Keep the Light Source In Front of the Subject: The main source of light should be coming from somewhere over the cameraperson’s shoulder and falling on the subject’s face rather than on the back of the subject’s head. You also don’t want your subject standing directly under an overhead light or the sun because the shadows under the chin will be too severe. The light should fall on the face at an angle.
Unless you’re using a light kit, chances are you will have only a limited amount of control over the angle of the light. Do your best. 45 degrees is a good angle to try and achieve because it reminds us of the angle of the sun, which falls at an angle somewhere between 30 and 45 degrees for much of the day. If you’re shooting outside under a clear sky with the sun high, right above or nearly above your subject, consider shooting in the shade. This will cut back on the shadows under the eyes and chin.
Avoid Backlighting: You don’t want the source of light to come from behind your subject. If your subject is standing in front of a window or even a white wall, your subject may appear dark, perhaps even in silhouette. This is called backlighting. Backlighting can be a good effect if you want to hide someone’s identity, but otherwise it should be avoided.
You might not notice a slight or moderate backlighting problem while you’re shooting because our eyes, unlike the camera, make adjustments for shadows. What has happened is that the light meter in your camera has judged the light being reflected throughout the entire frame and not just the light being reflected off your subject. When much of the frame is filled with something that reflects a whole lot of light, like a white wall or a bright sky, then you can’t trust your automatic exposure. Chances are good that the contrast between your subject and the background is too great.
To fix this, you can set the exposure manually or, if your camera has one, use the backlight feature in the on-camera menu. The backlight feature essentially opens the iris wider so that the subject in the foreground is exposed correctly. Another quick fix is to zoom in on your subject, after the auto-exposure has reset itself for the closer shot, lock the exposure by switching into manual exposure mode (most consumer-grade video cameras work this way), then zoom out to set up your shot.
This works if your subject is mid-toned. Rule of thumb says that Caucasian skin tones are exposed correctly at one stop above medium gray. So, when you switch into manual, open up one stop and the skin tone of your Caucasian subjects should come out appropriately pink or beige rather than gray. For someone with dark skin, close the aperture down a stop or two before locking the exposure and zooming out. If you’d prefer not to guess, set the exposure based on a gray card.
The above steps will allow you to expose your subject correctly, but you also risk overexposing the rest of the frame. Generally, this is preferable to underexposing your subject, but it’s not necessarily your best option. Whenever possibly, you should avoid backlighting by setting up a better shot.
To avoid backlighting, don’t allow the subject of your shot to stand with his or her back to the light. If you’re indoors and you’re using a window for light, you want the subject facing the window rather than standing with their back to it. Try not to shoot your subjects in front of a white or off-white wall. Try to shoot your subject in front of a background that is either mid-toned or has a fairly wide range of tonal qualities rather than a white or off white wall. Ideally, you won’t put them in front of a wall at all; instead shoot them in front of a scene that stretches into the distance. This will give your shot some depth, de-emphasizing the two-dimensional nature of video. If you’re shooting outside, make sure it’s the subject and not the cameraperson who faces the sun
Finally, if you can’t do any of those things, if you’re shooting a speaker or a staged event for example, move in for a close-up or medium shot of your subject and shoot that way. If you fill the frame with your subject rather than a bright background, then your camera’s light meter will do a better job of setting the exposure. You may not need to adjust manually or use the backlight feature at all. Filling the frame with the subject also takes away any confusion your audience may have about what it’s supposed to focus on.