Calculate PPFD and DLI

I just bought a lux meter and watched the video and went through the details here: Start using DLI

However I am stuck at converting my LUX to PPFD and then to DLI. It seems like my math is way off. So right now I am reading 70,000 LUX at the center of the highest point of my plant and about 50,000 LUX on the sides. So I just average it to 60,000 LUX.

When I use the calculator at and just use “Natural Light 6500k” I get some 1380 umol/s/m2. Is that my PPFD? That just seems way off because over 18hrs that would be 89.24 which would kill my plants right?

Is the m2 not being taken into account? My space is a 4x4.

I am not sure if “Natural Light” was the right option in the convertor. I am using the Spider Farmer SF7000 so I am not sure what the relates to in the options or how to turn LUX into PPFD for that.

Also just curious but how do multiple plants in the area effect the DLI and how would you calculate for that? The LUX is going to be the same base on height and intensity.

Any help would be appreciated.

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Do you have a smartphone? If so the photone app is a game changer. Not everyone has one or knows how to use it and when I first wrote the DLI the app wasn’t proven accurate. So it provides both options in there now.

6400k was not the right option, it will be 3000k or 3500k and the readout is the pffd yes.

Multiple plants don’t effect the light output, your simply trying to find a average light reading st canopy level around each plant for each light.


I am really still stuck on this. So I downloaded the smart phone app and even bought the full spectrum light. I created this stupid diffuser that was needed and then checked the PPFD from the top of my plant which is 23 inches from the light. It was reading 1100 PPFD and the light was only at 80% power. At 18 hours a day that is a DLI of about 71 which will kill my plants. I have to be doing something wrong, because I have to turn stuff down?

Using my LUX meter I was getting a reading of about 60,000 LUX. Which based on my light SF7000 should convert to about 1100 PPFD. So if I am not messing up then my readings are right.

However this gives me no room to grow and I have to reduce things. How could I ever run this light at full strength without killing my plants.

So it would seem 1100 PPFD is ok for 12 hours a day bringing the DLI down to about 65. However these are autoflowers. So is their DLI higher? I reading that an average of 1000 umol/s/m2 is common in flowering and can go up to 1500. But at 18 hours a day these are high DLI numbers. How would that even work when I am reading people getting better yields at 20/4 light schedule over 18/6.

you could raise your light higher up or turn the intensity down.

what the 20/4 schedule provides is less opportunity for the plants to stretch.

i’m running 20/4 and about 750-800 canopy ppfd which is just under 60 dli

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Are you measuring across your canopy and averaging? A single measurement under the center of the light won’t give you a proper measurement. You need to test and record your readings across your entire plant canopy and then average all of your readings.


So would center of the light work and then say the four corners. The more numbers you add on the outer edge would bring the average down.

Exactly the reason to get an average. I do a reading every 6” from the outer of the canopy and work my way in 6” and repeat. Kinda like this


Thank you. I have realized part of my problem. I have two plants in my tent so that is really throwing me off. Have to take the plants out of the equation and do measurements to determine the light, height and tent size. So tomorrow I will pull my two plants, mask off a grid on the floor in 6 inch square, probably underneath the protective pad that came with the tent in the bottom. Then build a map at various heights and light percentages. From my most recent read you are trying to get the center around 1000 with keeping all the edges over 500.

So I will raise my light and adjust my intensity to try and get those numbers, a not to high center number but the edges close to over over 500.

Okay first off you didn’t read my tutorial so your getting frustrated. Everything is laid out there.

Your not meant to use the full spectrum light option it’s not as accurate as the sunlight option, so buy the sunlight option if you don’t have it available to you.

Do not take the plants out of the equation, the whole idea is to get an average canopy reading. This means you take a reading at the 4 corners of each plant and the center, then average it and do this for both plants. It will change as your plants grow and you change the height of your lights.

I don’t even do that, I grab my phone and do it manually with rough numbers. It doesn’t need to be exact if you don’t want it to be but at least you’ll know roughly the DLI your getting.

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