PAR refers to Photosynthetic Active Radiation and designates the spectral range from 400–700 nm. The photons in the PAR range affect other horticulture lighting metrics such as PPF, PPE, PPFD and DLI.

PPF refers to Photosynthetic Photon Flux or a light source’s total number of photons emitted measured in micromoles per second (µmol/s). PPF traditionally only measures the number of photons in the PAR 400-700 nm range and is currently the standard measure for determining the efficacy of horticultural lighting products. Active Grow provides PPF data for both the PAR 400-700 nm and PBAR 280-800 nm ranges.

PPFD refers to Photosynthetic Photon Flux Density or the amount of photons in the PAR or PBAR range that reach a target point each second as expressed in micromoles per square meter per second (µmol/m2/s). In horticulture, PPFD maps generally include multiple target points evenly spread out covering a defined growing area (Ex. A 4′x4′ growing area with measurements taken at 6″ increments). Each target point measurement represents the amount of photons falling on the plant canopy from a given height at that specific location each second.

Active Grow provides PPFD data for many of its fixtures for different mounting heights and environments (open floor vs reflective sides). All Active Grow PPFD data uses the PBAR range.

The Emerson Effect is the increase in the rate of photosynthesis after chloroplasts are exposed to light of wavelengths 660-680 nm (red wavelengths) and 680-730 nm (far-red wavelengths) simultaneously. This combination of red and far-red wavelengths increases photosynthesis rates by up to 15%, resulting in faster grow cycles, enhanced flavonoid content and a higher percentage of trichomes in cannabis. Recent studies have shown the Emerson Effect to improve the growth rates of vegetables, flowers, fruits and other plants species.

For more information watch the video “Far-red: The Forgotten Photons” from Dr. Bruce Bugbee, the Director of the Crop Physiology Lab at Utah State University.