What Is Fill Light and How Can It Improve Your Lighting Setup?

Every scene has a main or key light, but more often than not, your key light will benefit from the addition of a fill light, too. Fill lighting is there to lift the shadows created by the key light, bring out the details in and add dynamism to a shot.

Think of the fill light as your key light’s right-hand person; they work as a duo, a little like Sherlock Holmes and Dr. Watson or Xena and Gabrielle. Knowing how to manipulate your fill light can make an enormous difference to the look and feel of your films. With a fill light, you can control contrast, brightness, the depth of shadows, and a scene’s dimension. It’s not so much key light vs. fill light, but key light and fill light.

What is a fill light?

When working with a 3-point lighting setup, your key light is your main light, usually positioned somewhere between 30 and 45º camera-left or camera-right. Your fill light will act as a balance to the key light, sitting at roughly the same angle but on the opposite side of the camera. The 3rd light in the 3-point lighting setup is the backlight (sometimes known as a hair light or rim light), which helps separate the subject from the background and provide depth to the scene.

The fill light won’t be as bright as your key light, but exactly how bright you want it will depend on the type of lighting that you want for your scene. It also doesn’t have to be a light. We’ll come back to both of these points later.

Fill lights aren’t restricted to 3-point lighting setups, though. If you are shooting in natural light, you might find that you need to lift the shadows, especially if you are using the sun for backlighting and don’t want to create a silhouette. If you’re using overhead lighting, a fill light coming from beneath can counteract dark shadows beneath your subject’s eyes, nose, and chin.

Anywhere you need to light the shadows created by your key light, you use a fill light.

What does a fill light do?

There are 4 main areas where a fill light benefits your scene:

1. Determining the contrast ratio in your shot – or the difference between the lightest and the darkest areas of your shot

The fill light from this shot, coming from underneath, is a great illustration.

2. Creating depth and dimension

Key light from camera-right, fill light from camera-left, and it evens up the lighting.

3. Producing a more even lighting style

Without a corresponding fill light, this scene would not look as bright, airy and positive.

4. Bringing out the details and shapes of a subject

Fill light ensures there’s plenty of detail in the scene.

How to use a fill light in different lighting set-ups

Whether creating a YouTube lighting setup or something for a commercial or documentary, your fill light is secondary to your key light. Therefore, it should be counteracting the shadows cast by your key light and not creating any of its own. To ensure this, there are three factors that you need to consider when deploying your fill light.

• First is its position. It should be balancing the key light.
• Next is its quality. So that it doesn’t create any shadows of its own, a fill light usually creates soft light that is diffuse. You can use a diffuser to help achieve this if the shadows are too definite and compete with those from the key light.
• Finally, you should consider the intensity of the light from your fill light. The relationship between the quantity of light from the key light and the fill light is referred to as the fill light ratio or the key/fill ratio. The key light will always be stronger than the fill light, but you will produce a brighter, more softly lit shot by using more fill light. Use less fill light, and your shot will have more contrast and more defined shadows.

A ratio of 2:1, with the key light being twice as intense as the fill light, is a good place to start. This produces a softer lighting look without too many shadows and not much contrast.

For a high key lighting effect, which will look optimistic, upbeat and airy, you will want a lower fill ratio, but start at 2:1 and see how it looks. Again, the fill light shouldn’t be brighter than the key light.

If you want a darker, moodier low key look, you can reduce the intensity of the fill light considerably, with a ratio of maybe 8:1. Whatever the look and feel of your film, it will be dependent on the ratio of your fill light to your key light.

Types of fill lights

Lighting units

Another light, less intense than your key light, is probably the first light you might think of as a fill light in video (or in photography). For example, if you use a softbox or umbrella as your key light, you can use a 2nd one, set to a lower intensity, as your fill light. And while you might think of a ring light as a key light, it can be used to great effect as a fill light. If you’re trying to create a more natural feel from your fill light, try using a practical, which could be anything from a desk lamp to a tablet or mobile phone.

Reflectors and bounce cards

As mentioned earlier, your fill light doesn’t have to come from a lighting unit. Reflectors and bounce boards make excellent fill lights. If you’re filming using natural light and can’t rig up a lighting unit, a reflector can be just the thing to fill the shadows in a sunlit scene. They’re not restricted to location shoots, though. They can do the job in a studio or set, especially if you don’t need a very strong light source. A reflector can bring out the detail in a scene without losing too much contrast.

Walls

White or pale-colored walls will bounce light back onto your scene from your key light in a soft, diffuse way. It’s a great way of making use of all of your set, but be sure that your subjects know precisely where they need to be so that light falls accurately on them to lift the shadows the way you want it.

Negative fill

Negative fill lighting, or neg fill, is the opposite of a reflector. It’s a black flag or piece of fabric that you use to block off light from reaching your scene to ensure that you retain a higher degree of contrast in your scene.

Wrapping things up

Your fill light is one of the most valuable tools in your filmmaking kit. It can change the look and feel of your work with just a few adjustments, and it doesn’t even have to be a lighting unit. So grab a reflector and see just what definition a fill light can bring to your films.