PPFD for Seedlings, Veg and Flowering (Stage Chart)
Plants want more light as they grow. A seedling scorches under intensity a flowering canopy would soak up. These are the PPFD (µmol/m²/s) and DLI (mol/m²/day) ranges grow-light guides broadly converge on for the three main stages. Sources disagree at the edges, so the numbers below are the span across several published guides rather than one “correct” figure. Every range is sourced.
Target PPFD and DLI by stage
| Stage | Typical PPFD (µmol/m²/s) | Typical DLI (mol/m²/day) |
|---|---|---|
| Seedling / clone | ~100–300 | ~10–15 |
| Vegetative | ~250–600 | ~20–35 |
| Flowering | ~500–1050 | ~30–45 |
The spread is real. For seedlings, some guides keep the first days near 100–150 PPFD at the soil and ramp toward 400–500 as true leaves come in. For flowering, guides split between a conservative ceiling around 600–800 and pushing a strong, healthy canopy past 1000, with the very top of the range usually paired with added CO₂. Aim for the middle of a stage’s band first, then adjust based on how the plant responds.
How to read the chart
- Start low with seedlings and clones. They have small root systems and thin tissue. Too much light stresses them before it helps. Begin near the bottom of the seedling band and raise intensity as the plant fills out.
- Vegetative is the ramp. As the plant builds the frame it will flower on, work up through the veg band. This is where you increase intensity or lower the light.
- Flowering is the peak, within reason. Bud development uses the most light, but the top of the flowering range only pays off with a dense, healthy canopy and often supplemental CO₂. Past the point the plant can use, extra intensity just risks light stress.
PPFD, DLI, and photoperiod
PPFD is instantaneous intensity. DLI is the total light delivered over a day, which is what actually drives growth:
DLI = PPFD × (seconds of light per day) ÷ 1,000,000
That means a lower PPFD over a longer photoperiod can reach the same DLI as a higher PPFD over a shorter one. When you set a target, think in DLI, then choose an intensity and light-hours combination that reaches it. To convert a PPFD reading and photoperiod into DLI, the lux to PPFD converter gets you the PPFD half if you are estimating with a phone.
Measuring your own numbers
If you do not own a quantum sensor, you can approximate PPFD with a phone lux app and a conversion factor. It is rough, but good enough to check which stage band you are in. See how to measure PPFD without a meter for the method and its limits. These stage ranges are guidance, not law. Genetics, CO₂, temperature, and nutrients all shift the optimum, so watch the plant, not just the meter.
Sources
- PPFD and DLI by stage (seedling 100–300, veg 250–600, flower 500–1050): https://growlightmeter.com/lighting-requirements-of-cannabis-over-the-full-grow-cycle/
- Seedling PPFD ramp by week and DLI stage targets: https://www.gorillagrowtent.com/blogs/news/ppfd-for-seedlings
- PPFD for different growth stages: https://www.spider-farmer.com/blog/ppfd-for-different-plant-growth-stages/
- Optimal PPFD for the vegetative stage: https://www.growsensor.co/post/the-optimal-ppfd-for-veg-your-ultimate-guide