David K. Lync, Bernard H. Soffer

The solar spectrum peaks in the green part of the spectrum, right? Wrong! It only peaks in the green when plotted in wavelength units. It peaks in the nearinfrared when plotted in frequency units.
Many people believe that the solar spectrum and the color sensitivity of the eye both peak at around 0.5 μm (500 nm) in the green. The notion is sometimes stated even more strongly, i.e., that evolution has produced a human eye whose color sensitivity has been optimized to match the solar emission spectrum. But this apparent wavelength coincidence between the solar spectrum and the eyes’ sensitivity is an artifact resulting from the units in which the solar spectrum is plotted. Comparing irradiance to sensitivity is like comparing apples to oranges: they are fundamentally different quantities and their shapes and peaks should not be likened to one another although they can legitimately be multiplied together.