Par Measurement Science on lighting
What's Happening
PAR (Photosynthetically Active Radiation) defines the spectral range of light wavelengths (400-700 nanometers) that plants use for photosynthesis. Within this range, chlorophyll pigments absorb photons to drive the light-dependent reactions of photosynthesis. The most accurate measurement is PPFD (Photosynthetic Photon Flux Density), counted in μmol/m²/s (micromoles of photons per square meter per second). Unlike human-perceived brightness, PPFD directly quantifies the number of usable photons striking a leaf surface.
How to Fix It
- 1
Purchase a dedicated PAR meter with calibrated quantum sensor for accurate PPFD readings
- 2
Measure PPFD at plant canopy height—position sensor where leaves receive light
- 3
Target PPFD ranges: Low light plants 50-150 μmol/m²/s; Medium 150-300; High 300-600; Full sun crops 600+
- 4
Calculate DLI by multiplying PPFD × hours of light × 0.0036 (conversion factor). Target DLI: Low plants 5-10 mol/m²/day; Medium 10-20; High 20-40
How to Prevent It
Invest in a PAR meter with quantum sensor for any serious indoor growing. Measure light at plant canopy level. Track DLI (Daily Light Integral) to ensure cumulative daily light targets are met.