How to Calculate Contrast Ratios for More Professional Lighting Setups

Whether you are an avid film watcher or someone who just likes to binge watch the latest TV sitcom, there is something that each of these forms of entertainment have that a good video producer or cinematographer should understand to help better create engaging shots that develop the emotion on screen and set the tone of a project...that is a proper contrast ratio.

To understand contrast ratio or lighting ratio, you need to pay attention to the way your favorite TV shows and films are lit. In most cases, the elements of lighting disappear into the background. Unless you’re truly paying attention or have a trained eye, you might not notice the nuances of lighting, but the lighting is an integral part of the story and helps affect the emotions you feel as a viewer.

What is a contrast ratio?

Contrast ratio refers to the comparison of the intensity main source of light from which shadows fall, to the light that fills in the shadow areas. Another way to approach this is that contrast ratio is the difference in the bright areas of a scene compared to the darker shadow areas. As you watch your favorite sitcom or cinematic entertainment, pay attention to how the characters are lit.

Contrast ratio is important as it helps tell the story by developing a mood, be it dramatic or light-hearted. For example, a low contrast ratio like 1:1 or 2:1 is best set for TV comedies and interviewing purposes where the subjects should be evenly lit to give a feeling of openness and enlightenment. On the other hand, a high contrast ratio like 4:1 or more creates more shadowy areas that give the scene more drama and a sense of foreboding. High contrast ratios are best used in film noir or thriller type films where dark shadows add to the sense of mystery and suspense.

The main advantage in using and documenting a contrast ratio across shots is that it allows you to maintain the same intensity in the brightest and darkest areas of the face to keep the shots consistent throughout the project.

Measuring Contrast

To measure the contrast ratio you will need a light meter. The process starts with you measuring the main source of light, or the key light. Get a reading from the brightest area on the face of your subject. Then, measure the area lit by the secondary light, or fill light. To make sense of what you have just measured you have to understand that the information you have just gathered is in F-stops, a measure of light. With each additional F-stop, for example going one stop from f/1.4 to  f/2.0, you create a doubling of light. The reverse is also true; moving one stop from f/8.0 to f/5.6 results in a halving of the light.

Let’s say you grabbed a measurement from your key light of f/8.0. Then, when you measured your fill light area, you get a reading of f/4.0. This will lead you to a contrast ratio of 4:1 because there are two stops between f/4.0 and f/8.0 and each stop doubles the amount of light. In other words, two stops x twice the light per stop = four times as much light at f/8.0 than at f/4.0.

If you get a measurement from your key light of f/8.0, then a reading of f/4.0 from your fill light, you will have a contrast ratio of 4:1 because there are two stops between f/4.0 and f/8.0 and each stop doubles the amount of light
If you get a measurement from your key light of f/8.0, then a reading of f/4.0 from your fill light, you will have a contrast ratio of 4:1 because there are two stops between f/4.0 and f/8.0 and each stop doubles the amount of light

Gathering this type of this type of information is important because it keeps continuity in the lighting from shot to shot throughout a project. Furthermore, if a contrast ratio is established on a project, the cinematographer and gaffer crew can better work ahead of the director and the talent during down times to set up scenes ahead of schedule, knowing what the lighting setup will be.

Summary

To recap, contrast ratio is the difference in the bright and dark areas of a scene cast from the key light compared to the fill light. To measure this ratio one will use a light meter and the ratio will be calculated in F-stops. Each stop moving up or down the range will create a doubling or halving of light. In the end the ratio will be expressed in a set of numbers or ratio like 8:1, 4:1 or 2:1. This process of measuring the light can help create consistency in shot to shot throughout a project as well as help make the crews set-up more fluid during down time. Ultimately, using the right contrast ratio helps to add the drama or lighten mood as needed in the script.

Marc Johnson is a University of Chico graduate, a lover of the creative arts, and an avid photographer, with an undying entrepreneurial spirit.

6 COMMENTS

  1. I really liked your article about lighting contrast ratios, which is a topic that few people seem to know or understand, yet is extremely useful when figuring out the lighting style of your interview picture. This technique is most common when lighting actors in dramatic scenes, but it is also useful for lighting serious documentary interview subjects. In fact, I always teach this technique in my own documentary production classes. It helps people better understand how they can control the light and the look of their interview. Yet, there are a few things that I might add to your great article.

    Instead of using F-stops for calibration, I would try using foot-candles, which is an easier and more precise way to compute the actual lighting ratio. However, you must measure the fill and key lights separately because there is a lighting overlap on the face and by measuring them separately you can get the precise value for each. You measure with the lightmeter next to the face pointed at the light source.

    The computation is done by measuring the key light alone and then measuring the fill light alone and adding these foot-candles measurments together. To get the lighting ratio you divide the fill light measurement into the sum of the key and fill light measurements together.

    For example, you measure the fill light at 40 foot-candles. You then measure the key light at 320 foot-candles. You then add these two figures together, which equals 360 foot-candles. The ratio is obtained by simply dividing the fill light foot-candles (40) into the sum of the fill and key light together (360), which is 9 (40÷360=9). So, our exact lighting ratio is 9:1, which would render a very nice film noir, dramatic look to your interview subject, indeed.
    Brian Patrick, Professor, Film & Media Arts Dept., University of Utah

  2. Correct me if I’m wrong, but it seems like you’re getting the wrong contrast ratio? If you’re measuring the fill at f/4, and let’s say that’s 20 foot candle, then you’re key at f/8 would be 80 foot candle. Contrast ratio is determined by key+fill:fill. So, in this case (80+20)/20 = 5. The contrast ratio in the scenario suggested in this article ought be 5:1, not 4:1.

  3. There is a lot to say about lighting, and in the end video is all about lighting and sound. I wish videomaker writes more articles about lightning. I think good lightning is more important than the bitrate of a camera.

    • Bill, thanks for the feedback. We have a new episode of the Videomaker Podcast going up on 6/29 where we talk about lighting, be sure to check it out!

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