Grow Light Calculator
By Grow Area
Calculate grow light wattage needed for your space
Number of Lights Needed
Calculate how many individual lights to buy
Formula
Total Watts = Area (sq ft) × Watts per sq ft / Light Efficiency | PPFD Target: Seedlings 200, Greens 300, Fruiting 500+ µmol/m²/s
Frequently Asked Questions
How many watts per square foot for grow lights?
For LED grow lights: Seedlings need 20-30W/sq ft, leafy greens need 25-35W/sq ft, fruiting vegetables need 35-50W/sq ft. These are actual wall watts, not equivalent watts. LED is the most efficient option for indoor growing.
How high should grow lights be above plants?
LED panels: 12-24 inches above canopy. T5 fluorescent: 4-8 inches. CFL: 6-12 inches. HPS/MH: 18-36 inches. Start higher and lower gradually - if leaves curl or bleach, raise the light.
How many hours of light do indoor plants need?
Most vegetables need 14-16 hours of light per day. Fruiting crops: 16 hours in veg, 12 hours for fruiting. Herbs and greens: 12-16 hours. Seedlings: 16 hours. Always provide at least 8 hours of darkness for plant rest.
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