Question 1

What is DLI (Daily Light Integral)?

Accepted Answer

DLI (Daily Light Integral) is the amount of photosynthetically active radiation (PAR) delivered to plants over a 24-hour period. It's measured in moles per square meter per day (mol/m²/day) and represents the total photons available for photosynthesis. DLI combines both light intensity (PPFD) and duration (photoperiod) into a single, easy-to-understand metric for plant lighting.

Question 2

How do you calculate DLI from PPFD?

Accepted Answer

To calculate DLI from PPFD: DLI = PPFD × Photoperiod × 3.6 ÷ 1,000,000. Where PPFD is in µmol/m²/s (micromoles per square meter per second), photoperiod is hours of light per day, and DLI is in mol/m²/day. For example, 500 µmol/m²/s for 12 hours = (500 × 12 × 3.6) ÷ 1,000,000 = 21.6 mol/m²/day.

Question 3

What is the optimal DLI for different plants?

Accepted Answer

Optimal DLI varies by plant type: Low-light plants (lettuce, herbs): 10-15 mol/m²/day. Medium-light plants (peppers, beans): 15-25 mol/m²/day. High-light plants (tomatoes, cannabis): 30-50 mol/m²/day. Seedlings: 6-12 mol/m²/day. Microgreens: 10-18 mol/m²/day. Succulents: 12-20 mol/m²/day. These ranges ensure optimal photosynthesis without light stress.

Question 4

What is PPFD and how does it relate to DLI?

Accepted Answer

PPFD (Photosynthetic Photon Flux Density) measures light intensity at a specific moment, expressed in µmol/m²/s. It's the instantaneous rate of photons hitting a surface. DLI is the accumulation of PPFD over time (24 hours). Think of PPFD as water flow rate and DLI as total water volume. You can achieve the same DLI with high PPFD for short periods or low PPFD for longer periods.

Question 5

How to calculate DLI for indoor grow lights?

Accepted Answer

For indoor grow lights: 1) Measure PPFD at plant canopy height using a quantum sensor or manufacturer specs. 2) Determine your daily photoperiod (hours lights are on). 3) Apply the formula: DLI = PPFD × Hours × 3.6 ÷ 1,000,000. For example, LED grow lights at 600 µmol/m²/s for 16 hours = 34.56 mol/m²/day, ideal for flowering tomatoes or cannabis.

Question 6

What DLI do cannabis plants need?

Accepted Answer

Cannabis DLI requirements by stage: Seedling: 12-18 mol/m²/day. Vegetative growth: 25-40 mol/m²/day. Flowering: 35-50 mol/m²/day. Professional cannabis growers often target 40-45 mol/m²/day during flowering for maximum yields. Higher DLI increases bud density and cannabinoid production, but requires proper temperature and CO₂ management to avoid light stress.

Question 7

How does photoperiod affect DLI?

Accepted Answer

Photoperiod (hours of light) directly affects DLI. Same PPFD with longer photoperiod = higher DLI. Example: 400 µmol/m²/s for 12 hours = 17.28 DLI, but for 18 hours = 25.92 DLI. However, plants may respond differently to intensity vs. duration due to circadian rhythms and photoperiodism. Short-day plants (like cannabis flowering) need specific dark periods regardless of DLI.

Question 8

What's the difference between DLI and lux?

Accepted Answer

DLI measures photosynthetically active photons over 24 hours (mol/m²/day), specifically for plant growth. Lux measures visible light intensity as perceived by human eyes (lumens/m²), not useful for plants. Lux includes green light (which humans see well but plants use poorly) and excludes UV/far-red (which affect plant growth). Always use PPFD/DLI, not lux, for grow lighting.

Question 9

How to measure DLI in my garden?

Accepted Answer

To measure DLI: 1) Use a PAR meter (quantum sensor) to measure PPFD in µmol/m²/s at plant level. 2) Take measurements every 2 hours throughout the day. 3) Calculate average PPFD. 4) Use formula: DLI = Average PPFD × Hours of daylight × 3.6 ÷ 1,000,000. Alternatively, use apps or dedicated DLI meters that automatically integrate measurements over time.

Question 10

Can you have too much DLI?

Accepted Answer

Yes, excessive DLI causes light stress, photoinhibition, and damage. Symptoms include: leaf bleaching, curling, brown spots, stunted growth, and reduced yields. Most plants have DLI saturation points: lettuce >17 mol/m²/day, tomatoes >50 mol/m²/day, cannabis >65 mol/m²/day. Excess light also increases heat and energy costs without yield benefits. Always match DLI to your specific plant's optimal range.

DLI Calculator - Daily Light Integral Calculator for Plant Growth

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DLI Calculator for Different Plant Types

Example DLI Calculation

How Our DLI Calculator Works

The DLI Formula

Understanding PPFD and DLI

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DLI Calculator Examples

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Lettuce Seedling Example

Tomato Fruiting Example

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