PAR vs PUR measurement of light, efficency
This is a new thread to discuss the differences in terms of growth, asethetics and brands of various bulbs of using PAR and PUR measurements.
Some background is useful as these terms are not as familiar to many hobbyists:
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.
I remain unconvinced.
http://www.new.aslo.org/lo/toc/vol_31/issue_3/0557.pdf
Show me some quantum yeld differences, Relative growth rates differences between PAR and PUR with typical bulbs.
Something.
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.
