Light is the energy currency of photosynthesis. In indoor hydroponics, your lighting system replaces the sun—and the quality of that replacement determines every outcome. This guide covers the full spectrum of horticultural lighting technologies, from legacy to leading-edge.
Lighting Technology Comparison
Incandescent/Incandescent-Halogen
- Spectrum: Red-heavy, deficient in blue
- Efficiency: ~15 lm/W (terrible)
- Heat: Extreme
- Verdict: Obsolete for horticulture. Avoid.
Fluorescent (T5, T8, CFL)
- Spectrum: Configurable (cool/daylight/warm)
- Efficiency: 60-100 lm/W
- Penetration: Poor (>6-8" canopy depth)
- Best for: Seedlings, cuttings, microgreens, low-light herbs
- High-Output T5: 5,000 lm per 54W; thin profile for low ceilings
High-Intensity Discharge (HID)
Metal Halide (MH)
- Spectrum: Blue-white (summer sun simulation)
- Efficiency: 70-115 lm/W
- Best for: Vegetative growth, compact structure
- Bulb life: 12-18 months
High-Pressure Sodium (HPS)
- Spectrum: Red-yellow (autumn sun simulation)
- Efficiency: 97-150 lm/W
- Best for: Flowering/fruiting, maximum yield
- Bulb life: 24 months
Conversion/ Switchable Systems
Run MH or HPS on same ballast (digital). Flexible but compromised optimization.
Light Emitting Diodes (LED)
- Spectrum: Fully customizable (targeted wavelengths)
- Efficiency: 1.5-3.0+ µmol/J (photon efficacy)
- Heat: Low at canopy; heat at fixture (requires heatsink)
- Lifespan: 50,000+ hours
- Form factors: Bars, panels, COB, quantum boards
- Best for: All phases with proper spectrum; multi-layer/vertical
Sulfur Plasma / Induction
- High efficiency, broad spectrum, long life
- High cost, limited availability, fixture size
- Niche commercial applications
Selecting Your System: Decision Framework
- Define growing goals: Crop types, phases, scale, budget
- Calculate light requirements: DLI (Daily Light Integral) targets by crop
- Evaluate space constraints: Ceiling height, footprint, ventilation capacity
- Compare total cost of ownership: Fixture + bulbs + electricity + cooling + replacement over 5 years
- Consider controllability: Dimming, spectrum tuning, scheduling
Reflector and Distribution
- Air-cooled hoods: Essential for HID in confined spaces
- Light distribution uniformity: Target <15% variation across canopy
- Reflector maintenance: Clean quarterly; replace degraded surfaces
Photoperiod Management
- Vegetative: 18/6 or 20/4 (light/dark hours)
- Flowering: 12/12 (most photoperiodic crops)
- Autoflowers: 18-20/4-6 throughout
- Use digital timers or controllers—reliability is critical
Emerging LED Metrics
Move beyond watts. Evaluate:
- PPF (Photosynthetic Photon Flux): µmol/s total output
- PPFD (PPF Density): µmol/m²/s at canopy
- PPE (Photon Efficacy): µmol/J (efficiency)
- Spectrum: Photon distribution 400-700 nm
The best lighting system is the one matched to your specific crops, space, and economics. Technology evolves; principles endure. Light drives photosynthesis—everything else supports that reality.
