Light: It's Not Just Brightness

In the old days, we used "Watts per Gallon". Modern LEDs have made that rule obsolete. A 10W LED can be brighter than a 50W incandescent bulb. To understand plant growth, we need to speak the language of physics.

Key Terminology

1. Kelvin (Color Temperature)

• 6500K: "Daylight". The standard for planted tanks. Looks crisp white/yellow.
• 10000K: "Crisp White". Good for depth, enhances blues.
• 3000K: "Warm White". Very yellow, promotes algae, looks murky.

2. PAR (Photosynthetically Active Radiation)

This measures the amount of light energy that actually reaches the substrate.

• Low Light (10-30 PAR): Anubias, Ferns, Crypts.
• Medium Light (30-50 PAR): Stems, Swords.
• High Light (50+ PAR): Carpeting plants (Monte Carlo), Red plants. Requires CO2!

3. PUR (Photosynthetically Usable Radiation)

Not all light is equal. Plants mostly use Red and Blue wavelengths. Green light is mostly reflected (which is why plants look green!). A light might have high PAR but low PUR if it's mostly green light.

Photoperiod (Duration)

Consistency is key.

• New Tank: 6 hours per day.
• Established Tank: 8 hours per day.
• 10+ Hours: Algae Farm.

Use a timer. Plants have a circadian rhythm. They "wake up" and begin photosynthesis. If the light turns on and off randomly, they cannot optimize their chemical processes.

Ramping

Modern lights mimic sunrise and sunset.

• Benefit: Reduces stress for fish (sudden flash of light is terrifying).
• Aesthetic: Looks beautiful.
• Biological: Allows plants to slowly ramp up photosynthesis.