What DLI does lettuce need?

12–17 mol/m²/day. Below 10 it stretches; above 20 it tipburns.

How do I measure PPFD without a quantum meter?

Use a smartphone PAR meter app within 20% accuracy, or borrow a real Apogee MQ-500.

DOC №126SEC: LIGHTINGREV: 2026-05-15AUTHORED

PPFD, DLI, and PAR — Hydroponic Lighting Explained

PPFD is light intensity, DLI is daily total, PAR is the wavelength range plants use. This guide turns confusing acronyms into actionable numbers.

BY ROOTLESS FARM

Quick answer

PPFD (μmol/m²/s) measures photons of usable light hitting the canopy per second. DLI (mol/m²/day) is PPFD × photoperiod × 3600 ÷ 1,000,000 — the total light a plant gets per day. PAR (400–700 nm) is the wavelength band plants photosynthesize with.

Targets by crop

Crop	DLI (mol/m²/day)
Lettuce	12–17
Basil	18–22
Tomato (veg)	22–30
Tomato (fruit)	30–40
Strawberry	17–22

Calculate yours

PPFD (μmol/m²/s)Photoperiod (h)

DLI

20.2 mol/m²/day

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FAQ

2 entries

Q01What DLI does lettuce need?: 12–17 mol/m²/day. Below 10 it stretches; above 20 it tipburns.
Q02How do I measure PPFD without a quantum meter?: Use a smartphone PAR meter app within 20% accuracy, or borrow a real Apogee MQ-500.