PAR and PUR Explained: Understanding Reef Lighting Metrics

Serious reef keepers look beyond simple wattage to PAR and PUR measurements when evaluating lighting for coral growth.

What Is PAR?

Photosynthetically Active Radiation (PAR) measures the intensity of light within the wavelength range plants and coral actually use for photosynthesis, giving a far more useful picture than raw wattage.

What Is PUR?

Photosynthetically Usable Radiation (PUR) goes a step further, measuring how much of that PAR light falls within the specific wavelengths a given coral’s zooxanthellae can actually use effectively.

Why This Matters for Stocking

Different coral types need different PAR levels — soft corals generally thrive at lower PAR than demanding SPS species like those in our Acropora care guide, which often need considerably higher intensity.

Measuring PAR in Your Tank

A dedicated PAR meter lets you map actual light intensity at different depths and positions in your tank, helping you place coral appropriately rather than guessing based on fixture specifications alone.

See our broader aquarium lighting guide for choosing a fixture in the first place.