[BasilG]

I think a large part of the problem is not just the visible wavelengths from the sun, but also the IR, and to a lesser extent the UV. UV is less of a problem since most glass absorbs a fair amount of it anyway. IR contains a lot of the energy, and you need to ideally remove it before it gets into the lens. 

 

 


IR photons contain less energy than those in the visible spectrum (E = hf = hc/λ where E is energy, h is Planck's constant, f is the frequency, c is speed of light, λ is wavelength). So I'd be surprised if that were of any worry, but am open to explanations as to why I am mistaken.