Trying to understand lighting better

Hi out there I’m new and the more I read the more confused I get on lighting . So I understand I need roughy 100 watts per plant. 40-50 watts sq ft plants takes 2 ft 100watts ? Close to being right? So reading and came across DLI and PPFD and I know these are all different way to measure different parts of light ? So I have 2 lights in 2x2 used app on phone to do DLI it said WAY to much, average PPFD on canopy is around 1000 . How can that be to much when both lights no even at 100% 18 inches away. Btw both lights total watts only 243 watts combined. So not primo lights, Was told with that little watts will not be able to maximize yield but if I’m way over DLI my plants getting all the need plus more ? Very confused, I know u r lighting up space not necessarily a plant, I’m so lost I watched you tubes of the guy from Utah state, and others people had posted still not getting it.

Welcome to the club
I just went with the recommendation of @dbrn32 on an hlg and it’s working out for me

I know it’s good to understand but every time I see anything dli, ppfd, etc it gives me tired head so I burn a bowl and don’t care anymore


Remove this from your line of thinking and it will probably make more sense.

Thanks guys, so with my viparspec xs15000 I get an average 716 PPFD enough to flower all 3 plants according to the DLI thing and only running 18 hrs, I know that can’t be right then why does everyone spend $ on lights when a cheap light can keep your DLI over 60 ? I missing something but what ?

Radiometric energy per square meter pretty much says it all. What it that. Quote from moderator been trying to figure this out. Googled it, read it. I have no idea what this means
diometry is a set of techniques for measuringelectromagnetic radiation, including visible light. Radiometric techniques in optics characterize the distribution of the radiation’s power in space, as opposed to photometric techniques, which characterize the light’s interaction with the human eye

Yep, tired head


agreed, lighting bowl now…


Already been there brother :grinning:


yeah, i had just got to it and reading it…and after the $#t day i’ve had with losing Amy Lee and all the other LIFE things that happened today, i needed NO coercing to light it…lol

Yeah sorry about the hard luck
I think a bowl is well deserved

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Man, i’m not even really THAT mad that i ended up with ONE male. Just that it was THAT plant…the one i’d put THE MOST EFFORT into learning tactics/training on. I think 2 (total) out of 21 plants, being a male, is a pretty darn good ratio for bag seed :wink: . Just pick a “nobody” next time, instead of my “rockstar”…lol


Thanks guys it’s glad to know I’m not the only one scratching my head, no worries deal with it later thanks again

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I thought you had 2 out of 5 or even maybe 3
I didn’t realize it was out of 21 you go brother!

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man, i don’t KNOW what came over me, i had like over 200 blue dream bag seeds (months of purchases, lol) and this one evening back in end of April i got this “brilliant” idea to just drop them all in a glass of water… the next morning, almost ALL, had taproots and the reality sunk in like WADDAFACK did i think i was going to do with 200+ plants??? LOL… i was giving germinated seeds away to friends and neighbors by the dozens :wink: I kept 21 initially of the BDs. Ended up with 7 and only ONE of mine was male and one that i gave a neighbor was male. The rest are all doing awesome as females :slight_smile: My one neighbor i gave one too, his is BUDDING , SO hard right now. Mine are just starting to. Not sure what he gave that thing to make it jumpstart so fast/hard like that but he stands to have a NICE cull from that plant :wink:

EDIT** by the way, if you read or would remember, THIS is the guy who at first, i had woken to getting CUSSED a couple months ago, when he swore my plant turned his male…LOL. Notice he seems to have hushed that fuss up now :wink:

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You might be insane

I decided 2 would be a good number
Oh and hitting the bong right now :grinning:

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Here is my current thinking. Watts = heat non LED lighting. LED lighting Watts=Lumens not wasting energy on heat. My LED bulbs in some of my lighting fixtures are 8 watts but the big Orange Box store where I bought claims, they are equivalent to 40 watt incandescent lighting. So when I hear 40 watts per square foot, 40 watts of what type of lighting? Old non efficient lighting or LED lighting.

New here too, appreciate your patience. So do I need a check up from the neck up to get rid of my stinking thinking. You are a moderator here. I am not challenging you at all. If this was a Golf forum I guess I would compare you to Jack Nicklaus…
School me Jack. I (we) are listening.

Thanks for your expertise


If you just disregard anything saying watts per square foot you will save yourself a lot of headaches lol.

You want the ppf or ppf per watt. Unfortunately, very few places are going to give this to you. In terms of big box store led bulb, there may be some other useful information on the box. Luminous flux or efficacy can probably be converted using online tools if you know the cct and cri. I can tell you the led bulbs I’ve seen reasonably priced are usually similar performance of t5ho. T5ho even at 50 watts/ft² is kinda mediocre. Some of better led bulbs pushing 130 lumens/watt isn’t too bad, but still a long way from latest led tech. The more efficient the led is the less power you’ll need to meet recommended intensity.


Ok I think I had a :bulb:moment, so I on this lighting thing I can see where people would like the bar design cause that is going to give u a better spread of PPHD and fewer hot spots? Example I have a light where in middle I read 1000 PPFD, no plant needs that correct? I have plants on the edges of the light not directly underneath cause that would be to much but with them on the ends of light get a better uniform spread then 1 spot at 1000. Further away from light to plant less PPFD correct, is this where efficiency per dio come in ? If so is this why HLG “do not own” but it’s supposed to be the gold standard why they do not do bar lights cause there light are so efficient. And give a balance spread, if all this is close to correct, why do people care about wattage at all, if it comes down to your PPFD, or DLI for your plant, moderator said throw out the 50 watts and square ft rule, so in theory u could spend 100 on a light for each plant and be fine correct, #### I’m confused again

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Your confused ? You know more than me. At least you had a :bulb:. Last time I had a ha ha moment was when I thought I grow my own. Things do get complicated. I deal with it by taking a break and visiting Frendly Fatties.

Got an email from Bergman. 80/20 rule. Familiar with it. My take on it is you do what your suppose to 80% of the time you will have success. To what degree ? So when it gets complicated I tell myself you just have to score an 80. Still shooting for a 100 but 80 is passing.

Lol :joy: I know right, I have to stop and tell my self this is for fun and hobby. I like the 80/20 thing, ur right just roll with it and see what happens best of luck