Cannabis DLI info

Cannabis DLI

The daily light integral (DLI) is the total sum of photosynthetic lighting intensity measured as PPFD over a 24 hour period. In short, the DLI is a measure of usable light your plant receives over a day. Ultimately, supplying adequate light intensity and duration (i.e. the DLI) is the single most important factor when it comes to plant lighting. 

The important part about plant lighting is that each plant has a maximum DLI in its respective growth stage. Thus, the DLI serves as a measurement that provides cultivators insight into the amount of usable light that a crop needs to flourish. Luckily, the effects of DLI on plants is well researched for many plants and we can harness this knowledge to cultivate cannabis better and cheaper.

What is the formula you use to calculate day light integral DLI in moles?

Multiply the PPFD(photosynthetic photon flux density) by the daily light hours; Multiply the result by 3600; Divide the result from step 2 by 1000000; and. The result is the DLI value as mol/m²/day

This upper limit ranges broadly for different crops. Lettuce is 15-20, Tomatoes is 35-40, and pretty much all other crops are in between.

That is, except for cannabis. Cannabis is unique for commercial cultivars in that it will have a uniform increase in yield proportional to DLI right up to 45 DLI, with many strains going as high as 50 DLI or more. This is easy to understand since most original cannabis strains evolved in equatorial mountains with very high natural light levels. Below 40 DLI, cannabis will start to see subtle changes in flower structure and resonation as well as the proportional decrease in yield.

So, 40-50 DLI is the sweet spot for flowering cannabis, and this is supported by the fact that a 1000w HPS over a 4×4 tray typically delivers around 40-45 DLI over 12 hours. Optimum Veg DLI levels should be a minimum of 75% of flower DLI to avoid shock when moving from veg to flower.

Cannabis PPFD Range

Growth Phase PAR Level (PPFD)

Seedling / Clone 100 – 300

Vegetative 250 – 600

Bloom / Flowering 500 – 1050

Cannabis Photoperiod Range

Growth Phase Photoperiod (h)

Seedling / Clone 16 – 24

Vegetative 16 – 24

Bloom / Flowering 10 – 13

Maturing 10 – 14

Increasing Yields with CO2

Remeber higher light levles will benifit from CO2. General indoor CO2 levels of about 400 to 600 ppm quickly restrict photosynthetic activity to less than half of what would be possible. Supplementing higher CO2 to at least 800 ppm greatly boosts photosynthetic activity and allows for more light or rather higher PAR levels. If you really want to max out your cannabis plant’s growth, we recommend the following CO2 levels:

Growth Phase CO2 Level (ppm)

Seedling / Clone 400

Vegetative 400 – 800

Bloom / Flowering 800 – 1400