Free Grow Light Calculator

Calculate the perfect lighting for your indoor garden. Get DLI recommendations, coverage estimates, and find the right grow light for your plants.

Grow Light Requirements Calculator

US average: $0.12/kWh. Check your utility bill for your rate.

How Our Calculator Works

1

Enter Your Space

Tell us your grow room dimensions and what you're growing.

2

Get DLI Targets

We calculate optimal Daily Light Integral and PPFD for your plants.

3

Find Your Light

Get personalized recommendations with cost estimates.

Understanding DLI (Daily Light Integral)

DLI (Daily Light Integral) measures the total amount of photosynthetically active radiation (PAR) that plants receive during a 24-hour period. It's expressed in moles of light per square meter per day (mol/m2/d).

DLI Requirements by Plant Type

Plant Type Minimum DLI Optimal DLI
Leafy Greens 12 mol/m2/d 17-20 mol/m2/d
Fruiting Plants 20 mol/m2/d 30-40 mol/m2/d
Flowering (Cannabis) 25 mol/m2/d 40-65 mol/m2/d
Seedlings 6 mol/m2/d 10-15 mol/m2/d
Houseplants 4 mol/m2/d 8-12 mol/m2/d

How to Calculate DLI

The formula for calculating DLI is:

DLI = PPFD x (Hours of Light x 3600) / 1,000,000

Where PPFD is measured in micromoles per square meter per second (umol/m2/s). Our calculator handles all these conversions automatically to give you accurate recommendations.

Frequently Asked Questions

How many watts per square foot do I need?

For LED lights: 25-50 watts per square foot depending on plant type. Flowering plants need more (40-50W/sqft), while leafy greens need less (25-35W/sqft). HPS lights require more wattage due to lower efficiency.

How far should my grow light be from plants?

This varies by light intensity. Generally: seedlings 24-36 inches, vegetative 18-24 inches, flowering 12-18 inches. Always check your specific light's recommendations and watch for light stress (bleaching, curling).

LED vs HPS - which is better?

LED is more energy-efficient (uses 40% less electricity for same output), produces less heat, and lasts longer (50,000+ hours vs 10,000). HPS has higher initial intensity but higher running costs. For most growers, LED is the better long-term investment.

What is PPFD and why does it matter?

PPFD (Photosynthetic Photon Flux Density) measures light intensity in umol/m2/s. It tells you how much usable light reaches your plants. Higher PPFD = more photosynthesis = faster growth. Most flowering plants want 600-1000 PPFD.

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