The answer to this question has to do with the fact that both light and sound are made up of waves. However, the waves which make up sound are quite long - each wave is a foot long, about the same length as waves you might see in the water at the beach (the length of a wave is called its wavelength ). On the other hand, the waves which make up the light we see are much, much smaller - about a million times smaller. They are about as small as the smallest thing you can see under a very good microscope. Now it happens that one of the things about waves is the following: if they encounter an obstacle which is smaller than their wavelength, the wave just kind of wraps around the object and keeps on going. This is why you can hide behind a big tree trunk and the voices of people on the other side of the tree will still reach you (because the long waves of the sound wrap around the tree), but light from their flash light won't (because the short waves of the light can't wrap around such a big object). Sound and light act similarly when they reach a corner of a house - the sound waves are long and kind of wrap around the corner and then spread out from there, where as the very short light waves can't bend around the corner. As you might have guessed already, this means that light does wrap around very small things (things smaller than a millionth of a foot), and does bend a tiny tiny bit around corners, but mostly this is so small it is impossible to see with your eye.

All waves exhibit similar properties, and both light and sound are types of waves (although, technically, light is a transverse wave and sound is a longitudinal wave). One feature of waves, known as diffraction, is that they can bend around corners or obstacles. The degree of diffraction increases with increasing wavelength. Furthermore, the size of the obstacle(or opening it is passing through) must be comparable to or smaller than the wavelength of the waves. If the wavelength is much smaller than the obstacle (opening), there will not be much, if any, diffraction. Since the wavelength of visible light is on the order of 0.5 microns, or 0.0005 mm, light will only diffract when going through very narrow openings. Sound waves, on the other hand, have a wavelength on the order of 1 meter and diffract very easily. This allows sound waves to bend around corners.