400 Watt LED Grow Lights for 3x3 & 3x4 Canopy Grows
400W LED grow lights occupy the space between compact hobby panels (200-300W for 2x2 to 2x4 canopies) and the 600W+ fixtures designed for full 4x4 flowering footprints. At 400W, a quality LED at 2.7+ umol/joule produces approximately 1,000-1,100 umol/s of total photon output -- ideal for a 3x3 ft canopy at 900-1,000 umol/m2/s PPFD, or a 3x4 ft canopy at slightly lower intensity. For growers working in a 3x3 tent, a dedicated veg room with moderate intensity requirements, or a second fixture supplementing a larger primary system, the 400W class fills the gap efficiently.
400W LED Applications: 3x3 Tents & Dedicated Veg Rooms
The most common applications for 400W LEDs: a single-fixture 3x3 ft flowering setup for growers who want meaningful production in a compact footprint; a dedicated vegetative room providing 400-600 umol/m2/s across a larger area than a flowering-intensity fixture requires; or a supplemental fixture filling coverage gaps in a larger multi-light system. For a 3x3 tent, a 400W fixture at 2.7+ umol/joule hits the productive flowering PPFD range (800-1,000 umol/m2/s) at standard 18-22 inch hanging height. For veg rooms, the same fixture hung higher covers a larger footprint at the lower vegetative PPFD target. Use our PPFD & Light Coverage Calculator to confirm coverage for your specific tent dimensions and target intensity.
400W LED Brands
Quality 400W LED grow lights from HLG (HLG 300 V2 at ~300W is the closest standard model for 3x3 coverage), Growers Choice (ROI-E420 at 420W), and comparable fixtures from qualified brands in the 380-450W class cover the 3x3 to 3x4 canopy range effectively at 2.5-2.9+ umol/joule efficiency. Browse the full LED grow lights collection to filter by wattage range. Expert support available.
400W LED Grow Light FAQ
What canopy size does a 400W LED cover?
A quality 400W LED at 2.7+ umol/joule covers a 3x3 ft canopy at 900-1,000 umol/m2/s PPFD for flowering, or a 3x4 ft canopy at 750-850 umol/m2/s -- adequate for production at lower intensity targets. For vegetative growth targeting 400-600 umol/m2/s, a 400W fixture covers a 4x4 ft area adequately when hung slightly higher. Always verify using the manufacturer's published PPFD map at your target hanging height rather than estimating from wattage alone.
Is 400W enough for flowering?
Yes, for a 3x3 ft canopy. A 400W LED at 2.7+ umol/joule delivers 900-1,000 umol/m2/s PPFD across a 3x3 ft footprint at 18-22 inches -- sufficient for productive flowering for most crops. For a 4x4 tent, a 400W fixture will not cover the full footprint at flowering PPFD and should be replaced with a 600-800W fixture for complete 4x4 coverage. If you are unsure whether a specific 400W fixture provides adequate coverage for your canopy, use our PPFD Calculator with the manufacturer's PPFD data.
