LED-lighting for 4x8 tent?

3 years ago I was growing in a 1000x1000cm (3x3 feet) tent with 8 CXB3590 3500K Cob´s at 1750 milliamperes each. A total of 492 watts, and 45.7 W/sqf.

I have been reading up, and strip-builds and "quantum boards" seem to be what people are using now. Most prebuilt lamps seem to be using white leds with a dash of far red.

My plan is to use 3500K color temperature lm301b´s with no added far red or UV. A strip build is out of the question where I live, as aluminium profiles are expensive and hard to source, so I will be getting QB288, heatsinks and drivers from China(most likely kingbrite)

I am aiming for 1000-1300 ppfd. With my cob build, I feel that there was room for more light, and I could definitely have pushed harder than 46 W/sqf. I live in a city, so CO2 levels are elevated and I will be cohabiting with this tent.

I watched a Migro video where he tested a HLG QB288 6 board build in a 4x4 tent where the custom rig consumed 720W and provided ~ 1000 ppfd to the canopy. Im thinking of increasing the board count to provide better uniformity and made a couple of drawings in sketchup of a 4x8 feet or 2.4x1.2 meter tent. The tent and heatsinks in the drawing are made to scale.



This is probably overkill and I will probably have to dim the QBs in the middle down to get to 1000 ppfd. But raising such a lamp higher should cause more scattering of light hitting the plants at more angles. Of course reducing gpw in the process.



This 24 board build should produce excellent canopy spread and I could maybe get closer to the canopy so gpw would be increased. 1440W is probably overkill, but this gives me flexibility in raising the light to get even more scattered light into the canopy.

Feedback would be appreciated. I have been thinking of going for a 18 board build with 80W pr board(1600W total) Does anyone have any experience with the kingbrite heatsinks? Are they suited for running 80 watts efficiently?

80w a board wouldn't need much of a heatsink anyway.
Many strips don't require more than standard U channel Aluminium either.

You will get better eyes on your question in the LED section, but I will give a couple of people who spring to mind a shout out.

@Rocket Soul @Moflow

Ive not trried their heatsinks but they are rated for 120w. I think 80w would defo be safe. Especially with air moving over cannopy and the lights.

But yeah, its over kill. Youll end up running them on 60w i believe. Is this a tent or room? How do you plan on hanging all this?

You can also have a look at @bigmikey86 build, he runs 6qbs on 3x240s in 4x4. I dont think he ever maxes it out.

@Rocket Soul

This will be in a tent. I will make two 4 x 4 frames from aluminium L-profiles that will hold the quantum boards into position.

The plan is to use one HLG-240H-48B pr. 4 boards. 6 such drivers and a total of 24 quantum boards. At full throttle they will process 1440 watts of power. Most likely I will not need more than this. But I have seen growers on youtube using much more power pr sqf. And some people over at the ledgrower forum believes that 50 watts/sqf is a overall good level, even without CO2 enrichment.

When I asked for advise on building my first CXB3590 Cob fixture back in 2016, everyone seemed to agree that 400 watts of power would be ideal for a 3x3. But I bumped it up to 492 watts because my gut told me more is better. And my results were good. I yielded about 1.3 gpw on my second grow from clones. And the plants loved the light. I could probably have increased the power to 550 watts in that 3x3.

But I understand that quantum board efficiency is quite a lot better than cobs. My cree cobs are about 157 lumens/watt driven at 1750ma. QB288´s should output about 190 lumens/watt at 60 watt

Thank you for linking that 720 watt 4x4 build. I will definitely have a look at it.

NapoleonBlownapart said:

@Rocket Soul

This will be in a tent. I will make two 4 x 4 frames from aluminium L-profiles that will hold the quantum boards into position.

The plan is to use one HLG-240H-48B pr. 4 boards. 6 such drivers and a total of 24 quantum boards. At full throttle they will process 1440 watts of power. Most likely I will not need more than this. But I have seen growers on youtube using much more power pr sqf. And some people over at the ledgrower forum believes that 50 watts/sqf is a overall good level, even without CO2 enrichment.

When I asked for advise on building my first CXB3590 Cob fixture back in 2016, everyone seemed to agree that 400 watts of power would be ideal for a 3x3. But I bumped it up to 492 watts because my gut told me more is better. And my results were good. I yielded about 1.3 gpw on my second grow from clones. And the plants loved the light. I could probably have increased the power to 550 watts in that 3x3.

But I understand that quantum board efficiency is quite a lot better than cobs. My cree cobs are about 157 lumens/watt driven at 1750ma. QB288´s should output about 190 lumens/watt at 60 watt

Thank you for linking that 720 watt 4x4 build. I will definitely have a look at it.

Click to expand...

First, use AB drivers, or even A drivers. B is problematic with voltage.

Also use t-profile instead o L.its.more.sturdy

@NapoleonBlownapart as rocket said, I can’t even dream of getting close to maxing out. Maybe with CO2 but that’s not how I grow due to a 24/7 vented tent. On my second run with it and I tried getting it above 530w but the plants said “uh uh”. So far I’ve found it’s super easy to maintain 80-85f with the three drivers and boards running at lower wattages. The comfy mark seems to be 18-24”, outer boards at 140-180w/ pair, inner pair of boards at 100-140w. I like to start at 380w and ramp up within the first 2-3 weeks then keep it at a steady 500w there on out.