DLI stands for Daily Light intake. This is the total amount of light photons that a plant receives per 24 hour period. Usually, we measure these light photons from within the PAR range which is approx 400-700NM.

How Do we Measure DLI

The easiest way to measure DLI is to take a light measurement the plant will receives per second (PPFD). We then multiply this measurement until we can calculate the total light photons that the plant receives per 24 hour period.

What does PPFD mean?

PPFD is the amount of light photons that plants receive per second within the 400-700nm spectrum within a metre grow space.

What is the formula to Calculate DLI?

DLI can be calculated if you know the PPFD per second (µmol m^-2 s^-1) average in your grow space.

PPFD (light per second) x 60 Seconds(light per minute) x 60minutes (light per hour) x Photoperiod (amount of hours lights are on)

Example of 1000PPFD for 12 hours:

1000µmol m^-2 s^-1 x 60 x 60 x 12 = 43,200,000 µmol m^-2 s^-1 or

1000µmol x 12 hours = 43.2 moles per square meter per day

1000µmol x 18 hours = 64.8 moles per square meter per day

Why is DLI Important?

The amount of light that a plant is exposed to over it’s lifetime is one of the major influences in indoor growing. Optimum light levels increase the transpiration rate of the plant which creates more growth and more demand for nutrients. This means Getting DLI right will help improve flower yield and fruit yield.

Minimum DLI Needed to maximise flower yield

PPFD of 500µmol m^-2 s^-1 is the minimum amount of light needed for flowering plants.

This is 21.6 moles per square metre per day.

Because the photoperiod of flowering plants is shorter (usually 12 hours), It is a good idea to use powerful lights for the flowering phase of growth.

The Best DLI for maximum flower production

PPFD of 1300µmol m^-2 s^-1 is generally considered the best amount of light for maximum flower production.

This is 56.16 moles per square metre per day.

To increase above 43.2 moles per square meter per day will increase the plant’s need for Co2 and supplemental Co2 may be required.

What Happens if I give my plants too much light?

You will need to add extra Co2 to your grow room.