☀️ DLI Calculator
Convert PPFD to Daily Light Integral (mol/m²/day) and get optimal DLI ranges for every cannabis growth stage
Calculate Your DLI
Enter your light meter reading or estimated PPFD
Hours of light per day (18/6 for veg, 12/12 for flower)
Your DLI Results
Recommendation:
Note
DLI is a more accurate measure of total light delivery than PPFD alone because it accounts for photoperiod length.
PPFD ↔ DLI Reference Table
DLI values (mol/m²/day) for common PPFD levels at 12-hour and 18-hour photoperiods.
| PPFD (µmol/m²/s) | DLI at 12h | DLI at 18h |
|---|
THE MORE YOU KNOW: DLI
What is DLI?
Daily Light Integral (DLI) measures the total number of photosynthetically active photons (PAR) delivered to a square meter over a full day. It is expressed in moles of light per square meter per day (mol/m²/day). Think of PPFD as the speed of light delivery and DLI as the total distance traveled -- DLI tells you the full picture of how much light your plants actually receive in 24 hours.
Why DLI Matters More Than PPFD
PPFD only tells you the intensity of light at a single moment. Two growers could have the same PPFD of 600 µmol/m²/s, but if one runs an 18/6 light schedule and the other runs 12/12, their plants receive vastly different amounts of total light. DLI accounts for both intensity and duration, making it the superior metric for optimizing plant growth, yield, and quality.
How to Measure PPFD
The most accurate way to measure PPFD is with a quantum PAR meter (such as Apogee MQ-500 or Photobio). Place the sensor at canopy level, directly under the light, and take multiple readings across your grow space. For a rough estimate, check your grow light manufacturer's PPFD map, which shows intensity at various distances and positions. Some smartphone apps can also provide approximate PAR readings.
Common Grow Lights and Typical PPFD Values
LED panels (modern full-spectrum): 400-1000 µmol/m²/s at 12-18 inches. HPS 600W: 600-900 µmol/m²/s at 12-18 inches. HPS 1000W: 800-1200 µmol/m²/s at 18-24 inches. CMH 315W: 400-700 µmol/m²/s at 18-24 inches. CFL/T5 fluorescent: 100-300 µmol/m²/s at 6-12 inches. These values vary greatly based on hanging height, reflector quality, and light age.
HOW TO USE THIS Calculator
- Measure or estimate your PPFD at canopy level using a PAR meter, manufacturer specs, or a smartphone app
- Enter the PPFD value in micromoles per square meter per second (µmol/m²/s)
- Enter your photoperiod -- the number of hours your lights are on per day (18 for veg, 12 for flower)
- Select your current growth stage to see the target DLI range
- Click "Calculate DLI" to see your Daily Light Integral and whether it falls within the optimal range
- Follow the adjustment recommendations if your DLI is below or above the target range
CALC'S FAQ HOTLINE
What is DLI and why does it matter for cannabis?
DLI (Daily Light Integral) measures the total amount of photosynthetically active light delivered to a plant each day, expressed in mol/m²/day. It matters because it accounts for both light intensity (PPFD) and duration (photoperiod), giving a complete picture of light delivery. Two grows with the same PPFD but different photoperiods will have very different DLI values and plant responses.
Is this tool free to use?
Yes! This tool is completely free with no hidden costs, subscriptions, or limitations. Use it as often as you need.
Do I need to create an account?
No account needed. The tool works entirely in your browser without requiring signup or personal information.
Does this work on mobile devices?
Yes, this tool is fully responsive and works on smartphones, tablets, and all desktop browsers.
Is my data private?
Absolutely. All processing happens locally in your browser. Your data never leaves your device and is not stored on any server.
How do I measure PPFD without a light meter?
If you don't have a PAR meter, check your grow light manufacturer's PPFD map or specs sheet. Many manufacturers provide PPFD values at specific hanging heights. You can also use smartphone apps as a rough estimate, though dedicated PAR meters are more accurate. Common PPFD ranges: LED panels 400-900 µmol/m²/s, HPS 600-1000 µmol/m²/s at canopy level.