What does PPFD really mean

I have three 600w LED lights that have an average PPFD of 390umols each that I use for flowering. They draw 820 watts for all three. I can’t find out if this number is ok or not searching online. @dbrn32 I think you might be able to “shed light” :grin: on this for us.


Photosynthetic photon flux density. It’s expressed as umols per second per square meter. To get ppfd you need to know the total amount of photosynthetic photon flux a light produces, which generally takes a radiometric sphere to measure. Then apply it to an area.

I’m pretty sure we found a third party sphere test of @Bogleg’s cobs, but I don’t remember what his Ppf was at his operating current. Can you help me out? If he remembers we should be able to calculate based on amount of cobs and size of his tent.

Where are you getting the data from on your lights? I’ve seen a few of the budget lights advertise their ppfd as a spot measurement directly below the lamp, and while those are useful numbers it’s not exactly what ppfd is.

@dbrn32 It’s on the spec sheet for the light.
I did read somewhere that it may not really mean much because most of the light manufacturers don’t test it correctly. Sorry for the crappy picture. I have the file as a PDF but I can’t upload a better image unless it’s a jpg type, so I had to use the camera.

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I can read it. That number sounds realistic for 300 Watts from the wall in that style of light.

So what they’re giving you is ppf, so in a 1mx1m tent your ppfd would be 390. If it’s .5 square meter tent your ppfd would be 780 umols per second per meter squared.

Make better sense now?


I still don’t understand if the ppf number is decent for my light. I have three lights covering an area about 1.5m x 1.75m. (4’ x 5’)
I know it’s fine for veg, but not sure if it’s going to be enough for flower.

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Ppf of 390x3= ppf total of 1170.

20 square feet is equal to 1.858 sq meters. So 1170/1.858= Ppfd of about 630 umols s/m2.

Target ppfd for flowering is generally between 600-1000 umols s/m2. So you’re just sneaking into that range. Some consideration should always be taken for the fact that you’re providing it from three separate light sources too. Which is better than providing it from a single light source in terms of balanced canopy levels, but not as good as providing it from 4 light sources.

When I build a light for myself, I try to figure it to be in the 800-1000 umol s/m2 range with the ability to dim to some extent. I haven’t always been able to find ppf data, but you can make some reasonable assumptions based on manufacturer supplied data. If I can get ppf of a different led, and then say that light spectrum is similar, you can make the assumption that par values will be in line with the differences in efficiency, luminous efficacy, and power levels between the known led and led i’m Trying to find data for.

For example, if I know the ppf of a specified bin cxb 3590, and I want to compare it to 2 bins higher in the same color temp, you can expect the increase in par to be somewhere between 50-100% of the increase of efficiency or luminous efficacy increase from one to the next. It becomes harder to do that when going between two different manufacturers, different color temps, or different cri levels obviously. But that’s when I go on the search for some more closely related data.


For the gen 5 Citizen CLU048-1212 I have the lumens per watt running at 40% is 128 and the ppf is 82 umol/s. I have 15 of those in my 4x4.


Thank you for the help on the ppf and ppfd. Sounds like low ppf means low yield. looks like I’m going to have to drag out the Frankenstein test fixture I made with the driverless pink cobs to get enough light for a decent yield. When my Golden retrievers have pups this summer, I’m going to be able to buy good cobs. I’ve gathered enough materials from reading your DIY thread to build the frame and it shouldn’t need active cooling. All I need is the COBs and drivers. Again, thanks for the explanation @dbrn32.


So works out to be a ppfd of about 850 umols s/m2 correct? Which is right around the point of diminishing returns according to many. Not a coincidence either :wink:

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No problem partner. Active cooling isn’t a terrible thing. I just try to avoid it if possible.

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Whenever I read these lighting questions and answers - my brain starts to melt. I am a complete beginner and just put my plants in a 3x3x6 tent. I wanted to go with LEDs so I bought the Viparspectra 450w. All of my babies seem to be thriving with only the veg switch on at 24" from plants. From all my research that seemed a decent light for vegging my plants. I am also trying to keep some of these initial costs at a minimum while I learn. As I am aiming for a perpetual grow cycle, I plan to purchase a 3x3x80" tent for flowering and thought the general formula was to double my lighting. Any thoughts on the lights for the flower tent would be appreciated as you @dbrn32 seem to be to lighting go to guy. Thanks, Jeb

You have a very good light for vegging your plants in that size space. And you’re not far off from your thinking either.

When you’re running separate spaces for veg and flower, the ideal thing to do is tailor your lights to their specific job. If there was a downside of the vipsrspectra lights, it would be their flowering spectrum. Even with the bloom switch on, there just isn’t a lot of red diodes on the light. So while you could put two of those models in a flowering tent and do pretty good, there are options out there that are still pretty versatile but more geared to a flowering spectrum.

The biggest thing that usually keeps people back from lighting is the price. Depending on what your budget is, could open up quite a few different options. Right now in a 3x3 for flowering, I think we’d be pretty hard pressed to find a better option than the 2 board quantum board kits that @MattyBear and @Kcdaniels are using. You can save a few bucks and assemble them yourself with a screwdriver and set of wire strippers. Or, buy them assembled if growerslights has them in stock. They are proving to be very effective in that size space, offering very good par levels for minimum power consumption. I would highly suggest checking them out first, and then comparing from there.


Thanks @dbrn32 I will check that out. If the plants went under the Viparspectra 5 days ago and seem to be growing nicely when would you add the Bloom switch (33 days in soil from seed today)? I plan to have the flower tent and new light set up on February 24th. Budget for flower lights $300-400. I will tag you in my grow if I haven’t already.

You can add it any time really. You may want to keep an eye on heights after you add the bloom switch as it’s more power. But I wouldn’t assume you have many issues at that height with plants that are plenty mature. The other side of that is, if you’re seeing desired amount of growth, you could always just keep them on the veg switch and save a little energy too. Entirely up to you.

Here is the specific model I was talking about. You would want them in 3000k color temp. Looks like even paying for assembly they come within the price range you were hoping to be. That’s a reasonable budget, so if you’d like some other options let me know.