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Key light vs fill light: What’s different and how to use?

In video making, a key light is always the start and then a fill light may be added to keep the scene dramatic, and probably more lights would be decisions to light the image to be an photograph. Here we would like to discuss the two main lights in photography - key light vs fill light - and try to make it clear about their uses.

What is key light?

A key light is usually the main light source with highest intensity among all the lights that are used on a set. When in the image, it is used to help shape the subject since it is designed to target the subject wherever the subject’s position is. In order to achieve the satisfying results photographers desire, a LED key light can be placed on the front or side and at the angle straight on the subject or above or below.

The key light always plays the main role in photography. Generally speaking, it is placed first so that the rest of the lighting can be set accordingly to offer support and filling. When it comes to placement, photographers should consider the effects they are going for. Here are some ways of placements to try.

  • At various heights and angles

There is a common method called “Side Lighting”, which is to place the main light to one side of the subject, falling on only half of their face, for characterizing conflict emotions. Placing this video light at a higher elevation can deepen the shadows of subject’s eye socket for an unwelcome personality shaping, while placing at a lower elevation, like below the subject, gives a horrifying look since it falls on the chins and nose from below.

  • Behind the subject

Once the key light for photography put behind the subject, the subject would be in complete shadow. It is called Silhouette, a way to create a dramatic and mysterious atmosphere, also keeping the subject out of the focus.

  • In front of the subject

Flat Video Lighting means placing the light on top of the camera to fall directly on the subject, seemingly able to erase tiny facial shadows and widen the face. It sometimes is called Glamour Lighting since it can improve the look of models. However, it is not the right way to use if photographers are seeking for characteristic look.

What is fill light?

To define fill light, first thing to know is that sometimes when in a photo shooting set, other lights (mostly key light) is bound to result in shadows. Hence comes this type of photography light to fill up those shadow. A fill light is usually diffused enough not to cause its own harsh shadow. Considering the budget, size of space and the key light modifier, there are quite a lot choices.

The fill light is the second. It is different from the key light since setting a fill light should not create another shadow. That is, when there is a second shadow, it means the fixture is too strong and requires adjustments, such as dimming or re-placing the light. Another way is by means of diffusion materials - like neutral density gels, or scrims - reduces the light but not softening it.

Please take notice that, a fill light does not always have to be a separate light. A simple and low-budget way is light reflection from the key light which is set to reflect lights on the subject. The inexpensive and stiff white foam core boards and portable reflectors are often being used in this case. Other reflective materials also works well as long as they do not give colors into shadow and reflect the light properly.

Additionally, negative fill light is its alternative option, which can play the opposite role in photography. If you want to know something more, please click the word..


Each photography fill light serves its own purpose for different lighting effect. It is important to choose the proper kind so as to achieve the ideal results. There are two main types:

  • LED fill light, as the most common one, is available for light intensity and angle adjustment, better meeting the needs for photography.
  • Reflector, as another common type, produces reflected light depending on the distance from the subject and materials of production.

If you what to know more info, please see Basics for newcomers to fill light

How to use them in portrait photography?

As the key light is set to illuminate the subject while the fill light is set to reduce the shadows, let’s talk about how to use both of these lights in an effective way for portrait photography. This setup not only works for human portraits but is also a good setup of lighting for pet photography.

Use of key light and fill light

1. Try out key and fill light positions

When in a photography set, carefully try out the position for key light and fill light in turns with each of it’s light on. To begin with, try placing them separately in 8 o’clock and 5 o’clock position.

2. Try out the effect for the main light

Take a test shot with the key light on and the fill light off, then see how it shapes the subject’s face in a three-dimensional degree. Notice if the shadows on the face now is too deep and creates too much contrasts.

3. Try out the effect for the second light

Next, take another test shot with the fill light on and key light off and make sure to lock the exposure so as to find out the underexposed portrait. Simply look at the shadows from the nose. It is not hard to find out that compared with the key light, the fill light stays more straight on the subject, making the lighting flatter.

4. Combine the key and fill light together

Now take another test shot with both key and fill light on and the exposure metered. This time, look how the fill light balance the lighting by filling up the deep shadows. Also, the contrast stays subtle since the relation between these lights is even. If more contrast required, try to turn down the fill light little by little.

What could be additions for YouTube video lighting?

A standard lighting technique - Three Point Lighting - is often used to light YouTube. In this way, video makers can turn a rather flat and ordinary image into a dynamic and interesting image, leading to a video that pops. In addition to the said key light and fill light, the third role is backlight.

It can help distinguish the subject from the background. You may find it helpful to have barn door on this light in case of being accidental captured in the camera lens. When using this type of YouTube light, attach a dimmer would give the proper highlight in accordance with the color tone of subject. Apart from using a dimmer, adding a scrim or a diffusion paper would be better for softening the back light while reducing the intensity.