How much light do your cuttings get in a day?
Daily light integral (DLI) is the total usable light your cuttings or seedlings get in one day. If you know PPFD at the leaf (from a meter or a manufacturer chart) and how many hours the lamp runs, this tool does the math.
DLI = PPFD × hours × 0.0036. Enter PPFD in µmol·m⁻²·s⁻¹. The answer is in mol·m⁻²·d⁻¹. Example from Virginia Tech: 200 µmol·m⁻²·s⁻¹ for 16 hours is about 12 mol·m⁻²·d⁻¹.
Enter PPFD and hours to see your daily light integral.
What the number means
Compare your result to these extension ranges:
- Virginia Tech (SPES-720): about 5 to 10 mol·m⁻²·d⁻¹ for seedlings and for cuttings.
- Iowa State medium: 6 to 10 mol·m⁻²·d⁻¹ for vegetative cuttings (and for starting seedlings on the high side of that band).
- Iowa State high: 12 to 16 mol·m⁻²·d⁻¹, with some seedling starts on the low side of that band.
These are published bands for crop examples, not a single perfect number for every jar.
How far to hang the light
PPFD falls off as you raise the fixture. Fluorescent and LED distance notes from Iowa State, plus tighter seedling gaps from UMN, Clemson, and Wisconsin, are on best grow lights for indoor propagation. Use that page for inches. Use this tool once you have a PPFD reading.