What Causes Shadows?
Where anything through which rays of light cannot pass intercepts the light rays coming from a luminous body, the light rays are turned back in the direction from which they come and the part on the other side of the object which intercepted the light goes into shade and a shadow results. A shadow then is produced by cutting off one or more light rays. We notice shadows when the sun is bright in the daytime and at night when we walk along the streets lighted partly by street lamps. The shadows we see in the daytime are caused by our cutting off and throwing back some of the light rays which come from the sun. These are not so dark as the shadows we see at night because the rays of light from the sun are so bright and are reflected from so many other objects to the side and in back of us.
When, however, we are walking along a dimly lighted street and come to a street lamp the shadows our bodies cause are quite black. The night shadows are darker because the source of light is less intense and the objects to the side of and in back of us (if we are walking toward the light) do not reflect so much of the light rays as they do of the sun’s rays in the daytime.