How to Choose a Grow Light
The single biggest factor in your yield is light. Not nutrients, not genetics — light. Getting this right before you buy saves you from the most expensive mistake in home growing.
Wattage vs. Coverage
Manufacturers advertise "equivalent" wattages that mean nothing. What matters is actual draw watts and the flowering footprint — the area the light can actually cover at full intensity during flower. A 200W light covering a 3×3 is very different from a 200W light rated for a 4×4.
Efficacy: The Number That Actually Matters
Efficacy is measured in µmol/J (micromoles per joule). It tells you how efficiently the light converts electricity into usable plant light. Anything above 2.5 µmol/J is excellent. Below 2.0 µmol/J and you're leaving yield on the table.
Spectrum Type
- Full Spectrum — white light covering the full PAR range. Best all-around for veg and flower.
- Enhanced Spectrum — adds UV and/or far-red for terpene production and faster flowering.
- Targeted — tuned for specific growth stages. Less common in home grows.
Quick Sizing Guide
- 2×2 tent — 100–150W actual draw
- 3×3 tent — 200–300W actual draw
- 4×4 tent — 400–600W actual draw
- 5×5 tent — 600–800W actual draw