What is fill light in photography – and how to use it

Once new photographers wrap their heads around how light direction impacts an image, the next logical step is controlling light. And that’s where fill lighting comes in. Fill light in photography isn’t just for flash photography. Far from it! Natural light photographers use fill light just as much as strobe photographers. It’s just different lighting techniques.

Fill light photography can be as complicated or as simple as you like. In fact, you probably already know about it, even if you think you don’t. Fill light controls the shadow areas of an image, brightening dark shadows created by the main light source.

What is a key light – key light vs fill light?

Before we can get into the details of fill, we must first look at what is a key light, which is actually quite simple. A key light is just another way of saying main light. 

So, for natural light photographers the main light is the sun. For flash photographers the key light could be the sun or their flash (either on or off camera), depending on how they use it. It could also be continuous light (such as a ring light or LED light).

Every photo needs a key light, but not every photo needs a fill light. But don’t let that fool you into thinking fill light isn’t that important – here’s why… 

What is fill lighting in photography?

Fill light is any type of light that is less bright than the key light and is used to fill in the shadow details caused by the key light. Using a main light as well as a fill light is called a two light set up. Fill lighting doesn’t even have to be an actual light, but we’ll get to that in a moment.

Fill light controls the depth of shadows in an image and therefore impacts whether an image is high contrast or low contrast, depending on how much fill is used.

In the studio you have complete control over light, so you set your main light at whatever brightness you want and then the fill light less bright. This is the essence of using lighting ratio to control shadows and I strongly advise using a light meter for this. How bright or dim the fill flash is depends on the image you want to create and the light ratio you use by adjusting the power settings of your strobes. 

When using off camera flash for outdoor portraits you can use the sun as either the main light source or for fill, and flash as fill or as your main, depending on:

• Time of day
• the power of your flash lighting
• and the amount of light required to fill in the shadows

In natural light photography, the main light is always the sun, but that’s not the only light available to natural light photographers. A fill light source can be reflected light or even ambient light (such as a room light indoors).

 

What is reflected fill light?

The clue’s in the name. Reflected light is any light that’s reflected back onto the subject.

You can create reflected light with:

• A light reflector – either one you bought or something you made (anything that reflects light back onto the subject is a reflector)
• A white wall
• The ground, such as beach sand (like in the image above), gravel, even grass
• Any shiny surface, including water
• Light colored clothing

However, be careful about the color of the object that’s reflecting light. If it’s green, for example, the light bouncing off it will be green, which then casts a green light over your subject. This is why when you photograph on grass in midday sun your subjects look a bit green.

For these photos I hung my reflector from a tree slightly to camera left. In the image above I used the white side of the reflector, which has a matte finish.

However, in the image below I used the gold side, which is much brighter and more reflective than the white reflector. The color temperature is too yellow, the light is too harsh for the photo and the shadows on the subject’s face are all wrong – her neck is brighter than her forehead.

What is fill light used for?

Sometimes it’s as simple as it sounds – fill light is for filling in the shadows:

• If you don’t want deep shadow in your image
• To soften hard shadows and increase shadow detail
• When your subject is lit from behind (backlit)

Fill light, despite playing second fiddle to the key light, is actually just as important for creating atmosphere in photos. How much light you use as fill can completely change the mood of a photo by changing the shadows. Consider:

• Dark and moody – with lots of deep shadows
• Light and airy – with very little shadow

What kind of light is good for fill light?

Any secondary light source can be used for fill light. What matters is that the light is diffused. Fill needs to be soft light, because its job is to fill in shadows. If it were a hard light, it could create shadows instead of lifting them.

Natural light is diffused when it’s:

• Not shining directly on the subject, for example when the subject’s in the shade
• Reflected off a non-shiny surface, such as a white wall
• Partially blocked by thin material, such as net curtains

Flash can be diffused by:

• Using light modifiers such as softboxes or photography umbrellas
• Bouncing the flash light off a non-shiny surface, such as a wall, onto the subject

What’s the difference between hard light and soft light?

The difference between hard light and soft light is referred to as light quality. Think of your shadow on a very bright sunny day versus your shadow on an overcast day.

• On a sunny day the light is hard, so the transition between light and shadow is sudden. This is a hard light quality.
• On an overcast day your shadow isn’t clearly defined and the transition from light to shadow is much more gradual. This is a soft light quality.

I didn’t use a reflector, even though she’s backlit, so there’s shadow on her face. As it was an overcast day the light was very diffused so the shadows were soft.

Where should you place a fill light?

To decide on where to place fill, we must consider direction of light, because it’s not just about the direction of the main light. Fill lighting direction is also very important.

Fill lighting placed behind camera

In portrait photography using studio strobes, the fill light position is very often behind the camera to flood an even flow of light into the scene’s shadows from the front of the subject. It’s especially essential when the subject is backlit.

In the above photo I didn’t use any fill, but in the image below I placed fill lighting behind me. I wanted shadows, but not as deep as in the image above with no fill.

Fill lighting from the side of the camera

When placing fill lighting to the side of a camera, it should ideally be on the same side of the subject as the main light for a more natural look. In other words, place fill lighting on axis with the lens when using side lighting.

This avoids conflicting shadows falling on the subject’s face.

Fill lighting from below the camera

We’re used to light coming from above, so your main light should never be positioned below your subject shining up, but your fill can.

In fact fill lighting is very often placed below the subject in portrait photography so that the light fills in the shadows beneath the chin. Clamshell lighting is exactly this – the main light is placed in front of and above the subject with the fill light in front of and below the subject. It’s a classic portrait lighting technique for beauty photography.

When the fill light is below the subject make sure that its intensity is less than the main light. In other words it’s not as bright as the main light.

This lighting cheat sheet will help you think through lighting direction.

 

Using fill with flat lighting

The two times that fill light is as bright as the main light is when you:

• Create a high key image
• Want flat lighting

The aim in both instances is to have as little shadow as possible on the subject.

I used a high key lighting set up in the studio with the fill light set equal to the key light

The first portrait photographer that springs to mind when I think of flat lighting is Sue Bryce. She’s predominantly a natural light photographer who perfected the art of flat lighting her subjects using diffused light as a main light and reflected light for fill.

What is negative fill?

Just when you thought we were done with fill lighting, here’s a twist – negative fill. Instead of adding in light it’s another way to control light by absorbing it.

With negative fill you place something black near your subject to absorb the light for dramatic effect and therefore increase the depth of the shadows. The black material is referred to as a flag (aka black flags) in photography.

It could be any non-reflective black material, such as black cardboard. Even the black shirt you’re wearing if photographing close to your subject can be used as negative fill to deepen the shadows of the key light.

What you wear affects fill light

Photographers don’t wear black just as a fashion statement. Black absorbs light, so wearing black prevents light bouncing off your clothing back into the subject. 

That said, when photographing newborns using natural light I’ve often worn white to maximise available light by reflecting light to lighten shadows. So my clothing becomes the reflector.

Wrapping up fill lighting

Every photo needs a key light, but not every photo needs a fill light. However, when it is used, it has a huge impact on a photo – both good and bad.

The more you develop your photography skills, especially lighting techniques, the more you’ll find yourself focusing on fill lighting and all the creativity that two light setups give. 

You don’t need to know everything about photography lighting all at once. You can build up your knowledge in blocks, starting with a single light source, until you have a thorough understanding of the fundamentals of light.

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