Top pick

A 4-foot LED bar fixture at 150W to 200W with a dimmer, 4000K to 5000K diodes, and a PPF near 300 µmol/s is the best light for mother plants. Hang it 18 to 24 inches above the canopy and set output to 200 to 400 PPFD. That range holds a mother in vegetative growth, keeps node spacing tight, and draws 40 percent to 60 percent less wall power than a 4-bulb T5 HO fixture of the same footprint.

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Dimming is the deciding feature. A mother plant does not need full output. It needs a stable, repeatable light level that keeps cuts easy to take every 3 to 6 weeks. A dimmable bar lets you match output to plant size and room temperature without moving the fixture.

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What a mother plant needs

  • PPFD: 200 to 400 µmol/m²/s at the canopy
  • DLI: 12 to 20 mol/m²/day
  • Photoperiod: 18 hours on, 6 hours off
  • Spectrum: 4000K to 6500K, blue share above 20 percent
  • Air temp: 75F to 80F. Leaf temp within 2F of air temp
  • Humidity: 55 to 65 percent

Mothers are not grown for yield. Light above 600 PPFD pushes thick stems and tight nodes, but it also raises water use, nutrient demand, and pruning work. Most home growers run 18/6 rather than 24/0 to cut power cost and give the plant a dark cycle.

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The options

1. 4-foot LED bar, 150W to 200W, dimmable (top pick)

  • PPF: 300 to 500 µmol/s depending on wattage
  • Efficacy: 2.5 to 2.9 µmol/J
  • Coverage: 4 ft by 2 ft at 18 inches
  • Dimming: 10 to 100 percent
  • Heat: passive, no ducting needed
  • Lifetime: diode ratings list 50,000 hours at L90

Run at 50 to 70 percent output for one or two mothers. Spread is even across the bar, so lower branches get light without a reflector hot spot.

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2. T5 HO fluorescent, 4 ft, 4 bulbs

  • Draw: 216W
  • PPF: about 240 µmol/s total
  • Efficacy: 1.0 to 1.2 µmol/J
  • Coverage: 4 ft by 2 ft
  • Heat: warmer than LED, cooler than CMH
  • Tube replacement: every 12 to 18 months

Low upfront cost and even spread. Output drops as tubes age, and the fixture puts heat into the canopy instead of above it. Best for a clone and mother rack on a tight budget.

3. 315W CMH

  • Draw: 315W
  • PPF: 500 to 560 µmol/s
  • Efficacy: 1.6 to 1.8 µmol/J
  • Coverage: 3 ft by 3 ft
  • Clearance: 24 to 30 inches
  • Lamp replacement: 20,000 hours

Strong output for a large mother room. Runs hot, needs ventilation, and costs more to operate than LED at the same PPF.

4. 100W quantum board

  • PPF: 230 to 270 µmol/s
  • Efficacy: 2.3 to 2.7 µmol/J
  • Coverage: 2 ft by 2 ft in veg
  • Dimming: 20 to 100 percent on most models

Fits one or two mothers in a tent. Small footprint means you buy two boards for a 4-foot shelf.

How to compare fixtures

  1. PPF in µmol/s. Wattage alone says nothing about light output.
  2. Efficacy in µmol/J. Higher number means less power per unit of light.
  3. Footprint at 18 inches. Check the PPFD map, not the marketing square footage.
  4. Dimming range. A 10 percent floor beats a 50 percent floor for small mothers.
  5. Heat load. CMH adds 315W of heat. LED adds 150W to 200W.
  6. Warranty. Look for 3 to 5 years on the driver and board.
  7. Replacement parts. Diodes last. Tubes and lamps do not.

Manufacturer PPF figures vary 10 to 15 percent from third-party tests. Treat published numbers as a range, not a guarantee.

Setup numbers

  • LED bar: 18 to 24 inches above the canopy, 200 to 400 PPFD
  • T5 HO: 8 to 12 inches above the canopy
  • CMH: 24 to 30 inches above the canopy
  • Timer: 18/6, checked every 2 weeks for drift
  • Meter: quantum sensor such as Apogee or LI-COR, or a phone app with a diffuser. Phone apps read within 10 to 15 percent of a calibrated sensor.

Yearly power cost

At 18 hours per day for 365 days and $0.15 per kWh:

  • 150W LED: 985 kWh, about $148 per year
  • 216W T5 HO: 1,419 kWh, about $213 per year
  • 315W CMH: 2,070 kWh, about $310 per year

A 150W LED saves about $65 per year against T5 HO and about $162 per year against CMH, on one fixture.

Maintenance

  • Wipe the diode face and heat sink every 4 to 6 weeks. Dust cuts output.
  • Replace T5 tubes at 12 to 18 months.
  • Replace CMH lamps at 20,000 hours or when PPF drops below 80 percent of the original rating.
  • Log PPFD readings and photoperiod changes. A mother room fails on drift, not on failure.

Bottom line

Buy the 4-foot dimmable LED bar in the 150W to 200W class for a mother room of 4 square feet or more. Choose a 100W board for one or two mothers in a 2-foot tent, T5 HO for the lowest upfront cost, and CMH only if you already own the ballast and vent the heat.