LED vs HPS vs CMH
Modern LED (Samsung diodes, Quantum boards)
  • Highest efficiency (2.5–3.0 µmol/J)
  • Lower heat — easier to dial in temp
  • Higher upfront cost, lower long-term
  • Best for tents and small rooms
HPS / CMH (legacy gas-discharge)
  • HPS still wins on yield per dollar in some setups
  • CMH adds UVB — better terpenes, more frost
  • Hotter — needs more venting
  • Bulbs degrade — replace yearly
Seedling PPFD
200–400
µmol/m²/s
Veg PPFD
400–600
µmol/m²/s
Flower PPFD
700–1000
µmol/m²/s
With CO₂
1200–1500
µmol/m²/s

Common mistakes

  • Running LEDs too close to seedlings (light burn)
  • Buying cheap blurple lights (low quality, low efficiency)
  • Not measuring PPFD — guessing by wattage