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What Is a Light Meter For?
by Kandra Sperling
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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.
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Meters fall into two basic categories. Reflected-light meters measure the light reflected from the subject or scene. They are also referred to as averaging meters. Incident-light meters measure light that falls onto your subject or scene. Within these two categories, there are in-camera meters and handheld meters, both of which may be one of various types of meters for specific uses, such as matrix meters and spot meters.
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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.
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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.
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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.
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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.
