Daily Light Integral (DLI) Calculator

This calculator works out the daily light integral (DLI), the total light plants receive in a day. Enter the photosynthetic photon flux density (PPFD) from your light meter or the light’s chart and the hours the lights are on; you get the DLI in moles per square metre per day.

Formula

DLI = PPFD × hours × 3,600 ÷ 1,000,000. PPFD is in µmol per m² per second; 3,600 turns hours into seconds and 1,000,000 turns µmol into mol.

Worked Example

400 µmol/m²/s for 16 hours.

1. Seconds = 16 × 3,600 = 57,600
2. DLI = 400 × 57,600 ÷ 1,000,000 = 23.04 mol/m²/day

How to read the result

Compare the result with the range recommended for your crop. To reach a target DLI, rearrange: PPFD = DLI × 1,000,000 ÷ (hours × 3,600), or hours = DLI × 1,000,000 ÷ (PPFD × 3,600).

Limits and common mistakes

• PPFD falls off with distance and towards the edges; measure at canopy height in several spots.
• Lux meters do not measure PPFD; conversion factors depend on the light source.

Frequently Asked Questions

What PPFD gives a DLI of 20 over 12 hours?

About 463 µmol/m²/s.

What is a typical outdoor DLI?

Roughly 20-60 mol/m²/day in summer, lower in winter.

Can I use lux?

Only with a conversion factor for your light type.

Does DLI depend on hours?

Yes; longer hours at lower PPFD can give the same DLI.

in ppfd | PPFD | µmol/m²/s | 400 | 0 | 3000
in hrs | Light hours per day | h | 16 | 0 | 24
out dli | Daily light integral | mol/m²/day | ppfd * hrs * 3600 / 1000000 | 2