That might be more of a problem in the higher latitudes, but on Martian equator, sunlight at noon will be comparable to sunlight at noon somewhere around the Baltic Sea - still perfectly fine. Also, Martian atmosphere is thinner and blocks less light than ours. (Unfortunately it also does not prevent harmful UV rays from reaching the surface.)

One possible problem not discussed would be the giant dust storms that can cover large tracts of the planet for weeks. We don't have this kind of weather on our cradle planet.