According to what my teacher at school taught me, light can be diffracted just like any other wave. A friend of mine, however, says that light doesn't diffract, and that it reflects so that it seems as though it is diffracting.
He pointed me toward a certain experiment using a pinhole in paper and a source of light in a dark room, saying that it proves light doesn't diffract.
I, since my friend's explanation of the experiment was very rudimentary, am looking for a final say in the matter. Can light be diffracted (normal speeds, no medium change)?