tmeter built into your video camera that will read the amount of light in the frame of your camera. But what part of the frame? Most cameras don't allow "spot metering", which gives you the ability to measure different sections of the frame for differences between light and dark.
The most important thing to remember here is that your video camera can only handle so much contrast between light and dark. It’s your job as the DP (director of photography) to control and mold that light to your purposes. The purpose of the light meter is to tell you what kind of lighting conditions you are dealing with. A handheld light meter that is separate from the camera will provide you with a tool that will allow you to get accurate readings from anywhere in the frame and let you make decisions about how you want to handle those conditions.