What is a key light in photography and how do you use it?

Lighting is the defining element of any photo. It sets the mood, making it either uplifting and cheerful, or mysterious and moody and everything in between. The key light in photography defines a photo’s mood, so it’s the most important light around which all other lighting decisions are made.

Before we figure out how to use key lighting, we should first understand exactly what it is.

What is a key light in photography?

I’ll start with what it’s not. A key light is not any specific type of light. Any light source can be used as a key light in photography.

The key light in any scene is the primary source of light used to light the subject, so key light examples are:

• A natural light shooter uses the sun as the main light source
• A flash photographer could use either flash or the sun as their main light source. I’ll explain more in a moment
• When photographing at night using neon signs to light subjects, like Brandon Woelfel, the sign is your primary light source

Sometimes only a key light is used, sometimes additional lighting is used, either as fill light to lighten the shadows or as the main light. 

However many lights you use, there’ll always be a key light.

How do you use a key light in photography?

When we add light to anything, we create form.

This is most obvious when we think of silhouettes, which are simply shapes with no depth or dimension, because they’re lit from behind. There’s no light skimming across the surface of the subject to create form by illuminating peaks and casting shadows, adding depth to dips with shadow.

This is the key light at work – creating a three dimensional look to an object on a two dimensional piece of paper or screen.

Key lighting can be used in three ways to set the mood and create different aesthetics:

• High key lighting – minimal tonal contrast, light and airy
• Mid key lighting – some shadow, looks normal
• Low key lighting – deep shadow, very contrasty, dark and moody

Although the main light is the most important light, it’s the balance between this and how bright the background is that determines whether an image is:

• High key (bright background)
• Mid key (background is the same as the subject)
• Low key (dark background)

So, it all comes down to balancing the ratio of other light in relation to the key light in photography.

Where is the key light placed?

Because key lighting lights your subject, key light placement is very important as it:

• Influences the mood of the photo
• Is used to flatter the subject

With natural light photography, where you place your subject in relation to the light is important, but the same rules apply in terms of portrait lighting patterns.

When using flash to light the subject, you have more freedom as you can place your lighting in relation to the subject. You can also adjust it for more flattering results.

Examples of portrait lighting patterns for artificial light and natural light are:

• Butterfly lighting
• Loop lighting
• Rembrandt lighting
• Split lighting

Two ways to modify portrait lighting patterns, depending on where you place the key light:

• Broad lighting
• Short lighting

How do you set up key lights?

I mentioned earlier when using flash as the main light source, you can use the sun as a fill light and vice versa. It’s your choice, based on the key light position in relation to the subject and how bright it is.

If you use flash to illuminate the subject, it’s the key light and the ambient light can be the fill or backlight.

When natural light illuminates the subject, it’s the key light and flash can be used as fill or backlight.

Even a reflector can be used as key light if it’s used as the main light to light the subject. This is most often the case when photographing in the golden hour with the sun behind the subject and a reflector in front bouncing light back into the subject.

Regardless of what key lighting you use to light your subject, the main light is the light that you meter to correctly expose your subject.

Steps to setting flash as the key light outdoors:

• Place your subject in open shade or with their back to the sun if you want to use the sun as backlight
• Meter the ambient light
• Position your flash to light your subject with the portrait lighting pattern you prefer
• Meter and set the flash to ensure that your subject is correctly exposed in relation to the ambient and backlight and how dark or bright you want the background to be

Further reading: Getting started with off camera flash

Steps to setting natural light as the key light outdoors:

• Position your subject in open shade or in direct sunlight so that the light falling on them creates the portrait lighting pattern you prefer
• Meter the light on your subject and set your camera’s exposure settings
• In portrait photography, when using your camera’s reflective meter, use spot metering to meter the exposure off the subject’s cheek, just below the eye
• Alternatively, use a light meter to measure light falling on your subject (point it at the light)
• Decide on how deep you want the shadows to be and if you need to use a reflector as a fill light to lift the shadows

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