To photographers, the important principles of light are those that predict how it will behave.

that strikes it: it can transmit, absorb, or reflect that photon.

For single light sources, the size of that source is the primary factor influencing its contrast. A small light source is always a hard light source, and most large sources are soft ones. We see that the sun in Figure 2.4 occupies little area in the diagram, so it is a small light source. The cloud covers a greater area in Figure 2.6, making it a

direct transmission, in which light passes through a material in a predictable path.

Unlike the field around the magnet, however, the electromagnetic field around the photon is not constant in strength. Instead, it fluctuates as the photon travels. If we could see this change in the strength of the field it would look something like Figure 2.1.

2.7 A shadow so soft that much of it is just barely visible is the result of a very large light source.

Notice that the strength of the field moves from zero to its maximum-positive strengths and then back to zero; it then repeats the pattern in the negative direction. This is why the field around a beam of light does not attract metal like an iron magnet does. The field around a photon of light is positive half of the time and negative the rest of

Reflection

photographic lighting.