Re: How can the reducing powers of different photosynthetic pigments be tested?

I think you'd need to see how photosynthesis depends on the wavelength 
of light used.

You could try this with whole leaves, or whole plants, which I think 
would be quite simple, or you could do some very tricky isolation of 
the chloroplasts and monitor their activity.

The response of photosynthesis to light of various wavelngths is called 
the photosynthetic action spectrum.

Action spectrum diagram http://www.rrz.uni-
hamburg.de/biologie/b_online/e24/2.htm

Another version of the spectrum is here: http://www.rrz.uni-
hamburg.de/biologie/b_online/e24/24.htm
The discussion is more detailed, though; but there's much history as 
well.

Notes on the general topic http://www.sprl.umich.edu/GCL/Notes-1999-
Fall/respir_photosyn.html

Some investigations are noted at the end of this bulletin. It might be 
worth getting in touch with the authors. http://w
ww.pkal.org/faculty/f21/pubs/thisweek/01_25_00.html

A practical experiment, but nothing about how to get chloroplasts for it: 
http://www.msu.ed
u/course/lbs/145/luckie/Lab3.html

This is not quite an answer to your question! It's terribly tricky to 
isolate photosynthetic systems so I don't recommend trying to separate the 
different pigments. Without chlorophyll, photosynthesis will not work at 
all so the effect of the accessory pigments will always be superimposed on 
the underlying chlorophyll processes.

Ewen McLaughlin