Directing Mood with Lighting Ratios & Dynamic Range

– Posted in: Cinematography & Lighting

Before you can create mood with lighting ratios, you need to understand the basics of dynamic range?

Dynamic range refers to a comparison between the brightest and the darkest areas in an image. In the low-key image above, most of the image falls within a very limited range at the bottom of this camera’s exposure limits. The measurements in the above photo are in f-stops, a camera setting allowing a measured amount of light to the sensor. This camera has somewhere around a 10 f-stop range.

  • About 60 % of the image is exposed between f-1 and f-2
  • About 5 % of the image is exposed between f-2.8 and f-5.6
  • Less than 5 % of the image is exposed beyond this camera’s upper exposure limit
  • About 30 % of the image is exposed below this camera’s bottom exposure limit

Don’t worry about being able to measure in f-stops. It’s enough if you know:

  • The window and a small portion of the window light on the floor exceed the dynamic range of this camera’s sensor, so there is no detail retained.
  • Most of the image is under-exposed and “low-key”
  • The mood is dark and mysterious
  • A trained cinematographer could design this plan on paper prior to arriving on-set

This image is from a horror project I recently shot, and I’ll be doing a lighting breakdown in a future blog post.

Possibly the most important thing a director needs to understand about dynamic range is that it is a limitation that must be respected.

Before a single light is set, the director needs to decide what the scene’s mood is.

You or your cinematographer need to understand the dynamic range limits of your camera as well as the amount of light coming in from existing windows and from your location’s practicals (e.g. the lamps and lights we see in the image). If you understand how your camera sees light, you’ll know what you need to do to set exposure and create a lighting design that fits the image in your mind’s eye.

My goal with this post is to:

  • Help you pre-visualize contrast ratios
  • Empower you with the common vocabulary used when discussing lighting
  • Keep you from creating impossible lighting scenarios

Here are three things you need to know to get the most value from this post:

  • The best cameras can process less than one tenth the dynamic range the human eye can.
  • If over 60 percent of an image is considered at mid-tone or less, the image is considered “low-key” and the mood is generally described as sad, tense, melancholy, etc.
  • If over 60 percent of an image is considered at mid-tone or above, the image is considered “high-key” and the mood is generally described as happy, uplifting, hopeful, etc.

A close-up of a person can easily take up most of the screen, so it’s important to consider the same lighting dynamics introduced above. These close-ups can be considered portraits, and the lighting is often referred to in terms of ratio. Ratio is the measured difference between the brightest side of the face and the shadow or darker (fill) side of the face.

The image of the woman to the left is beyond a 5:1 ratio. I know this because the best camera sensors can’t handle more than a 5:1 ratio before going to pure black on the bottom of the exposure range to pure white on the top.

The woman wearing the bow tie is lit using somewhere around a 4:1 lighting ratio. She’s likely lit with a large soft-box, so there is some light fall off on her right cheek, but not a lot. If you look at her cheek with the x and compare it to the shadow area of her forehead, this measures a 4:1 ratio. The ratio from one cheek to the other is 3:1.

All the numbers may seem a little confusing at first, but like all new things, you’ll develop the ability to quickly associate the numbers with the look. The horror project image above has a ratio of more than 5:1, but locations are rarely discussed in terms of ratio. They’re more likely to be referred to in terms of their contrast range.

For now, look at the two faces and note the difference in the degree of gradual fall off in the shadow areas. The close-up is lit with a harder light source. The shadow line is much more defined than it is with the woman wearing the bow-tie. The close-up portrait has no fill light. The lack of fill and being lit with a harder light results in the left side of her face “falling off” to full black. The bow-tie woman is lit with a large soft source and may have light or a bounce card filling the shadow side of her face. Notice the very gradual shadow line. It’s hardly a line at all. The “off-key” side of her face does not fall of into full black and retains detail.

The “key-side” is the side the strongest light source comes from. The “off-key” side is the opposite side of the key. 

You’ll also hear dynamic range referred to as contrast range. For the purposes of this post they’re the same thing.

The larger the difference (ratio) is between the bright and dark areas, the higher the contrast of the image is. The lower the ratio, the lower the contrast. The image of the woman on the bed with a laptop, breaks down like this.

  • Her face falls within a 2:1 ratio
  • Her forearm to the dark portion on the front of the dresser falls within a 3:1 ratio

Notice that while one area is very bright and the other is very dark, you can still make out detail and subtle shading differences in all but the brightest and darkest areas. These extremities represent a small portion of the image.  The areas that retain detail represent the light levels that fall within that camera’s dynamic range.

If I were describing how I wanted this shot to look before we started setting lights, I might say;

“I think overall the image should be slightly underexposed, not low-key, but more on the low side of mid-key. I’d like to brighten the shot slightly by having a warm lamp on the nightstand. I’d like to model her face as if it was lit by the laptop’s screen and complemented by the light in the background.  There should be no full black shadows.”

After listening to my desires, a good cinematographer would recognize:

  • The white pillow and the white comforter would be a large part of the scene and keeping these slightly under exposed would help determine the base layer of light needed
  • The exposure settings would likely be determined by manipulating the background lamp
  • The light on her face would need to be controlled and flagged off of the white comforter

These challenges would determine what kind of light, the amount of light and where the instruments were placed.

* Notice the comforter is built up behind the laptop. This is hiding a small LED light.

Here are the 3 most important questions a director can ask when assessing locations and production design.

  1. How large a ratio can my camera’s sensor handle before exposure drops below the bottom or above the top limits of its range? Each of these extremes results in lost image detail.
  2. If there are windows and existing lighting fixtures (practicals), do I (the director) want to incorporate them for story or style purposes?
  3. What is the mood and style statement I am trying to create with this image?

The contrast range and how your camera handles this range will determine how your image will look. Do you want shadow areas that are completely black or do you want the “darker” areas to be middle or even light gray? If there are windows, do you want to see out those windows?

The answers to these questions determine the look and mood of your image, as well as the lights and the plan needed.

If you liked this post, please checkout – 4 Lighting Tips for Directors

If you’re motivated to get more info now here’s a couple of videos that might help. Additional Videos – Understanding Lighting and Contrast Ratios

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