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Industry News >> Whats the PAR ??
What is P.A.R. or Photosynthetically Active Radiation?
Photosynthetically active radiation, often abbreviated PAR, designates the spectral range (wave band) of solar radiation from 400 to 700 nanometers that photosynthetic organisms are able to use in the process of photosynthesis.
This spectral region corresponds more or less with the range of light visible to the human eye. 
Photons at shorter wavelengths tend to be so energetic that they can be damaging to cells and tissues, 
but are mostly filtered out by the ozone layer in thestratosphere.
Photons at longer wavelengths do not carry enough energy to allow photosynthesis to take place.
Other living organisms, such as green bacteria,purple bacteria and Heliobacteria, can exploit solar light in slightly
extended spectral regions, such as the near-infrared. 
These bacteria live in environments such as the bottom of stagnant ponds, sediment and ocean depths.
Because of their pigments, they form colorful mats of green, red and purple.
Typical PAR action spectrum, shown beside absorption spectra for chlorophyll-A, chlorophyll-B, and carotenoids Chlorophyll, the most abundant plant pigment, is most efficient in capturing red and blue light.
Accessory pigments such as carotenes and xanthophylls harvest some green light and pass it on to the photosynthetic process, but enough of the green wavelengths are reflected to give leaves their characteristic color. 
An exception to the predominance of chlorophyll is autumn, when chlorophyll is degraded (because it contains N and Mg) but the accessory pigments are not (because they only contain C, H and O) and remain in the leaf producing red, yellow and orange leaves.
PAR measurement is used in agriculture, forestry and oceanography.
One of the requirements for productive farmland is adequate PAR, so PAR is used to evaluate agricultural investment potential.
PAR sensors stationed at various levels of the forest canopy measure the pattern of PAR availability and utilization. Photosynthetic rate and related parameters can be measured non-destructively using a photosynthesis system, 
and these instruments measure PAR and sometimes control PAR at set intensities.
PAR measurements are also used to calculate the euphotic depth in the ocean.
Wikipedia.com
As noted above, PAR is one way of measuring light that places more importance on specific wavelengths
that are useful in powering photosynthesis.
Another common but less accurate measurement of the quality of light put out by a light source is luminous flux, given in units of lumens or lux.
We address lumens and why they aren’t relevant when assessing the quality of a light source for growing plants in the article found here above.
This means that two lights can have the same lumen rating but one could have a significantly higher PAR rating 
if it uses more of the wavelengths used during the process of photosynthesis.



 

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