Question 1

What is PPFD and how does it affect plant growth?

Accepted Answer

PPFD (Photosynthetic Photon Flux Density) measures the amount of light available for photosynthesis in μmol/m²/s. Leafy greens need 150–250 μmol/m²/s; fruiting crops need 400–600 μmol/m²/s. Too little light causes stretching and low yield; too much causes light burn.

Question 2

What efficacy should I look for in a grow light?

Accepted Answer

Budget LEDs deliver around 1.5 μmol/J — adequate for herbs and leafy greens. Mid-range fixtures at 2.0–2.5 μmol/J are suitable for most home grows. Premium LEDs above 2.5 μmol/J are worth the investment for fruiting crops or commercial use.

Question 3

How many hours of light do plants need per day?

Accepted Answer

Leafy greens and herbs grow well on 14–16 hours per day. Fruiting crops like tomatoes and chili need 16–18 hours during vegetative growth and a 12-hour dark period to trigger flowering. Always allow an 8-hour dark period minimum — continuous light stresses most plants.

Grow Light Calculator

Grow Light Calculator