Best Grow Lights for Indoor Greenhouses: Compare Technologies & Costs

Light drives photosynthesis. In an indoor greenhouse, your fixture choice determines whether seedlings stretch, stall, or thrive. Four technologies dominate. Here's how they stack up for plant performance, operating cost, and practical fit.

Incandescent: Obsolete for Growing

Low output, wrong spectrum (red-heavy, blue-deficient), 90% energy wasted as heat. Useful only for decorative display lighting. Not a grow light.

Metal Halide (MH): The Gold Standard for Vegetative Growth

CRI 65–80 (horticultural grades hit 80+). Broad, sun-like spectrum drives robust leaf/stem development. 400W covers 4×4 ft. Runs hot—needs ventilation. Bulb life: 10,000–20,000 hrs. Higher upfront cost, but unmatched for structure-building phase.

High-Pressure Sodium (HPS): Flowering & Fruiting Specialist

Peak output in orange/red (590–620 nm)—triggers bloom/fruit set. Poor blue output = leggy growth if used alone. Best paired with MH (dual-arc fixtures) or supplemental fluorescent. Horticultural HPS improves spectrum balance. 1000W covers 5×5 ft.

Fluorescent (T5 HO & Compact): The Value Champion

Full-spectrum horticultural tubes (6500K veg, 3000K bloom) deliver usable PAR with minimal heat. T5 High Output: 54W/4-ft tube, 5,000 lumens. Run 2–4 inches from canopy. Cool enough for shelves. 20,000+ hr life. Lowest $/µmol. Ideal for seedlings, microgreens, herbs, leafy crops.

LED: The Rising Contender

Tunable spectrum, high efficiency, minimal heat, 50,000+ hr life. Quality varies wildly. Look for: Samsung/Osram/Cree diodes, published PPFD maps, passive cooling, 5+ yr warranty. Currently 2–3× fluorescent cost per µmol. Best for multi-layer racks where heat removal is costly.

Match Light to Crop & Stage

Seedlings/veg: Fluorescent or MH. Flower/fruit: HPS or full-spectrum LED. Mixed crops: Dual MH/HPS or tunable LED. Budget + space + crop = your answer. Measure PPFD at canopy—don't trust wattage claims.