dli Micro moles and small spaces

[Crow River]

I've been doing a fair bit of reading on lighting for cannabis, as I was concerned my plants were not getting sufficient light.

 

There are a lot of resources out there, but most are dealing with photoperiod plants, very few cater to autoflowering varieties, which are not flipped but stay on 18/6, 20/4 or even 24/0 throughout.

 

Also most information assumes a tent like setup of at least 4 sq. feet, with lights hung between 18 and 36 inches away from the canopy. I'm growing in a small cabinet, the floor area is approximately 3 sq. feet (0.28 sq. metres), and the distance from the top of the pots to the lights is only around 22 inches (55 to 56cm approx.). 

 

As a result I'm finding it tricky to estimate what the optimum PPFD for my plants should be. I've been using an Android app to take measurements, but depending upon which LED profile preset I use, I get different results. 

 

So I'm still not clear if I have the right light intensity for my small space.

 

If anyone with more knowledge could advise, that would really help. Some data below.

 

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Autoflower plants, currently entering week 3 of flower.

 

20/4 light schedule.

 

Main lights: 2 x 60w LED panels, "blurple" (percentage is 74/26 red/blue) with smaller numbers of white, orange, UV and IR LEDs also.

 

PPFD readings at the canopy are 570 umol/s/m2 using the red/blue preset, 286 umol/s/m2 using red/blue/white preset.

Lux reading is 5600 approx. at the canopy.

 

Side lights: 2 x 18w daylight 6500K LED wall panels, with 36 white LEDs each.

 

PPFD readings at the nearest plant are around 56 umol/s/m2 using Low CRI LED 6500K preset. They are rated at 1500 lumens each, and the lux readings are roughly in line with this close to the lights.

 

Total wattage at the wall is 156w, which gives a an estimate of 52w per sq. foot, or 557w per square metre. As I'm using side lighting there might be some variation there.

 

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Edited April 26, 2021 by Crow River

[Arthur Mix]

Have you actually grown before with this set up? Getting light readings from blurple lights is very hard to do tbh even with the equations to work it out .

[Crow River]

@Arthur Mix No I haven't, this is my first grow. 

 

The plants seem a bit stretchy, but that might be down to two factors: I had them on the window sill from seed to 26 days; and until two days ago my lights were I think underpowered as I had just one 60w main grow lamp, plus the 36w of side lights.

 

I've read elsewhere that it can be difficult to measure blurple light output. Maybe the PPFD is somewhere in-between the two readings I took? Of course a mobile phone app might not be very accurate either...

Edited April 26, 2021 by Crow River

[MindSoup]

Unfortunately as said above with a blurple its not really possible to be accurate without spending a lot of money on a sensor (waaaaay more than a really really good light) as you say the phone apps are pretty useless, although migro did find a good one for Android and made a handy chart to convert its readings to accurate ones by comparing it to a proper sensor, at different spectrums, not blurple or 6500k though. TBH your best bet is probably to just chuck it all in the bin and start again, but now u have it, just see how you get on this run and start saving and researching for an upgrade. Short height spaces are tricky, as your canopy rises you get less and less even coverage, so something that covers the most amount of your ceiling possible is best, a lot of success has been made with normal household 3000k/35000k led bulbs (migro has a guide on that too). 

 

I've just bought some little 3000k 9v "Dimmable Recessed LED Panel Lamp" jobbies off ebay to play with as my light isn't wide enough to catch the edges of my canopy. I'm hoping they will do a good job, but I'm sort of winging it, from what I can tell they're more or less the same as the ones migro uses just a different shape/ wattage. They're crazy cheap so figured I'd have a try. Keep an eye on my diary for more info, probably next week some time. 

 

 

Edited April 26, 2021 by MindSoup

[Crow River]

@MindSoup That sounds like an interesting project. 

 

Yeah I made quite a few rookie errors on this grow. It was a rush to get the cabinet built before my plants grew too much... They're still alive and look as though they'll produce something, so not a disaster yet.

 

If I look at advice regarding "rule of thumb" on cheaper less efficient LED grow lights, it would appear I'm in the right sort of zone regarding watts per sq. foot/metre. However given the other mistakes made on this grow, the end results won't be purely down to whether the lights are working well or not.

 

I'll probably persevere with the blurples (well they have some extra different spectrum LEDs so not pure red/blue) and my repurposed wall lights, but will run them from seedling stage on a single plant, start LST early, etc. See what happens.