What Is a Light Meter For?

Light meters are used to measure brightness or intensity of available or artificial light on or around a photographic subject. The reading from the light meter indicates what adjustments in auxiliary light, aperture or shutter speed may be needed in order to get the best possible exposure. With the advent of computer chips, automatic settings and digital photography, most cameras feature built-in light meters. Handheld light meters are still used, especially by studio portrait photographers.

In-Camera Meters

Most digital cameras feature more than one type of light meter, all of which fall into the reflected-light category. The Nikon D90 features a 3D color matrix meter that measures brightness, contrast and color in the widest area of your scene. In-camera, center-weighted meters evaluate the entire area of your scene, but place the most significance on the center of the frame. This meter is usually used in portraiture. In-camera spot meters analyze a small area of your focus point. This meter is usually used when your subject is off center.

Handheld Spot Meters

In a studio, where the camera is usually mounted on a tripod, a handheld meter is especially helpful, allowing for more exposure options. You can stand at your camera position aiming the meter at your subject to measure light reflected by your subject, or you can stand near your subject, aiming the meter at your camera to measure incident light. Handheld spot meters have a built-in viewing lens so you can see exactly which area of a scene you are metering. Like in-camera spot meters, handheld spot meters read light from only a small area, or "spot," of your scene.

Ambient Light Meters

When your image is underexposed, the image will be too dark. When it is overexposed, the image will be too light or washed out. An ambient-light or color-temperature meter analyzes existing, nondirectional light to help you get the correct white balance and exposure so the colors in your subject look natural. An ambient-light meter analyzes light and interprets the relative brightness of the light in order to produce what is referred to as a "middle tone." For subjects with high contrast, you will need to increase or decrease the meter reading by two f-stops.

Considerations

If you are an amateur photographer taking snapshots, a built-in light meter will be sufficient for a good reading. Light meters do not, however, read light exactly as your eyes and brain do. A professional photographer uses a light meter not necessarily to capture the scene as it is actually seen through his eyes, but to achieve a certain result, like create a silhouette of the subject.

Resources

• How Exposure Meters Work