2022-03-10
Horticulture specific metrics PPF PPFD are appropriate metrics when comparing different Horticulture Lamps. These cover the entire range of light that is used by plants for photosynthesis.
Metric for General Lighting | Metric for Horticulture |
Lumens | PPF |
LUX | PPFD |
Lumens/Watt | PPF/W |
Photosynthetically Active Radiation is the spectral range (wave band) of light radiation from 400nm to 700nm wavelength. Photosynthetic organisms use light within this range for the process of photosynthesis. PAR is a range of wavelengths and is not a metric with any units.
PPF (Photosynthetic Photon Flux)
PPFD is a measurement of the amount of Photosynthetic Photon Flux per unit area. It number of photosynthetically active photons that fall on a given surface each second”. PPFD is measured at a specific position of plant canopy and is measured in micro moles per square meter per second or μmol/m2/s. This metric is commonly used in PPFD Charts like below.
Daily light integral (DLI) describes the number of photosynthetically active photons that are delivered to a specific area over a day. PPFD gives us the intensity your plants are receiving per square meter per second. DLI gives us the intensity your plants are receiving per square meter per day. DLI with a lamp running 12 hours a day is exactly half of lamp running 24 hours a day. Similarly DLI with a lamp running 12 hours a day is 50% less than a lamp running 18 hours a day.
PPF/W is one of the most important metrics for efficiency of a light source. It is the total PPF produced by each watt of electrical power consumed. It is also same as micro moles per joules of energy used. While comparing PPF/W for different lamps it is important to ensure PPF/W number is calculated at system level since some electrical power is lost in power supply losses and electrical wires/traces.
PPF/Watt is same as μmol/j
1 Watts =1.00 J/s ( joule per second )
PPF = μmol/s ( micro moles per second )
PPF, PPFD, PPF/W metrics measure only photons within the PAR range. These metrics are limited to PAR range, however there are well known benefits of light outside PAR range. Also these metrics do not account for quality of light spectrum. It is important to look at spectrum along with these metrics for a complete picture.
A full spectrum lamp at 2.5 PPF/W will greatly outperform a 3 PPF/W lamp that has only only Red + Blue photons