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Fill light

Shape your shadows - master the art of fill light in photography...

What is the fill light?

The fill light refers to additional light to reduce or eliminate shadows and create a more balanced exposure. It is typically used in combination with the main light source (key light) to illuminate the areas that would otherwise be in shadow.

Fill light helps to provide even lighting and "fill in" the subject's darker areas, resulting in a more pleasing and well-exposed image.

The fill light is a part of the three-point lighting setup along with the key light and backlight.

Three point lighting setup.
Three Point Lighting

First, we should address the elephant in the room. Every component in a three-point lighting setup is equally important. There will never be one without the other. Not knowing enough about each component is enough to serve as your next roadblock when learning photography and experimenting with lighting.

Although it is the secondary lighting, fill light itself determines the brightness, shadows, and overall contrast of the shot. These three factors that are affected by fill light will drastically determine how you use light to your advantage.

Where do you put a fill light?

As a secondary light, the sole fill light's purpose is to counteract the shadows that appear. To effectively do this, it is common for the lights to be placed on the opposite side of the key light.

For example:

If the key light is on the subject's left, the fill light would naturally be placed on the subject’s right.

What is the purpose of a fill light?

The purpose of the fill light is to fill in shadows. Because it’s placed on the opposite side of the key light, it perfectly exposes these little details hidden in the shadows.

Fill is often used to balance out the key light and make everything more natural. Using the “natural” light as a reference point, photographers increase or decrease the contrast.

How do you use fill light in photography?

There isn’t any particular right or wrong way to use fill lights. Different situations and themes will require different amounts. An image that only has key light with little backlight and no fill light will result in a rather dramatic image with lots of contrast because there is only one light.

For example, look at these images where I only used a key light and then an image where I added in a fill light as well. Notice how when I'm only using a key light, you'll see the contrast is strong because there is only light on one side of the mannequin's face:

Mannequin head being lit by key light.
Key light only
Mannequin head being lit by key light and fill light.
Key light and fill light

There are instances where photographers decide to use a lot of fill light, a medium amount of it, or none at all. As a rule of thumb, the more dramatic a scene gets, the less fill light is used. Comedy, romantic, or commercial scenes will often use the most amount of fill light to illuminate the scene, object, and subject's face to create a minimal amount of contrast for a bright and upbeat look.

Take TV Shows as an example. They always make sure to fully fill the shadows of the actor’s face, keeping the lighthearted comedy vibrancy alive. The more dramatic scenes where the peak of the MAX will use little to no fill light. The shadows and high contrast give a more mysterious and tense atmosphere around your shot.

There are many combinations for these scenes, such as the Rembrandt lighting, butterfly lighting, split lighting, loop lighting, Paramount, and many more. They just change the position and amount of key light, backlight, and lastly, fill light.

Different situations need different solutions!

How bright should fill light be?

Like above, the brightness of your fill lights should be adjusted to your needs and theme. You can either use no fill light or a minimum amount or use it as much as you used your key light. This brings us to the importance of the lighting ratio.

You might have also heard about the lighting ratio. Lighting ratio refers to comparing the intensity between your key light and fill.

It’s basically the contrast ratio between the bright and darker areas. This lighting ratio is connected to the angle of lighting and the amount of fill light. This is your biggest time saver for all-around consistent lighting.

Here are the common lighting ratios:

  • 1:1 ratio (even lighting) for a flat and even lighting across your subject
  • 2:1 ratio (low contrast) for a soft and subtle shadow with some depth and dimension
  • 3:1 ratio (moderate contrast) for a more pronouned shadow that is still natural looking (very flattering for portraits)
  • 4:1 ratio (higher contrast) for a dramatic and moody look where shadows are darker and more defined
  • 8:1 ratio (high contrast) for a very dramatic and intense look with stark contrast (usually for more artistic portraits)
Man in suit in front of white background.
3:1 lighting ratio

Your lighting ratio will be extremely important in documenting consistent lighting throughout a scene. It gives you easier access to previous light intensities that you used. Producing the same light intensity as the brightest and darkest areas of your subject.

Take note!

Understanding lighting ratios is more of a problem of consistency rather than amount.

Let me add a couple of notes, too, while we’re on this topic.

In general, your fill shouldn’t be brighter than your key light. Doing this will make your shot appear more natural. Use a diffuser, reflectors, or scrim, or create some distance between your subjects to achieve a softer fill. Oh right, do you know how to measure your fill light?

How to measure fill lights?

The first step in measuring your fill light or contrast ratio would be to buy a light meter.

Your key light is the main source of light, while the other is the fill light. The readings will be written in f-stops. So, how do you read f-stops? Be sure to check out our aperture and f-stop guide.

Well, if you had an f-stop of f/2.0 and increased it to f/2.8. By raising it, you’re effectively doubling the amount of incoming light. The reverse also applies, decreasing the f-stop from f/2.0 to f/1.4, which is equivalent to halving the amount of light.

Check out this visual to help further explain it:

Aperture f-stop chart.
Aperture f-stop chart

If your key light was an f/8.0 and your fill light was an f/4.0, then your contrast ratio would be 4:1. The key light has twice the amount of light, and it's two stops higher. Why two stops higher? Because the stops start from f/1.4, f/2.0, f/2.8, f/4.0, f/5.6, f/8.0 f/11, f/16, f/22, and lastly f/32. All stops in between are fractions of a whole stop.

So, if your key light was f/8.0 and the fill was f/5.6, the contrast would be 2:1! It’s just one stop and multiplies the amount of light by two. That’s how you easily measure fill lights.

What is the difference between key light and fill light?

Maybe start with the reason for their existence, i.e., their purpose. The purpose of the key light is to be the main source of light for a shot. On the other side, the fill light is a complementary source of light that fills in the shadows and decreases the contrast.


The key light will always be brighter than the fill light. It’s the key light; it sets everything up as the foundation, and it’s only natural for it to be brighter.

If you use a brighter fill light, your image will look unnaturally bright, and it will “technically” become a key light. The shadows would look weird, too, making the image look even more unnatural.

While key light will usually be the sun, light sky, or studio light, you can simply use a reflector as your fill light. Those are the main differences between the key and the fill light.

In conclusion, the fill light is simply a complimentary light with a big role. It’s responsible for creating depth and especially mood in an image. Normally, they’re placed on the opposite side of your key light to counteract the unflattering shadows. To use it effectively, you need the other components (key lights and backlights) and the much-needed knowledge to use them.

The more you experience the difference by changing the brightness around and experimenting with it, the better you’ll get at using them. Have fun!

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