The ray that gets through the pinhole determines the position of the image. While there are rays of light emanating from each point on the light bulbs, for simplicity, only those rays which get through the pinhole have been drawn. The ray model shows that the light rays from each bulb cross as they go through the pinhole producing reversed images on the screen. Finally, look at an extended light source, such as a long fluorescent tube or an object. In Figure 3, the extended light source is represented by an arrow.
Light rays go out in all directions from every point on the arrow.
To illustrate how images are reversed we have simplified this drawing to show only three of the light rays passing through the pinhole. The light from the middle of the arrow goes through the pinhole and hits the screen in the middle. The light from the bottom tail of the arrow goes through the pinhole and hits the screen on the top. The image on the screen is therefore, reversed. Footnotes about Key Conceptual Points 1.