I’ll get into breeding and what not but for now I’m happy to get some successful harvests under my belt
Wasn’t @Mr.Sparkle only running like 20-25w/sq ft? I remember something about light toxicity at around 30-35. LED seems to be a bit more subjective, and source makes a difference of course. There’s such a wide range of LEDs out there that I would think it depends. Older, less efficient, diodes would require more, newer diodes less.