PAR Explained: How Much Light Does Your Coral Actually Need?

Why watts and Kelvin mislead

Wattage tells you power draw, not light delivered to your coral. Kelvin describes color temperature, not intensity. Neither tells you whether your SPS frag is getting enough usable light to photosynthesize and calcify.

What PAR actually measures

PAR (Photosynthetically Active Radiation) measures the actual quantity of usable light reaching a specific point — measured with a PAR meter at coral placement depth, not at the light fixture itself. The same fixture delivers wildly different PAR at 6 inches versus 24 inches of water depth.

Rough target ranges

• Soft corals / LPS: 50–150 PAR
• Mixed reef / moderate SPS: 150–250 PAR
• High-light SPS (Acropora): 250–450 PAR, depending on species and acclimation

These are ranges, not precise targets — the bigger risk is usually moving a coral too fast from low to high PAR, not the absolute number itself. Photo-stress (bleaching from too much light too fast) is more common than under-lighting in modern reef tanks with powerful LED fixtures.

The practical approach

Acclimate new frags at lower light and ramp up gradually over 2–3 weeks. Watch coral color and polyp extension as your real-time feedback — better signals than chasing a specific PAR number from a forum post about a different tank with different water clarity.