The light in a photo falls into one of two different categories, fill or key. Now, I'm not just talking about the light from a flash but any kind of light. Fill light is light that serves to fill in shadows to create a more even exposure for example. Look at the light on this girl's face. It's completely even and soft. There are no dark shadows under her eyes, or under her chin. This was shot in a narrow street where the light was bouncing around so much that it just created this really nice fill light that wrapped around everything in the scene and created that even fill that eliminates shadows.

Yes, there are shadows in the corner of the frame, but those are the result of the vignette that I added in post-production. A fill light does not define the subject of the image. It is simply there to help brighten darker shadows on the subject, and throughout the scene. A key light is a light that serves specifically to illuminate your subject. Here, a bright shaft of light in an alley is shining directly on my subject. Here's another example, the clouds broke in a way that hit this statue and lit it all up really dramatically. In both of these instances a light source is directly lighting the thing that I'm taking a picture of.

Yes, I'm composing around that subject, and so have concerns about the lighting in the background. I want to be sure the background is visible, but there is a key light source that is serving to illuminate the subject in my scene. Here's another example. The tree is being lit by a key light source. And as with all of these images that we've been looking at, that key light source is, of course, the sun. In all these images, the sun has also created a lot of fill light as it bounces around the scene. So, really, we've got a single light source in these images that is serving both as a key, and a fill light.

The important thing to realize here is that regardless of where its coming from, the light that is serving to fully illuminate and reveal my subject is considered a key light, while the light that is brightening the rest of the scene is considered fill light. Sometimes it's actually a key light itself that catches your eye. I saw this spill of light on a wall. And so liked the geometry that it created. That I built a shot around it. Needless to say, this light is a key light. In all of these instances, the key light and the fill light that we're talking about is found light.

It's natural light. Light created in all of these pictures by the sun. There will be other times when you will work with available light that's coming from artificial light sources. But in those situations, you'll still be exploiting the lights either as fill or key sources. Now right now, this set is being lit by a bunch of different lights. They are working together to create both key and fill. Watch what happens when we turn off the light that is serving to create fill on me. So I am still lit by the key light but there are all these shadows on my face now.

Yes you can still see the background but that's being lit by other fill lights. Let's bring the fill light back up. And now let's turn off the key light. Okay, there is still light on me but it's only fill light. You can see me but I'm not necessarily the subject of the image. Okay, I'm, I'm the only thing on a bare white stage, but you know what I mean. Without the key light, your eye has a harder time finding it's way through a scene. So from all this, you can probably guess where I am going. When you shoot with flash, your flash will either serve as a fill light or a key light.

In certain situations, your flash might do double duty as both a fill and a key, just like the sun often does, but to learn to use flash effectively you need to start thinking about what type of light your scene needs. Does it need fill? Or does it need key? There are no fill or key buttons on your flash. The role your flash serves will be determined by where you position the flash, the intensity of the flash, and the exposure settings on your camera. Now, obviously we're going to go into great detail on all of these subjects. But the real work of being a good flash shooter begins with you conceptualizing the light in your photos.

As being either fill or key, and then determining whether you need more of one or the other. As you practice these concepts with your flash, you should find yourself beginning to conceptualize light in a different way. Fill and key are powerful concepts, and we'll be building our understanding of flash within the framework of light is fill or light is key.