Lighting: physics of light

Rainbow
Rainbow

Inspired by Light: Science and Magic by Hunter, Biver, and Fuqua I would like to discuss the fundamentals of lighting in the series Understanding Lighting: from physics to moods. Lighting deals with light, subject, and viewer. We discuss all three of them.
Essential characteristics of light (sources) are:

  • Brightness It makes quite a difference if we have to take a picture with only the moon shining instead of the sun. In general, the more light the better the quality of the pictures is. It is much easier to deal with too much light (almost closed Aperture and a very fast Shutter Speed), than too little light (the quality decreases substantially in the high ISO range). Also, light loses its brightness if it travels a long distant (look at the sky when it is dark, all of these starts are more powerful than our sun, however, we only see a tiny twinkle of each of them).
  • Color Normal light consists of light with different wave lengths. We see that when the sun shines during the rain: the rainbow. With the right mix of these colors it looks white. If this white light reflex on a red wall it reflects only red light. The way we see light is an interpretation of our brains of what we see. For example, we know that snow is white; although in a picture it may look gray we “see” it as white. A camera is not always able to do this intelligent interpretation of light. So, sometimes we have to help it by setting the White Balance to the right color temperature.
  • Size of the source On sunny days with a blue sky the shadows are harsh. On cloudy days there are hardly any shadows. In the first case we have a very small light source and in the latter a very large one, resulting in, respectively, direct and diffuse light.

Reflections on a subject play an important role in photography, because in a sense they create new light sources with their own characteristics. For example, a reflection on a non-glossy subject like a matte wall causes a diffuse reflection (reduction in brightness). As mentioned above, if light reflects on a red subject, it reflects only red light and absorbs all other colors (change of color). Also, if the light reflects on a (small) mirror-like subject, it creates a (tiny) light source producing harsh shadows; this is called direct reflection (change of size of light source).
The viewer is of course our camera. When we shoot outdoors and when we are not happy with the position of the light source, the sun, the only remedy is to change the position of the camera. In a studio, however, we have the additional possibility to change the position of the light source(s). Also, we can use soft boxes instead of waiting for the clouds. Furthermore, we can use reflectors, “producing” warm of cold light, to light the subject from different angles.
So, now that we know more about light, the next step is lighting setups. This is the topic of the next blog.