Optics
The science of making light go where we want it to is called optics.

The simplest optical phenomenon is a shadow, in which some of the rays of light are blocked by an object. We get big shadows if the object is much closer to the light source than it is to the wall where the shadow appears.



 


We get sharp shadows if the light source is small compared to the other distances involved.



Light from the bottom of the bulb can reach different parts of the screen than can light from the top of the bulb. The places where some of the light can reach and some cannot are the fuzzy edge of the shadow.

How does this work with real bulbs? Here's an example

Check me:
Shadows are three-dimensional