PAR Meter
A PAR meter is a specialized handheld measuring device used to quantify photosynthetically active radiation, the specific range of light wavelengths corals and their symbiotic zooxanthellae actually use for photosynthesis, at specific points within a reef tank. Rather than relying on general assumptions about lighting equipment output, a PAR meter gives reef keepers precise, measurable data about the light intensity a coral is actually receiving at its exact placement location.
PAR meters have become increasingly accessible and affordable in recent years, making direct PAR measurement a realistic option for hobbyists who once relied primarily on general placement guidelines and observation alone.
Why It’s Important
- Provides precise, measurable data rather than relying on assumptions about lighting output.
- Helps confirm whether a specific coral is receiving appropriate light intensity.
- Useful for mapping variation in PAR throughout different zones of a tank.
- Has become increasingly affordable and accessible for hobbyist use.
How It Works
A PAR meter’s sensor detects light specifically within the photosynthetically useful 400 to 700 nanometer wavelength range, converting that measurement into a numerical reading typically expressed in micromoles per square meter per second. Reef keepers position the sensor at the exact point where a coral sits, accounting for water depth and any shading from rockwork or other corals, to get an accurate, location-specific reading.
Because PAR can vary significantly even within a single tank depending on depth, distance from the light source, and surrounding shade, taking multiple readings across different zones gives a much more complete picture than relying on a single measurement near the water’s surface.
PAR Meter and Related Concepts
A PAR meter is closely tied to PAR itself, the measurement it’s specifically designed to capture, and to photosynthesis and coral placement, the concepts most directly informed by its readings. It’s also relevant to lighting fixtures and coral coloration, since appropriate PAR delivery significantly affects both growth and pigmentation.
Reef keepers setting up a new tank or introducing an unfamiliar coral species often use a PAR meter to confirm a proposed placement location falls within that species’ known appropriate PAR range before committing to it long-term.
Regularly checking PAR readings over time also helps reef keepers notice gradual changes, such as declining output as an LED fixture ages, allowing for timely adjustments before coral health is meaningfully affected by insufficient lighting.
Some PAR meters also offer spectral readings beyond a single overall number, giving more advanced reef keepers additional insight into the specific wavelength composition of their lighting rather than just total photosynthetically useful intensity.
Common Misconception
A common misconception is that a PAR meter reading taken once at setup remains accurate indefinitely. In reality, lighting output can drift over time due to fixture aging or dust accumulation, making periodic re-measurement worthwhile for maintaining consistent, appropriate coral lighting.
The Bottom Line
A PAR meter is a specialized device that measures photosynthetically active radiation at specific points within a reef tank. Using one gives reef keepers precise, actionable data for matching lighting intensity to each coral’s actual needs.
