Top pick: 700 W bar LED for a 4x4 to 5x5 flower room

Start here. A 700 W bar fixture with a photon efficacy of 2.8 µmol/J emits about 1,960 µmol/s of PPF. Spread over a 5x5 ft canopy, that works out to 845 µmol/m²/s at full power and a daily light integral of 36.5 mol/m²/day on a 12/12 schedule. That number sits inside the flower range for cannabis. Bars hold the center-to-edge drop under 15 percent. A single center cluster does not.

Look for 0 to 100 percent dimming, an IP65 rating, a remote driver, and a 5 year warranty. Street price for the fixture runs $550 to $700.

Option 2: 480 W bar LED for a 4x4 tent

Same bar layout in a smaller frame. 2.8 µmol/J, 1,344 µmol/s of PPF, 902 µmol/m²/s across 16 sq ft. DLI lands at 39 mol/m²/day at full power. Dimming to 80 percent brings it to 31. Good for a 4x4 or a 4x5 with light loss at the edges. Price band: $400 to $520.

Option 3: 320 W board for a 3x3

Two or four quantum boards on one frame. 2.6 µmol/J, 832 µmol/s, 995 µmol/m²/s over 9 sq ft. Run it at 75 percent to hit 30 mol/m²/day. Fewer bars means more shadow under the canopy, so defoliate before week 3 of flower. Price band: $260 to $340.

Option 4: 240 W board for a 2x4

2.6 µmol/J, 624 µmol/s, 840 µmol/m²/s over 8 sq ft. DLI of 36 at full power. This is the pick for a closet or a 2x4 tent. Price band: $180 to $250.

Option 5: 100 W board for a 2x2 veg or clone space

2.5 µmol/J, 250 µmol/s, 672 µmol/m²/s over 4 sq ft. Use it for veg at 18/6 or for mothers. It will not carry a 2x2 through flower. Price band: $80 to $130.

What the numbers mean

Electricity cost per month

Rates vary by state. The U.S. average residential rate sits near 16 cents per kWh.

Spectrum and schedule

Cannabis is a short-day plant. Flower at 12 hours light and 12 hours dark. Veg at 18/6. A white plus red blend covers both stages. Blue at 400 to 500 nm drives veg growth. Red at 600 to 700 nm drives flowering. Far-red at 730 nm sits at the edge of most PAR meter response. Treat added far-red as one variable and change one thing at a time.

Heat and ventilation

Bar fixtures spread heat across the tent instead of pooling it in the center. A 700 W unit adds about 2,390 BTU/hour. That is 700 W times 3.41. A 4 in inline fan moves 190 CFM, a 6 in fan moves 400 CFM. Size the fan to the tent volume and the filter, not to the light wattage.

Verdict

Buy the 700 W bar unit for a full flower room. Use the 320 W board for a 3x3 and the 240 W board for a 2x4. Size the fixture to the canopy, then dim to hit 30 to 45 mol/m²/day. A larger fixture at 70 percent output draws the same power as a smaller fixture at 100 percent and leaves headroom for later.