Ok, take a deep breath… here we go:
Visible light is a specific frequency set of electromagnetic radiation measuring between 400 and 700 nanometers in the Electromagnetic Spectrum (4.00 × 10−7 to 7.00 × 10−7). This range sits between the infrared and ultraviolet wavelengths.
Whew! what does that mean? And more importantly how does it relate to photography? Well, even a basic understanding of the way light works can lead to dramatically improved images. Light and its characteristics are commonly downplayed especially in a classroom situation because the descriptions tend to be seen as “techy” and not important. This week we embark on an introductory tour of light and how it relates to your images. I promise to only get as technical as I have to in order to cover the basics.
In photography, Visible Light has four attributes that we are concerned with, Quantity, Quality, Color and Direction. This week we will focus primarily on quantity of light. When preparing to take a photograph, one of the first things I consider is quantity or intensity of light in my subject. This is true whether you are taking a photo of a person or a mountainside. An easy way to think about the way light intensity works is to think about the last time you went to the movies. When you entered the dark theater, things were dark or underexposed. If you were to take a photo in the dark theatre, you would have to increase your ISO, slow your shutter speed or move to a larger aperture, this would increase the light hitting your sensor when you take the photo. Conversely, after the movie was over you walked outside and the sun was blaring bright and everything was overexposed. In this situation you would have to decrease your ISO, increase your shutter or move to a smaller (higher number) aperture. All of these would decrease the amount of light that is introduced to your sensor. Make sense? Let’s move on.
If you have ever watched a video tutorial on lighting, someone will invariably mention the inverse square law when they are talking about lighting. What is this law and how does it relate to photography? In technical terms, illumination force changes in inverse proportion to the square of the distance from the source. Or, when you move a light farther from your subject it gets darker faster than you would expect. This is all related to the intensity of the light on your subject. Measuring this amount of light is done with that light meter that you bought and stuffed in your bag and never use. To make things easy, let’s put the technical measurements including the light power aside for the moment and consider a light pointed at your subject in your home studio. The light is 1 meter from your subject and the light falling on your subject measures a reading of 4. I realize this is not the proper way to denote the measurement of light on a subject, I am purely using this measurement for illustration. My initial thought, when I was learning lighting was that if I double the distance that my light would be cut in half, this is wrong and where the inverse square law comes into play. If you take the measurements of a light measuring a 4 at 1 meter, the light falling on your subject at 2 meters is actually 1 not 4. What this means is that the amount of light falling on your subject will be ¼ of what would think it was going to be when you doubled the distance. This was one of the roughest things for me to grasp when I first started. Once this concept sank in for me, it was one of the biggest AH-HA moments when I was learning studio photography.
In practice, what this means is that when moving lights around your shooting environment, it should be done in small amounts. When I am photographing a subject I am moving the lights inches at a time, not large sweeping movements. This is especially noticeable when taking pictures of small objects with the lights close to the subject. I found a small tape measure invaluable in learning this theory, it helped me to solidify in my head that if I was metering a 4 at 1 meter, I would move it half a meter and have half the light.
Here are a few example images illustrating the inverse square law. It should be noted that this is not sponsored by Contadina, this was just the first can I grabbed out of the pantry when I was setting up for example images. As you can see the first image is overly bright, lacking in contrast and has dulled colors. The light is also wrapping around the front of the can way too much for what would be considered a good product shot. The light source was 1 foot away from the subject The second shot I moved the light source so that it was 2 feet from the subject. The subject is significantly underexposed and the image lacks contrast and has dull colors. This third image is much closer to what I would consider proper color and contrast. The light source for this shot was 18 inches from the subject (12 original inches plus 6 more).
There you have it, the first property of light demystified. Check back next week for my discussion on Quality of light.
Get out there and take some pictures!