Film & TV

What Is a Fill Light? Learn About 7 Types of Fill Lights and the Best Ways to Use a Fill Light to Achieve Mood

Written by MasterClass

Jun 10, 2019 • 5 min read

In film production, cinematographers carefully consider their lighting setup and the role it plays in creating a certain mood. Using a key light in a three-point lighting setup results in dramatic, dark, and deep shadows, which sets a mood that is suited to a noir or horror production. If a cinematographer wants a lighter, airier mood—or even just shadows with more visible detail—they balance out the key light with a fill light.

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What Is a Fill Light?

In traditional three-point lighting, the fill light is a less powerful light that sits opposite the primary key light. From this different angle, it will literally fill in the high-contrast shadows that the key light creates on a subject’s face. The fill brings out details in the darkness to affect whatever mood the cinematographer (a.k.a. Director of Photography, or DP) desires.

7 Types of Fill Lights

Depending upon your financial constraints and needs in a scene, there are several types of lighting techniques you can use to achieve your desired fill light effect.

  1. Lighting units. An actual light is your most obvious source of fill light. However, a lighting rig may be out of your budget. If you only can afford one light, you should always prioritize the key light.
  2. Reflectors. These modifiers, which are inexpensive, portable, and available in a variety of sizes and colors, simply reflect the key light back towards the subject. The color of the reflector will modify the shadow. A gold reflector will cause warmer tones on the subject. Many reflectors do not take up much space and do not require the set-up of a light stand. A white foam board that bounces light can be ideal for outdoor shoots, as foam boards are durable and do not shake in the wind. Any reflective material can act as a fill light as long as it does not introduce a new color into the shadow. However, reflective surfaces such as mirrors and aluminum often reflect too much light back onto the subject.
  3. Walls. Walls and ceilings can also act as large reflectors of light, bouncing back the key light. This helps create a soft and subtle lighting effect.
  4. Fabric. Clothing is another option when it comes to picking a reflector. Lighter-colored clothes can also create a subtle effect, so you may opt to have your crew wear some.
  5. Flash. Another way to provide fill light is a flash. In a well-lit situation, a flash will remove shadows and can go a long way. Another advantage of using a fill flash is that you can shoot the subject with the sun behind their back. This is similar to a strobe light. While more expensive and higher maintenance in terms of set up, a strobe can be a useful tool. Because it does not require a key light to reflect off of it, it can be placed anywhere on set for the desired effect. You can alter the amount of light the strobe emits as well as the level of diffusion.
  6. Negative fill. When a cinematographer wants a fill light that is darker than what is natural light provides, they simply block the ambient light with a black or opaque flag mounted on a butterfly frame. This prevents excess light from bouncing back at the subject. The amount of negative fill that you use is contingent on how much light you want to absorb. Light sources, situation, and the type of camera you are using can affect this.
  7. Spill fill. In production, stray light, including light leaks, may negatively affect a shot. The best way to avoid this spill is to work in a dedicated studio space where you have greater control over light sources and spill becomes a more predictable variable.

How to Measure Fill Lights

Cinematographers measure fill lights using a “fill light ratio,” also known as a “key/fill ratio.”

  • The fill light ratio describes the relative amount of light from the primary key light and the secondary fill light that fills in shadows the key creates.
  • A lower, more balanced fill ratio, like 2:1, creates a soft, flattering look that also tends to hide blemishes in the skin when your subjects are people. This soft light is “high key lighting” and creates an optimistic, upbeat, youthful, light, and airy mood that is common in sitcoms and comedies.
  • In higher fill ratio, like 8:1, where the key is eight times stronger than the fill, the key casts sharp-edged shadows that contrast sharply with the light. This is “low key lighting,” which creates a dramatic, mysterious, unsettling, and alienating mood and can display a range of deep negative emotions. As such, it is common in dark dramas, thrillers, horror, and film noir.

6 Ways to Use Fill Lighting

Hollywood cinematographers utilize fill lights in a variety of ways to achieve different looks and moods. As is best practice in all disciplines, before you break the rules, you should master the basics.

  1. Light placement is incredibly impactful on the image you create. A fill light works best when you position it at a general opposite angle from the key, your main light. If you place the key slightly off to the side of the camera and the front of the subject, on a light stand at a 45-degree angle to the camera, creating high-contrast shadows on the side of the face, the fill should be on the left at a similar angle. (In contrast, the backlight or rim light, which highlights the subject’s outline, separating them from the background and creating depth, should hit an actor or object from behind and slightly above them.)
  2. Typically, the fill light is less bright than the key, the primary source of light. In fact, it is customary that the fill is half as bright. You can control the fill light’s brightness by using diffusers and modifiers and adjusting its distance from the subject. (The further the light is from an actor, the softer its effect will be on them.)
  3. Some commons diffusers you can use to soften hard light include silks, scrims (small metal objects that DPs place inside a light to slightly reduce the intensity of the light without altering any other elements of that light source), and neutral density gels. All of these techniques can reduce light without changing its color.
  4. It can also be a good idea to experiment with your bulbs that create a varied effect.
  5. It’s important that the fill light remains indistinctive and does not create any shadows of its own. If the fill light is creating a second shadow, you should dim the brightness of the source. The fill light will create fewer shadows when it is closer to the camera.
  6. Where you place your lights relative to your subject and the camera determines where shadows fall. This relates to sensibly creating an environment—if your key light represents the sun, it should accurately reflect the angle and height of that source. How you position your fill and backlight affects whether there are deep, moody shadows or an optimistic, even light cast across your scene.

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