What is Fill Light? Photography Definition, Tips, and Examples

This is a guide covering fill light.

In this glossary definition you’ll learn about:

If you ever used a three-point lighting setup, you’ll recognize the importance of fill light. At first, it looks like a small piece and gets easily overlooked.

Let’s dive in.

fill light

What is Fill Light?

Fill light illuminates the darkness and reduces shadows with its light.

First of all, we should address the elephant in the room. Every component in a three-point lighting setup holds the same degree of importance.

There will never be one without the other. Not knowing enough about each component is just enough to serve as your next roadblock when studying and experimenting with lighting.

Although it is the secondary lighting fill light itself that determines your brightness, shadows, and overall contrast of the shot.

These three factors that are affected by fill light will drastically determine how you light to your advantage.

The more knowledge you have of lighting and experience in manipulating it, the more likely you are to understand that fill light will either make or break your shot.

It determines your lighting style, therefore affecting the corresponding feel of the photo.

purpose of key light

What is the Purpose of a Fill Light?

Based on the fill light meaning, it is clear that the fill light’s purpose is to fill in the shadows. By filling the shadows it affects a scenes visual style, depth, contrast, and also shadows.

Photographers will also commonly use it to expose subjects/objects to interesting details. It perfectly exposes these little details hidden in the shadows because it’s placed at the opposite side from the key lights.

A myriad of effects can be acquired by using different ratios from Key light to fill light. Commonly, photographers will use 2:1 ratios to achieve the simple yet flattering look. Some even go to ratios of 8:1 to make the shot look even more dramatic.

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

fill light purpose
Photo by NeONBRAND

Where do You Put a Fill Light?

As a secondary light, the sole fill light 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 to the key light.

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

The more similar angle of the key light that you can locate your fill light opposite at, the better

. You can also experiment with your fill light, by starting to expose your shot with the only key light. Now, look at your shot and see the unwanted shadows appear, contrasts that are too great, and the “changing of your models face.”

If you see some shadows that you don’t like, pop out your fill light and fill the area to expose it. But this leads to the next problem, how do you effectively use it?

studio lighting

How Do You Use Fill Light in Photography?

There isn’t any particular right or wrong way when it comes to the usage of fill light. Different situations and themes will require a different amount of fill lights.

An image that only has key light with little backlight and no fill light will result in a rather flat image. It’s not really flattering when taking images with this setup, it looks amateurish but still fine to a certain extent.

There are instances where photographers decide to use a lot of fill light, a medium amount of it, and 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 subjects face. There is a minimal amount of contrast and shadows here.

You can take TV Shows as an example, they always make sure to fully fill the shadows of the actor’s face. It keeps 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 gives a more mysterious and tense atmosphere around your shot.

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

rembrandt lighting
Photo by Joy

Most of the names are derived from the person who popularized the usage of the said lighting (Rembrandt in his paintings and Paramount in their movies).

Each type of lighting is used in different situations and models.

Let’s use the Rembrandt lighting as an example. You can easily identify it by the dynamic shapes (triangles) that are formed on the subject’s cheek. The shadow that it forms creates an air of mysteriousness around it, while also making a shadow that aligns with the subject’s jaw which presumably makes them slimmer.

Each piece of lighting has its own unique appeal and special shadows that make it more identifiable.

See it as just like making a cup of coffee, you constantly adjust your drink to fit your mood and needs. Want it more three dimensional, then use less creamer and less sugar. Feeling moody and dramatic? Then use a lot of coffee and cream.

Different situations need different solutions!

How Bright Should Fill Light Be?

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

You might have also heard about contrast ratio. Contrast ratio refers to the comparison of the intensity between your key light and fill.

It’s basically the contrast ratio between the bright and darker areas. This contrast 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.

The flat 1:1 lighting has the same use as the 2:1 ratio. Good for scenes where you want to give a feeling of openness and lightheartedness, such as comedy shows, interviews, or commercials. The high contrast ratio 4:1 and alike, creates more shadows, which translates into more drama and tension.

Your contrast ratio will be extremely important in documenting consistent lighting throughout a scene.

It gives you easier access to previous light intensities that you used before. Producing the same light intensity that the brightest and darkest area of your subject.

It’s more of a problem of consistency, rather than amount. There is no best brightness, there is just the generally used 2:1 ratio.

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 create some distance between your subjects to achieve a softer fill. Oh right, do you know how to measure your fill light?

rembrandt fill light
Photo by Marshal Quast

How to Measure Fill Lights?

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

Simply measure your main source of light and the area lit by a weaker light source afterwards. The main source of light is your key light, while the other is the fill light. The readings will be written in f-stops.

So how to read f-stops? Well, if you had an f-stop of f/2.0 and you 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 is equivalent to halving the amount of light.

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 its 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-betweens 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 multiples 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 key light purpose is to essentially be the main source of light for a shot.

On the other side, the fill light meaning is a complementary source of light that fills in the shadows and decreases the contrast.

Key light will always be brighter than 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, then your image will look unnaturally bright and it would “technically” become a key light. The shadows would look weird too, making the image look even more unnatural.

Secondly, if you will always use key light because it’s your main source of light. Fill light may be unessential in certain conditions when creating dramatic photos.

While key light will usually be the sun, light sky, studio light you can simply use a reflector as your fill light.

Those are the main differences to distinguish between the key and fill light.

studio light meter
Photo by Emmanuel Acua

Final Remarks

The fill light definition 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) with the much-needed knowledge to use them.

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

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