Light
PPFD and DLI: What These Light Measurements Actually Tell You
Maxthorne Press · 20 września, 2026
Indoor lighting is often reduced to wattage, but wattage describes electricity consumed rather than the amount of photosynthetically active radiation reaching a leaf. PPFD is more useful because it expresses the photon flux arriving at a surface each second. It is still only a snapshot: the same PPFD delivered for six hours and eighteen hours produces a very different daily dose.
From a momentary reading to a daily dose
DLI combines PPFD with photoperiod. This makes it useful for comparing lighting programmes, but not for declaring one universal optimum. Plant species, developmental stage, leaf temperature, carbon-dioxide availability and root-zone health all affect how much light can be used productively.
Measure the canopy, not the marketing claim
A lamp specification describes performance under stated test conditions. The plant experiences the distribution inside the actual space. Take several measurements across the canopy, note the distance and dimmer setting, and look for uneven hotspots. The aim is not the highest number; it is a stable light environment the whole system can support.