Hydroponic Lighting Guide: Spectrum, Intensity & Fixture Types

Light drives photosynthesis. In hydroponics—especially indoors—you are the sun. Choosing the right spectrum, intensity, photoperiod, and fixture determines whether plants stretch weakly or grow stocky and productive. Here’s a practical lighting masterclass.

Light Fundamentals

• Intensity: Measured in µmol/m²/s (PPFD). Leafy greens: 150–300; fruiting crops: 400–600+.
• Photoperiod: Vegetative: 18–20 hrs; Flowering/fruiting: 12 hrs. Transition gradually—sudden changes stress plants.
• Spectrum: Blue (400–500 nm) → compact, vegetative growth. Red (600–700 nm) → flowering, stem elongation. Full-spectrum white LEDs balance both.
• Placement: Keep canopy 12–24″ from LEDs; 24–36″ from HID. Adjust as plants grow. Avoid light burn (bleached, curled leaves).
• Reflectors/Hoods: Direct light downward; increase uniformity.

Fixture Technologies

Fluorescent (T5 HO, CFL)

• Pros: Low heat, affordable, good blue spectrum.
• Cons: Lower intensity; bulky; shorter lifespan (10–15k hrs).
• Best for: Seedlings, clones, leafy greens, herbs.

High-Intensity Discharge (HID)

• Metal Halide (MH) – Blue-rich; vegetative growth.
• High-Pressure Sodium (HPS) – Red-rich; flowering/fruiting.
• Pros: High output, proven track record.
• Cons: High heat, high power, ballast required, bulb degradation (replace yearly).

LED (Light-Emitting Diode)

• Pros: Tunable spectrum, low heat, high efficiency (2.5+ µmol/J), long life (50k+ hrs), plug-and-play.
• Cons: Higher upfront cost; quality varies wildly.
• Best for: All stages if full-spectrum; custom spectra for research.

Hybrid / Blended

Fixtures combining red + blue LEDs or MH + HPS in one hood. Simplifies switching but less flexible than tunable LEDs.

Matching Light to Crop & Stage

Crop Type	Vegetative PPFD	Flowering PPFD	Recommended Fixture
Lettuce, herbs, greens	150–250	N/A	T5 fluorescent / 300W LED
Tomatoes, peppers, cucumbers	300–400	500–700	600W HPS / 500W+ LED
Strawberries	250–350	400–500	400W LED / CMH
Cannabis	400–600	800–1000+	600–1000W LED / DE HPS

Pro Tips

• Use a PAR meter (or smartphone app) to verify intensity at canopy.
• Run lights on a timer—consistency is everything.
• Keep fixtures clean; dust cuts output 10–15%.
• Vent heat from HID; even LEDs need airflow.

Light is the single biggest variable you control. Invest in quality, measure your output, and adjust for each growth phase. Your plants will repay you with density, flavor, and yield.