Cannabis Grow Tent Lighting Setup: Watts, Height, Schedule

Cannabis Grow Tent Lighting Setup

A cannabis grow tent lighting setup comes down to three numbers: how many watts your tent needs, how far the fixture hangs from the canopy, and how many hours it runs each day. For a modern LED, plan 30 to 40 watts per square foot of floor space. Hang seedlings 24 to 36 inches below the light, move to 18 to 24 inches in vegetative growth, and finish at 12 to 18 inches in flower. Run 18 hours on and 6 off during veg, then flip to 12 on and 12 off to trigger flowering.

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Before you start

• Tent with a known footprint, measured in feet
• LED or HPS fixture rated for that footprint
• Ratchet hangers or adjustable rope clips
• 24-hour mechanical timer
• Exhaust fan and carbon filter sized to tent volume
• Thermometer, hygrometer, and a light meter or PPFD phone app

Step-by-step setup

1. Measure the tent length and width, then multiply them to get square feet (a 4x4 tent is 16 square feet).
2. Multiply square feet by 30 for LED or 50 for HPS to get your target wattage (16 square feet needs about 480 LED watts).
3. Pick a fixture whose real draw from the wall meets that target, not the marketing equivalent.
4. Attach ratchet hangers to the top frame bars of the tent.
5. Hang the fixture centered over the grow area.
6. Turn the dimmer or driver to its lowest setting before plants go in.
7. Set the light 24 to 36 inches above seedlings and clones.
8. Plug the fixture into the timer and set 18 hours on, 6 hours off.
9. Raise the dimmer as plants establish, keeping 18 to 24 inches of clearance through veg.
10. Switch the timer to 12 hours on, 12 hours off on the day you want flowering to begin.
11. Lower the light to 12 to 18 inches during the stretch, then leave the height fixed.
12. Check canopy temperature and leaf color each morning; raise the light or dim it if tips bleach, curl, or dry out.

Light intensity by stage

• Seedlings and clones: 200 to 400 PPFD, 18/6 schedule
• Vegetative growth: 400 to 600 PPFD, 18/6 schedule
• Flowering: 600 to 900 PPFD, 12/12 schedule
• Late flower with CO2 supplementation: up to 1,000 to 1,200 PPFD

Intensity and distance work together. A dimmed fixture hung close delivers the same PPFD as a full-power fixture hung high, but the close setup spreads light over a smaller area and creates a hotter center hotspot. Measure at canopy level in several spots, not just under the middle of the tent.

complete indoor cannabis grow tent kit

Heat and airflow

Lights are the main heat source in a sealed tent. Mount the exhaust fan at the top, where hot air collects, and pull air through a lower passive intake vent. Keep canopy temperature between 75 and 85 F with lights on, and let it drop 5 to 10 F at night. If the tent runs hot, increase extraction before you dim the light, since dimming cuts yield potential. A small oscillating fan moving air across the canopy prevents heat pockets and strengthens stems.

complete indoor cannabis grow tent kit

Common mistakes

• Buying a fixture by watt-equivalent claims instead of actual wall draw
• Hanging a strong light at full power over seedlings
• Running 12/12 too early and losing vegetative yield
• Leaving light leaks in the tent during the dark period, which can stall flowering
• Ignoring the distance chart that ships with the fixture