Grow Like Pro

reference · Intermediate

PPFD, DLI, and photoperiod explained

Connect instantaneous light measurement with the light a plant receives each day.

By Grow Like Pro Editorial Team · Published · Updated · 1 min read

Botanical illustration of a healthy plant
Editorial botanical illustration.

Key takeaways

  • PPFD is an instantaneous photon flux measurement.
  • DLI combines PPFD and duration.
  • Uniformity and crop response matter alongside averages.
On this page

Separate rate from daily total

Photosynthetic photon flux density describes photons reaching a square metre each second. Daily light integral accumulates those photons across the photoperiod. For a constant PPFD, DLI can be estimated as PPFD × light-hours × 0.0036.

Measure the canopy

Take readings across the crop at canopy height rather than relying only on a fixture’s centre value. Map bright and dim areas, because a good average can hide poor uniformity.

Adjust carefully

Crop, cultivar, carbon dioxide, temperature, age, and acclimation affect useful intensity. Increase light in steps while watching leaf temperature, colour, posture, and growth.

Sources

  1. University of Minnesota Extension: Small-scale hydroponics
  2. Oklahoma State University Extension: Electrical Conductivity and pH Guide