Of course we receive less sunlight in winter, because the sun is lower in the sky, so the light has to travel through more atmosphere, and loses strength. Does this mean that the blue light is more scattered out?
Are the frequencies we receive in the winter relatively the same as in summer or is there a change in the received spectrum? Are there less UV-B rays in winter than there are in summer relative to UV-A? If so what is the cause of that?