LIGHT SCIENCE: Day Light Interval… Simply Explained
Day Light Interval
Day Light Interval (DLI) is the cumulative amount of light energy for a given area over a one-day period, expressed in moles per meter squared per day (mol/m2/day). In general, increasing light photons over a day period increases photosynthesis thereby enhancing growth, increasing quality and improving yields. DLI reaches a saturation point, varying by plant type (see attached graph). This saturation point (Pnmaxx) basically means that applying any additional light over the same day period will have no additional positive effects on maximizing photosynthesis.
How do I translate my light meter measurements from µmol/m2/sec to a DLI value? Suppose we read an average of 350 µmol/m2/sec from our light meter and are operating our lights for 12 hours/day . . . . . the resulting equation to calculate DLI would look as follows:
350 µmol/m2/sec * (1 mol / 1,000,000 µmol) * (12 hours / day) * (3,600 seconds / hour)
The resulting DLI is 15.12 mol/ m2/day
DLI recommendations for cannabis vary significantly, depending the source but are typically between 15 and 25. Growers understanding the maximum DLI requirements for their specific plants will be much more apt to maximize yield while minimizing the energy costs related to lighting.