Talk:Photosynthetically active radiation

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Photosynthetically useful wavelengths[edit]

This article states that leaves are green because light at wavelengths >= that of green light does not carry enough energy for photosynthesis and because plants reflect, rather than absorb, the useless wavelengths. The article then goes on to state that red light is one of the most important for plants. This contradicts the earlier statement since red light has the longest wavelength of any color in the visible spectrum.

The conflicting statements from the article:

  • Photons at longer wavelengths do not carry enough energy to allow photosynthesis to take place, and plants have developed, through billions of years of evolution, the capacity to scatter these photons away, hence the very high reflectance and transmittance of live green leaves.
  • Chlorophyll, the most abundant plant pigment, is most efficient in capturing red and blue light. Horticulturists say that blue light is the most important for leaf growth and that red light encourages flowering.

PHaze 23:27, 2 July 2007 (UTC)

Just plants?[edit]

I would think that PAR should refer to any wavelengths that organisms are able to use to photosynthesise and not just wavelengths that plants use. Currently the article states that organisms other than plants use near-infrared to photosynthesise - this must also be PAR. Shall I change it or is there a reason for the distinction? Smartse (talk) 15:28, 13 April 2009 (UTC)

Any photosynthesizing organism[edit]

I agree. The article even speaks of "spectral range of solar light from 400 to 700 nanometers that is useful to terrestrial plants". This is a mistake. Cyanobacteria (these are bacteria, not plants, and they mostly occur in water) also have PAR. From John T.O. Kirk (1983) "Light and photosynthesis in aquatic ecosystems", Cambridge University Press, Cambridge, page 26:

"Photosynthetically available radiation (commonly abbreviated to PAR), 400-700 nm, [...]"

Kirk's book is about the aquatic environment. Note that here the abbreviation stands for something slightly different.

Another nice text involving PAR and aquatic organisms that are not plants:

Please change the text, Smartse.

OpenScience (talk) 15:28, 20 April 2009 (UTC)

Conversion unit between energy PAR and photon PAR 3000K (warm white) LED[edit]

The following was on my Talk page: I saw you edited the LED with 3000k warm white can convert the energy PAR to the photon PAR multiply by 4.98. Could you send me a link of concerned paper or documents relate to this issue? Which could show the 3000K warm white unit converted by the 4.98 µmol s-1W*-1 I am looking forward for that papers or documents as necessary for research working. Zhangfan0612 (talk) 11:22, 2 January 2014 (UTC)

Unfortunately I do not have such documentation. It follows directly from the definition of PAR and the black-body Planck curve, as in the equations in the article. Please note that the article also states: For artificial light sources, that usually do not have a black-body spectrum, these conversion factors are only approximate.. In other words, the conversion factor does not apply exactly for an LED light source.
If you enable email in your Wikipedia preferences, I can email you the python script that I used to calculate the conversion factors.
Han-Kwang (t) 12:06, 2 January 2014 (UTC)

could you send me the python script? by fan0612 Wikipedia preference(I lost the password of zhangfan0612) or by my e-mail [deleted] thanks you so much — Preceding unsigned comment added by Fan0612 (talkcontribs) 06:15, 3 January 2014 (UTC)

See your email. Han-Kwang (t) 12:03, 5 January 2014 (UTC)


Can someone include mention of PBAR (Plant Biologically Active Radiation) in the article? I don't know where or when the term originated, but this an example of an article that mentions it: . I've also seen it in presentations and terminology pages in horticulture. After that, it can be added to the Pbar disambiguation page. --Zom-B (talk) 09:30, 6 December 2017 (UTC)