This is from Planted Tank > a site about Coral reefs. It pretty much explains PAR and PUR
Photosynthetically available radiation (PAR) is defined as the amount of radiant energy available within the approximate spectral range of 350 to 750 nm (Tyler 1966). Instruments commonly used in studies of photosynthesis are PAR meters; that is, they report 400J700 I,h) or total PAR. Photosynthetically usable radiation (PUR) is defined as
the fraction of photosynthetically available radiant
energy of such wavelengths that it can be absorbed by
the algal and plant pigments. Light is selectively absorbed
by most algae in the blue and red regions of the
spectrum, causing the transmitted light to be concentrated
in regions of the spectrum where algal pigment
systems are ineffective at trapping light for photosynthesis
(Sullivan et al. 1984). PUR is necessarily less than
PAR, and PUR will depend on both the
pigment complement
of the microalgae and the spectral composition
of the
available submersed radiant energy.
It has been suggested that we can calculate PUR through a light calculator and thus have a more precise method of measuring light than PAR. However, I have argued that without knowing the pigment complement of the plants in question, none of which are known............nor have been quantified near as I can tell, maybe I have not searched enough yet, you cannot say much about it. Research also supports this view.
PAR will always be equal to or higher than PUR.
I do not dispute that. PAR meters are also easy to measure with, the methods for measuring specific PUR wavelengths and intensities is not.
Modeling calulators can and do have issues, and need results to verify.
I'm asking and debating whether it can be measured and verified in the aquarium to the same argument made by PUR calculator proponents. There is not enough evidence to say that there is at this point.
You can speculate without support, but you cannot say much else.
What I am asking and looking for is some meat on the bone here, some real support that it makes a difference that aquarists can see, measure, quanatify, heck, anything other than "belief" and yes, I "feel good".
Here's an algal back ground paper that discusses what is involved and the methods to measure PUR in situ, a much higher bar than using a PAR meter. Given that most bulbs used already have a good amount of Red and blue anyway, this starts to get pretty insignificant and difficult to test and support any differences using PUR vs PAR for aquarium plants.
http://www.new.aslo.org/lo/toc/vol_31/issue_3/0557.pdf
Are comparison of modesl is detailed here:
http://222.aslo.org/lo/toc/vol_44/issue_7/1599.pdf
While there was a difference between PAR and PUR models in biomass, look at the variation, it's quite a bit. Adding 300 species of plants and that would go even higher. There was good correlation with the PAR model and production, see the last Figure 9, also, look at table 1.
Add less light difference and general good PAR/PUR ratio to begin with with FL lights, we have less differences. I've supported my view, time to support yours. Show me something that suggest what is claimed with PUR really helping anyone with any aquatic plant using typical lighting used in the hobby vs PAR. You may use google, any resources available that you might have to show this.
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the Einstein is a good indicator of the photosynthetic activity of plants. The biological mechanisms in place during the luminous phase of photosynthesis do not depend on the photons' energy, but on their number. This is exactly what the Einstein displays. The PAR (Photosynthetic Available Radiation, unit µE/m2/s) measures the number of photons reaching a surface, all this in the wavelengths of the visible light (between 400 and 700nm). It is indeed in this portion of the spectrum that we can find the different absorption peaks of the photosynthetic pigments. As these pigments do not absorb energy in a equal manner on all that 400-700nm range, but only at certain precise wavelengths, some prefer using the PUR (Photosynthetic Usable Radiation) in order to quantify the number of photons truly used by the photosynthetic cells. The PUR is thus defined by the light source (emitted spectrum, intensity) and by the studied pigments (because of their absorption spectrum).
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The Importance of the PAR/PUR of Your Reef Lights
Phototropic Response of Photosynthetic zooxanthellae in corals
Can't figure out why your
clams,
anemones and
corals aren't really growing? You have a ton of lights hanging over your tank with plenty of watts per gallon, but everything just sort of sits there in your tank. Spend a few minutes to learn about the PAR/PUR of your reef tank lighting and you will quickly see what your problem may be. It's not so much how much light you have as what kind of light you have.
PAR, or Photosynthetically Active Radiation 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.
PUR, or Photosynthetically Usable Radiation is that fraction of PAR that is absorbed by zooxanthellae photopigments thereby stimulating photosynthesis.
Photosynthetic zooxanthellae in corals and some other marine invertebrates utilize light in the 400 to 700nm range in different ways. The following from the
Aquarium Lighting article on the
American Aquarium; Aquatic Information, Products site relates to the graphic above:
"
Important Definitions as it applies PAR in plants and zooanthellic algae: See the graph above as it corresponds to each of these definitions.
*A: Phototropic response; having a tendency to move in response to light. Basically this is the Chlorophyll containing plant or algae "moving" to respond to a positive light source to begin the process of photosynthesis (initial growth of plants, zooxanthellae, etc.).
*B: Photosynthetic response; the process which begins when energy from light is absorbed by proteins called photosynthetic reaction centers that contain chlorophylls.
*C: Chlorophyll synthesis is the chemical reactions and pathways by the plant hormone cytokinin soon after exposure to the correct Nanometers wave length (about 670 NM) of light resulting in the formation of chlorophyll, resulting in continued growth of a plant, algae, zooxanthellae and the ability to "feed" and propagate, and without this aspect PAR (670 NM light energy), zooxanthellae and plants cannot properly "feed" propagate. The results of the lack of this high PAR "spike" would be stunted freshwater plant growth, and eventually poor coral health in reef tanks."
As you can see, a light source which provides light in all three of these zones (A, B and C) is important for coral growth and health.
Fluorescent Light Bulb Spectrums
Different fluorescent (and Compact Fluorescent, MH, LED) bulbs provide more or less light in different areas of the spectral range. Examining the spectral ranges of bulbs before you buy will help you get the effect that works best for your situation. For example, if you like the Coralife 20,000K for its mid and upper (B & C)spectral range, but it doesn't have enough light in the actinic range (A), you could add the UV Actinic to get the effect that you need. Mix and match until you get exactly what you want.
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http://www.defblog.se/LightCalculator/
and ill say this for them, they do grow danker bud than hps, bit more potent, but lot more aroma.
