Adding digitized data from one LED manufacturer's white LED SPD curves, we can arrive at the following table of PPFD Conversion Factors, for converting illuminance in kilolux to PPFD in μmol/s-m 2:Ģ700K white light LED (Philips Luxeon Rebel LXW9-PW27)ģ000K white light LED (Philips Luxeon Rebel LXW9-PW30)ģ500K white light LED (Philips Luxeon Rebel LXW7-PW35)Ĥ000K white light LED (Philips Luxeon Rebel LXW8-PW40)ĥ000K white light LED (Philips Luxeon Rebel LXW8-PW50) One source is CIE 15:4, Colorimetry (2004). SPD graphs are relatively easy to come by, but finding the same information in tabular form, needed for the above equations, is more difficult. Given an illuminance value (lux or footcandles), we can similarly calculate the photosynthetic photon flux density (PPFD) in micromoles per second per square meter (μmol/s-m 2) for the given light source. Summing over the range of 400-700 nm yields the photosynthetic photon flux (PPF) per lumen for the given light source: H = Planck's constant (6.626 x 10 -34 joule-seconds) With this, the photosynthetic photon flux (PPF) per nanometer in micromoles per second per nanometer can be calculated: Where W rel(λ) is the relative spectral power distribution and V(λ) is the luminous efficiency function at wavelength λ. Given the CIE 1931 luminous efficiency function V(λ), we can calculate the spectral radiant flux Φ(λ) for plants in watts per nanometer for each lumen as: One watt of radiant power at 555 nm is by definition equal to 683 lumens. Based on its SPD, a light source will have a conversion factor that can be used to translate luminous flux density (illuminance) received by the plant into photosynthetic photon flux density (PPFD), in μmol/s-m 2. If the spectral power distribution (SPD) of a light source is known across the relevant wavelengths (400-700 nm), then the amount of photosynthetic energy available to plants can be determined. The mathematical basis for the calculation of PPFD: PPFD is not available as a Statistical Area metric, but it is available in the Schedules, Isolines, and Highlight Values commands.
Flux density calculator full#
PPFD can only be calculated with the Full Radiosity calculation method. (See Procedures tab for specifics.)ĪGi32 assumes that all sources contributing to the calculation grid have the same PPFD Factor, as selected in the PPFD Conversion Factors dialog. In AGi32, PPFD is selected as the calculation type rather than as a light source characteristic.
As with human vision, plants are more likely to respond to (absorb) light in some wavelengths than others. However, not all wavelengths have an equal likelihood of being absorbed, as determined by the various plant pigments that might be present. Any photons within this spectrum that are absorbed by the plant will contribute to photosynthesis. This is the range that stimulates photosynthesis.
The spectrum to which plants are most sensitive varies with the species, but for most plants the spectrum is very similar to the visual spectrum to which humans are sensitive, approximately 400-700 nm. Micromoles per second per sq.meter (μmol/s-m 2) Photosynthetic Photon Flux Density (PPFD) Light energy for plants, on the other hand, is measured as photosynthetic active radiation (PAR), with light falling onto a surface measured as photosynthetic photon flux density (PPFD) with units of μmol/s-m 2. Light energy for humans is measured in lumens, with light falling onto a surface measured as illuminance with units of lux (lumens per square meter) or footcandles (lumens per square foot). Lighting for plants is different from lighting for humans. Photosynthetic Photon Flux Density (PPFD) - Concepts
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