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

How to use key lighting in photography with natural light

Sometimes only a key light is used, sometimes additional lighting is used, such as fill light to lighten the shadows. In the above natural light image the only light used was the indirect light of the sun. 

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

How to set the key light in photography

Lit by natural light and flash. I metered for the ambient light and kept my camera settings the same for all three photos, adjusting just the flash output (my key light) until I reached the look I wanted.

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

Natural light vs flash for key lighting

For the left photo I used natural light only with a shutter speed of 1/500. For the photo on the right I lit her with flash, increased the shutter speed to 1/1000 and used the setting sun behind her as a backlight. As a result the shadows in the natural light photo are softer and there’s less contrast.

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.

Controlling light ratio of key light and fill light

I used flash and natural light for both photos. I adjusted my flash and exposure settings between the two photos so that the photo on the left is mid key and the photo on the right is low key.

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:

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

How to use flash as key lighting and backlight

Both photos use a combination of flash and natural light. The flash position did not change. On the left she’s lit with natural light and I used flash as a backlight. On the right she’s lit from the front with flash as the key light and natural light as a fill light.

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.

Low key lighting with and without the key light

The silhouette photo is with natural light only and in the photo on the right I lit her with flash to camera right as a key light. Camera setting for both photos are 1/1600, f3.2, ISO 200.

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

Low key lighting and high key lighting with natural light

I took these two photos 6 minutes apart with natural light only as the setting sun disappeared behind a building. The photo on the left, is low key with deep shadows and the photo on the right, is high key.

I adjusted my shutter speed between photos for the changing lighting conditions – 1/800 on the left to expose for the direct light on his face (making the background darker) and 1/200 on the right to cope with less light (making the balance of light between background and subject similar). 

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

Leave a comment

If you have any questions about key light photography, let us know in the comments.

Also, I love good news, so if my portrait lighting tips have helped you to understand what is a key light in photography, share that too.

2 thoughts on “What is a key light in photography and how do you use it?”

  1. Hi Jane,
    Very well written and detailed explanation on Key Light and how to use it.
    * You will need to swap the shutter speeds in the last paragraph describing the lighting used on the man. I read every word and can fill in where a word is missed or left out but this minor mistake could confuse a reader.
    Love your stuff!

    Brian

    Reply
    • Hi Brian
      Thank you so much for pointing that out – really appreciate it! I’ve fixed it now. You wouldn’t believe how often I catch myself making that mistake when writing these articles.

      Reply

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