Aquarium Lighting: Spectrum, Intensity & Photoperiod

Plants use red (660nm) and blue (450nm) wavelengths most efficiently. Green light is mostly reflected (why plants are green), but some green light penetrates deeper in water. Full-spectrum LEDs that include red, blue, and green produce good plant growth and natural fish coloration. Avoid lights labeled "actinic" or super-blue except for saltwater — freshwater plants grow poorly under blue-only light.

• Fish-only freshwater: Any basic LED is fine. Aim for low to moderate intensity (20-40 PAR). Too much light causes algae without plant competition.
• Low-tech planted (no CO2): 20-50 PAR at substrate. Use medium intensity LED. Limit photoperiod to 6-7 hours.
• High-tech planted (with CO2 injection): 50-150 PAR at substrate. High-output LEDs or T5 fluorescent. Requires CO2 supplementation to match high light, or algae will dominate.
• Saltwater reef (with corals): 100-300 PAR for LPS/soft corals, 300-600+ PAR for SPS corals. Specialized reef LED fixtures with adjustable spectrum.

Standard LED strips: Best for beginners and low-light planted tanks. Inexpensive, energy-efficient, long-lasting (50,000+ hours). Example: Nicrew, Fluval Plant Nano, AquaSky. For 20-gallon standard tank, a 20-30 watt LED is adequate for low-light plants.

High-output LEDs: For medium to high-light planted tanks. Dimmable, often with programmable timers and spectrum control. Examples: Chihiros WRGB, Twinstar, Fluval Plant 3.0, Kessil A360X. Higher upfront cost ($150-400) but better plant growth and color rendering.

T5 Fluorescent: Older technology but still excellent for plant growth. High output, even coverage. Bulbs need replacement every 9-12 months (spectrum shifts).

Refugium lights (saltwater): Specialized red-spectrum LEDs for growing macroalgae in sumps.

Photoperiod = hours of light per day. For low-tech tanks: 6-8 hours. For high-tech (with CO2): 8-10 hours. Never exceed 10 hours in any planted tank. Use a timer — consistency is critical. A split photoperiod (4 hours on, 2 off, 4 on) can help algae control by interrupting continuous exposure, but plants adapt to any schedule. "Sunrise/sunset" dimming features (available on many LEDs) reduce stress for fish and prevent sudden algae triggers from instant bright light.

Too much light: Green hair algae, spot algae on glass, plants turn yellow/pale (photoinhibition). Solution: reduce intensity (dim light) or raise fixture height, or reduce photoperiod.

Too little light: Plants grow leggy (long stems with few leaves), bottom leaves die, slow growth, no pearling (oxygen bubbles). Solution: upgrade light or move fixture closer to water surface.

Wrong spectrum: Plants appear dull brown/grey. Fish colors wash out. Solution: choose 6500K-7500K full-spectrum light.

Carpeting plants (Dwarf baby tears, Monte Carlo, Glossostigma) require high light (80-120 PAR at substrate) AND CO2 injection. Without both, they won't carpet — they'll grow upward or die. For low-tech tanks, use easier carpets like Marsilea hirsuta or Microsword, which tolerate lower light.

While you can use shop LED lights (5000K-6500K), they often lack sufficient PAR for plants beyond 12 inches depth. They also aren't waterproof — humidity damages them quickly. If budget is tight, use a hygger or Nicrew submersible LED (safe, cheap). For a 10-gallon tank, a simple clip-on LED grow bulb (6500K) in a desk lamp works for easy plants.