On a sunny day, notably in Winter, your hand can feel warmth from the Sun, but as soon as you step out of the Sun your hand feels cold. This suggests that the effect is radiant energy from the Sun. That's all rather trite. But is the radiant energy that makes you feel warm actually mostly due to absorption of visible light and UV (ultraviolet) and less due to IR (infrared)? Referring to a spectrum of incident solar radiation at ground, such as here in fig 2.5 http://www-paoc.mit.edu/labweb/notes/chap2.pdf . As the intensity of solar radiation peaks in the visible, and the lower part of the IR band is heavily attenuated. It seems to me that the warming is not IR direct from the Sun, but visible and UV being absobed and causing heating. Regards, CobblyWorlds.