#### Horticultural Lighting – Definition of Terms

**Radiant Flux:** The measured radiant power of the test item in units of watts from 350nm to 850 nm.

**Luminous Flux:** The measured radiant power of the test item in units of lumens from 380nm to 780 nm.

**PPF (400-700nm):** Photosynthetic Photon Flux – Flux from 400 to 700 nm expressed in units of μmol/sec. This wavelength range has been identified as important to photosynthetic processes.

**PBAR Flux(350-800nm):** Plant Biologically Active Radiation Flux – Flux from 350 to 800 nm expressed in units of μmol/sec. Plants have photopigments other than chlorophyll that are sensitive to a wider range of wavelengths than chlorophyll.

**Radiant Efficiency:** The ratio of light flux in watts to electrical input power in watts expressed in percent.

Luminous Efficacy: The ratio of light flux in lumens to electrical input power in watts expressed in lm/W.

**PPF Efficacy:** The ratio of photosynthetic photon flux to electrical input power in watts expressed in μmol/sec/W.

**PBAR Efficacy:** The ratio of photon flux in the wavelength range 350 to 800 nm to electrical input power in watts expressed in μmol/sec/W.

**PPFD:** Photosynthetic Photon Flux Density – Flux per unit area expressed in μmol/sec/m^{2}.

**Lumens to μmol/sec conversion factor:** Multiply flux in lumens by this factor to convert to PPF in units of μmol/sec. This conversion factor can also be used to convert illuminance in lux to photosynthetic photon flux density (PPFD).

To convert from footcandles to PPFD first convert the illuminance in fc to lux by multiplying by 10.7639 lux/fc and then use the lumens to μmol/sec conversion factor.

Note: This factor applies to the measured spectral distribution only and cannot be applied to other light sources.

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