Beginner questions - How do you calculate lighting requirements?

[Inactive account]

As I've been putting my little Growers buddy toolkit, I've been thinking about common questions that pop up within the community. One question that seems to pop up all the time is how to positition your lights or how close should my light be etc. Its something I struggled with when moving over to LED and I've fried my fair share of plants. But, its fairly straight forward once you know how and have a few things in place.

First, you're going to need a par meter. If you don't have £400 to burn and have an android phone, head over to here and grab that app. If you're an IPhone user, get a better phone :) Or borrow someone's.

Next, lets establish some baselines. You're going to have to trust me a little on this one :) I did ask ChatGPT and it agreed with me, but you can do your own research and play with the numbers if you like. These figures are just guidelines.

Seedlings: young plants: 10 - 20 DLI
Vegative: 20 - 40DLI
Productive: 40 - 60DLI * 60 if everything is optimal and your CO2 levels are high enough. I'd stick to 45 for beginners. Then push if you feel like you can.

OK, we have a par meter and we have our baseline figures, let's do some simple math. We can calculate the required PPFD by picking a target DLI and runtime (how long your lights are on for). The plugging in those variabels to this simple equation.

PPFD = DLI / (RUNTIME * (9/2500))

Cool, so, let's run through a practical example. We have some seedlings that have just germinated, we know from our chart that seedlings sit between the 10-20DLI range. Since they're just out of the ground, let's go for the lower limit. We're going to be running our lights for 18/6.

10 / (18 * (9/2500)) = ~154PPFD. Awesome, so you now know that those seedlings require 154PPFD and you can set your light to suit. If you don't have a dimmer, you will have to adjust the height of the lamps to match, if you do have a dimmer, rule of thumb for LEDs is ~60cm from the canopy and HID ~1meter.

Grab your phone, open the app and adjust the wattage or height until you achieve the desired PPFD.

Remember, these are all just guidelines, if you have a fussy plant or you have the ultimate commercial cropper that can gobble up 60+PPFD, go for it. All cultivars are slightly different. This little guide works great for me though and takes the guess work out of the equation. And saves you from frying plants like I did ...... lots of times *welp*

Happy growing!

[Treetrunk]

Good stuff.
Downloaded the app. I'll have a play

[seymore_budz]

Enjoy @Treetrunk I splashed out on a PAR meter a while ago. Wasn't cheap, but I do love a gadget.

BTW, to do the inverse and calculate DLI from ppfd and time, you can use the following.

DLI = PPFD * RUNTIME * (9/2500)

You can also check your figures here.

https://www.omnicalculator.com/biology/ ... tegral-dli

[Wrh]

Will definitely be downloading that app thanks for the info seymore, not just this either the nutrient stuff is great too

[Dex]

Got da app man, thanks @seymore_budz and same as Wrh thanks on the nutrients...

Thanks amigo