Research methods · MTH-LGT-001

Light, spectrum and DLI

Spectral composition, PPFD, DLI, photoperiod, plant position and the distinction between electrical power and photon exposure.

Markdown JSONRevised 2026-07-26

In brief

Spectral composition, PPFD, DLI, photoperiod, plant position and the distinction between electrical power and photon exposure.

Central lighting and imaging module integrated into the FlavoRotor system — **Central optical module.**Original v2.0 design image. Plant-level photon exposure must be established by a measured PPFD and spectral map.

Required metrics

Metric	Definition
Spectrum	photon distribution by wavelength at plant position
PPFD	instantaneous 400–700 nm photon flux density
DLI	daily integrated photosynthetic photon exposure
Photoperiod	scheduled light duration
Uniformity	spatial distribution across plant positions
Leaf temperature	thermal outcome at the tissue, not only room temperature

L-1

\mathrm{DLI}=\frac{1}{10^6}\int_{0}^{86400}\mathrm{PPFD}(t)\,\mathrm{d}t

\mathrm{DLI}

\mathrm{mol\,m^{-2}\,d^{-1}}

for constant

\mathrm{PPFD}

and photoperiod

t_h

in hours.

ExplanationDaily light is the time integral of photon flux at plant position. For constant PPFD, this reduces to PPFD multiplied by photoperiod in seconds, divided by one million.

Published basil study

In hydroponic Italian Large Leaf basil, controlled supplemental-light spectra altered key aroma volatiles under a defined experimental environment. The transferable conclusion is that spectrum is a valid treatment variable. The exact result requires matching cultivar, DLI and other conditions.

Why wattage is insufficient

A 50 W electrical rating and manufacturer efficacy estimate cannot define PPFD inside a cylindrical system. Optical distribution, distance, angle, reflection, obstruction, thermal state and plant position must be measured.

Article bibliography

Required metrics

Published basil study

Why wattage is insufficient

Sources used on this page