What Size Panel LED Grow Light Do I Need?

Nov. 03, 2025

Match wattage and PPFD to your footprint and growth stage. For modern high-efficiency panels (≥2.5 μmol/J), plan ~15–25 W/ft² for veg and 30–40 W/ft² for flower, then fine-tune with a PPFD meter.

Quick Sizing Table (Most-Searched Footprints)

Grow Area	Veg (W)	Flower (W)	Notes
2×2 ft (0.6×0.6 m)	80–120	120–200	One compact panel; watch center hotspot
3×3 ft (0.9×0.9 m)	150–220	240–320	Best value zone for panels
2×4 ft (0.6×1.2 m)	160–240	240–350	Consider two smaller panels for edges
4×4 ft (1.2×1.2 m)	260–400	400–600	Two panels spaced apart = better uniformity
5×5 ft (1.5×1.5 m)	400–550	600–800	Panels work, bars often win for uniformity

If efficacy is <2.4 μmol/J, size toward the high end. With ≥2.8 μmol/J, you can hit targets with fewer watts.

PPFD & DLI Targets (Copy/Paste Formula)

Veg: 300–600 μmol/m²/s
Flower: 700–1,000 μmol/m²/s (consider CO₂ if you run >900)

DLI = PPFD × hours × 0.0036

Example (flower): 800 PPFD × 12 h × 0.0036 = 34.6 DLI
Example (veg): 450 PPFD × 18 h × 0.0036 = 29.2 DLI

Why this matters: DLI ties light intensity and photoperiod to plant demand, so you size the panel and schedule together.

Panel vs Bar for Your Space (Fast Answer)

Panels: Best for 2×2, 3×3, 2×4—compact, budget-friendly, easy to mount.
Bars: Superior uniformity in 4×4–5×5 and larger; fewer hotspots at the same PPFD.
HPS: Legacy; high heat, bulb swaps—use only if you need the heat.

Hanging Height & Dimmer Settings

Veg: Start 18–24 in (45–60 cm) above canopy at 40–70% power.
Flower: 12–18 in (30–45 cm) targeting 700–900 PPFD to start.
Fine-tune by meter and leaf response: If edges lag, raise 1–2 in or split into two panels for coverage.

Spectrum That Works (Without the Hype)

Full-spectrum white for seedling → harvest.
660 nm deep red improves flowering efficiency.
730 nm far-red: Use sparingly (end-of-day or separate channel) to influence morphology.
UV-A (365–405 nm): Optional; can boost secondary metabolites—limit exposure.

Mini Buyer’s Checklist (SEO-Friendly)

Must-haves

Efficacy ≥2.5 μmol/J
Honest PPFD maps for your footprint (look for min/avg ≥0.6–0.7)
Dimming (0–10 V or onboard knob)
Reliable driver (e.g., Mean Well/Inventronics), 3–5 year warranty

Nice-to-haves

Detachable/external driver (cooler canopy)
Far-red/UV on separate channels
Daisy-chain control or smart scheduling (sunrise/sunset ramps)

Common Mistakes (and Easy Fixes)

Sizing by watts only → Verify PPFD and uniformity; watts vary with efficacy.
Single big panel in a wide tent → Split into two panels or consider bars for edge PPFD.
Mounting too close → Bleaching; raise fixture 2–4 in or dim 10–20%.
Ignoring climate → Light doesn’t fix VPD/temps/CO₂. Dial environment first.

Example Setups (Realistic Targets)

3×3 flower: 300 W panel at ~14–16 in, dimmed to hit 800–850 PPFD avg, DLI ~34–36.
2×4 veg: 240–300 W (two 120–150 W panels) ~20 in, 450–550 PPFD avg, DLI ~29–36 (18/6).

FAQs

Q1: Can one panel cover a 4×4 for flower?
Yes—400–600 W high-efficiency can work, but two panels usually give better edge coverage.

Q2: Do I need CO₂?
Above ~900–1,000 PPFD, CO₂ (800–1,200 ppm) helps plants use extra light—only if temps, VPD, and nutrition are tuned.

Q3: Are “blurple” panels still relevant?
No. Modern full-spectrum white panels outperform them in efficiency and plant morphology.

Q4: How long will a good panel last?
Often >50,000 hours to ~80% output if kept cool and clean.

TL;DR

1) Measure the footprint, 2) pick panel wattage using the table, 3) verify PPFD/uniformity, and 4) tune height/dimmer to hit DLI. Get those right and a panel LED grow light will deliver consistent, efficient results in small to mid-size spaces.

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