Start using DLI

Daily Light Interval (DLI) is a quick and efficient way to calculate how much light our plants are receiving within a 24hr period, allowing for easy light adjustments. DLI will help you and the community to better understand your lighting in a more universal term, leading to clearer communication of what the true light value is.

Almost all smartphones have the ability to use an app (we will get to this don’t jump the gun) in order to calculate DLI, and if that is not an option a cheap LUX meter can be purchased which will allow us to do some conversions in order to obtain a DLI.

However this is not exact science, think of it as more of a way to measure and have a baseline to go from while speaking in a universal language.


Height is A terrible measurement to gauge lighting.

As my hero Bruce Bugbee explains here at marker 5:30, extensive video be warned. Dr. Bugbee shows how lux is not a truly accurate measuring device but without a par meter $$$ it’s the second best we have readily available to us, the First is our specific DLI app (with modification).

The first step to this is getting a LUX meter, they are cheap or free if you download one on your smartphone app store.
take multiple readings from your canopy (ussualy the edges are the most important noting the center will be the strongest), take the average. THIS IS IMPORTANT, YOU NEED AN AVERAGE.

Now put that average lux into a HLG’s lux to PPFD conversion calculator (if you have an HLG) or use one on wave form lighting (first google from LUX to PPFD converter) if you know the type of light your running.

Once you know your PPFD then you can type that into a PPFD to DLI converter. This will give you a number, jot it down so you know where your at.

Now play with the PPFD number in that DLI converter until you get the right DLI for your growth stage

Go back to the LUX to PPFD converter and find out how many LUX you need to get that amount of PPFD to meet your DLI requirements for your stage of growth.

Let’s say it’s 55k lux, okay then in your grow room notes beside your VPD chart (if you don’t have one of these you should it’s another topic though) you should have a couple notes that read something like this.

Veg = 10k lux = 15 DLI
Full power pre stretch = 55k lux =60 DLI
Late flower to avoid fox tails is 45k lux = 45 DLI.
(this is a total made up example)

Thanks to some collaboration, testing, and no expense spared by our members @Bobbydigital & @Hellraiser we now know the easiest and most accurate way to calculate DLI is with a modern smartphone and an app named “Photone”. The trick to ensuring this app is accurate for iPhones involves taking a normal piece of printer paper and laying it over your phone’s camera to work as a light diffuser (not needed on android phones). Set the app on sunlight mode, do not use the LED modes as they are not as accurate from our testing with an apogee meter. Ensure an average reading of the canopy level is taken, remembering the light will be strongest at the center and weaker at the sides.

Now you can dial your lights in very fast with your lux app on your phone and get a good average DLI, which you will want to do weekly until plants stop growing.

This chart is a starting point, play with it. Personally I am still messing with my own setup, while we are hearing that Bruce and his team at Utah state have research showing even clones accept very high light values.
However in late flower high light values can bring out fox tailing.
So personally I like to ramp up to 60 DLI as fast as I can, once I’m in late flower drop down to 45 DLI the second I see a fox tail.
The more powerful your lighting the shorter and busier your plants will be, so depending on your grow style you may want more stretch early on to flill a scog or something. Light spectrum also has an effect on plant morphology with the more red causing again a much wider bushy type plant and blue tall and spread out. I personally love growing plants, giving them a FIM at the 4th/5th node and then letting them flower out after veg (I mostly run autos)
If your in the garden evey day and you enjoy training your plant you may enjoy less light levels Durring veg unlike me.
Here is to plants I hammered with light

Now here is two plants I went a little easier on until post stretch, I really find cranking the light up pre stretch is key to controlling it of course I need more experience with this to say for sure but this is where I’m leaning.

Try not to run your lights to close as this can cause fox tailing as well.

Keep in mind that this is only one part of lighting, which is a very big topic with many variables.


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I appreciate you boss, thanks a lot!!! i’ll be studying all of this after work tonight


Figured I would make a post since it keeps coming up lol, tag anyone you wish, bookmark it etc.


You know I did :wink: thanks again


Been trying to convince my wife I need an Apogee meter, emphasis on “need”.


Yes they are definitely ideal, unfortunately for the average home grower the above post is free and close enough to get an idea of how to gauge things roughly but still have a baseline /# to follow.

I would think any professional grower should have a true extended par meter though, including IR and UV.

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I’ve got an Apogee meter and love it. You can really dial in your lighting that way.

I shoot for 600 PPFD in veg and then up to 1,000 in flowering. I liked Nicky’s comment about light and foxtailing. It will happen at 1,000 PPFD, so I do what Nicky suggesed and turn it down to 700 or so the last 2 to 3 weeks in flowering after the flowers have bulked up nicely.


Thanks Midwest.whats your DLI for your stages?
@Hellraiser has one to.

@merlin44 is using high DLI numbers like myself as well.


Seedlings: 300 PPFD
Veg: 600 PPFD
Flowering 1,000 PPFD
Late flower: 700 PPFD

Sorry, I’ve not calculated DLI, but it would probably be pretty easy by just considering the hours that the lights are on.

It’s a good point. In veg the DLI would be based on 18 hours of lighting and the PPFD (the way I understand it.)


Lol okay that’s half of the info, your DLI?
I run autos so my lights are always on 20hr a day so I aim for the DLI. I will keep in mind your 700 PPFD and maybe try that.
I’ve been using 650 PPFD for 20hr a day in late flower.

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I still get some new calyces late in flower, but I wouldn’t call them big enough to be foxtails. They don’t stack like you sometimes see.


I am interested to see what @merlin44 chimes in because I shoot for that 650 your at 700 so we will see what he says. About fox tailing and late flower.


Okay and LUX app added an average feature so it’s now my preference


@MidwestGuy i couldn’t stand not having a tool that I could use, pulled the trigger.


You will like it. I’m pretty happy with mine.


I usually just blast them with light all the way to the end. I see fox tailing sometimes but don’t worry about it too much.


If you were wondering what was required to get the necessary DLI I used the above chart and math that @Nicky provided I calculated what is needed for a typical 18/6 and 12/12 day.

For a 18/6 day you need a PPFD of 400 (26 DLI), 500 (32), 600 (39), and 700 (45 DLI)

For a 12/12 flip you need a PPFD of 600 (26 DLI), 700 (30), and 800 (35 DLI)

Does that make sense?


It does yes, it shows how hard it can be to get a good DLI with a 12/12 and not great lights.


Nice, Dr Bruce Bugbee talked me into buying one while drinking. I blame him LOL,


Great work - thanks for the useful info. I have looked at the wave form converter. I do not have PPF readings for my light but I have the wavelength graph. I matched it with the closest one on wave form converter.
Current crop was 7 weeks on 12/12 so I turned the photo boost strips down to 40% & raised my lights a couple inches. I can not dim my Kind XL600. The AK-47s I have in there are prone to fox tailing so I tried some preventative measures.