One of the assumptions that engelmann made was that the sun (his light source) emits equal numbers of photons at each wavelength in the visible spectrum. in reality, the sun's emission peaks in the yellow region of the spectrum, with relatively fewer photons emitted in the red and violet-blue regions.
recall that the action spectrum from engelmann's experiment plotted the rate of photosynthesis (as measured by oxygen production) versus wavelength. in each of the following graphs, the black line shows engelmann's original action spectrum deduced from the distribution of aerotactic bacteria around the alga.
which red line shows the same action spectrum corrected for the unequal number of photons emitted across the visible spectrum?