Light Schedule Planner
BetaCalculate your Daily Light Integral (DLI), PPFD, and optimal light schedule based on your setup and growth phase.
BetaThese tools are built from our own experience and deep research. We're actively testing and improving them in real conditions. Got feedback or ideas to make them even better? We'd love to hear from you!
DLI Too High
Target: 25–45 mol/m²/day
Your plants may experience light stress. Consider raising the light, dimming if possible, or increasing the grow area. Watch for bleaching or curling of upper leaves.
PPFD
1000µmol/m²/s
DLI
64.8mol/m²/d
Light Hours
18h / 6h
Watts/m²
400W/m²
Schedule
06:00-00:00
PAR Efficiency
2.5µmol/J
Understanding Light Schedules and DLI for Cannabis
Light is the primary energy source for cannabis growth. The amount and duration of light directly impacts plant development, yield, and potency. Understanding DLI (Daily Light Integral) helps you optimize your lighting for maximum results.
DLI measures the total amount of photosynthetically active radiation (PAR) received by your plants over a 24-hour period. It's measured in mol/m²/day. For cannabis, seedlings need 12–25, vegetative plants need 25–45, and flowering plants need 35–65 mol/m²/day.
PPFD (Photosynthetic Photon Flux Density) measures the light intensity at your plant canopy, while DLI accounts for both intensity and duration. A lower PPFD over more hours can achieve the same DLI as a higher PPFD over fewer hours.
Light height significantly affects intensity. Moving your light from 40cm to 60cm above the canopy reduces intensity by roughly 40%. Use our calculator to find the sweet spot between coverage and intensity for your specific setup.
Frequently Asked Questions About Light Schedules
Most growers use 18 hours on / 6 hours off for vegetative growth.
Some use 20/4 or even 24/0, but 18/6 provides a good balance of growth and energy savings while giving plants a rest period.
DLI (Daily Light Integral) is the total amount of photosynthetically active light your plants receive in 24 hours, measured in mol/m²/day.
It's the most accurate way to ensure your plants get enough light, accounting for both intensity and duration.
It depends on the light type and wattage.
As a starting point, LEDs typically hang 30–50cm above the canopy.
Too close causes light burn, too far reduces intensity.
Use our calculator to check your PPFD at different heights.
LEDs are more energy-efficient (2.0–3.0 µmol/J vs 1.5–1.8 for HPS), produce less heat, and last longer.
However, HPS lights are cheaper upfront and some growers prefer the spectrum.
For most setups, LED is the better long-term investment.
Yes.
Excessive light causes light stress, which shows as bleaching (white tips), leaf curling, or foxtailing.
If your DLI exceeds 65 mol/m²/day, reduce intensity by raising the light or dimming it.
Yes.
Photoperiod cannabis plants begin flowering when they receive 12 hours of uninterrupted darkness.
This mimics the shorter days of autumn.
It's crucial that the dark period is truly uninterrupted – even brief light exposure can disrupt flowering.
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