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A light meter is a type of photographic equipment used to ensure accurate exposure of images. By measuring the intensity and reflectivity of lighting conditions, a light meter tells a photographer or camera operator how to set the camera to receive the best image. A light meter may be built in, as in many digital cameras, or may be a handheld device more often seen in professional photography and film work.
Light meters can give several different readings, depending on the specifications of the device. Some meters measure only the light falling on an object, while others factor in the reflective value of the object into lighting calculations. For instance, if in a dim room there is a white wall and a black wall, the light falling on both may be equal. Because white is more reflective than black, however, a light meter that measures reflectivity will adjust the reading for different surfaces, allowing the camera person to set the camera more accurately. Light meters that measure only falling light are usually called incident meters, while models that calculate in reflectivity are called reflectance meters.
Most digital cameras include light meters as built-in components. If a camera is set on automatic, the meter will kick in to measure the light in the frame before snapping the picture. Most built in meters sample the entire area of the frame and use an average value to set the camera. Professionals tend to prefer a spot meter, which can measure the light of each specific object in a frame.
Whether built in or as an accessory device, the information given by light meters is used to determine a camera's F/stop setting. The F/stop determines the diameter of the lens opening, which controls how much light passes through the lens. A high F/stop setting indicates that the shot is brightly lit, so the diameter of the lens must be reduced to prevent too much light from passing through and overexposing the image. Conversely, a low F/stop setting means that more light is needed to expose the image, requiring the lens to open farther to allow more light to pass through to prevent underexposure.
To purchase a light meter, contact professional camera suppliers or reputable online dealers. Remember that many modern cameras do include an area light meter that will give general settings for exposure. Most cameras also include a manual setting that permits F/stop adjustment for more advanced users. For professional work in film or photographer, a more specific light meter may be required for superb images. Investing in a professional light meter is highly recommended by experts for anyone who plans to make a career out of photography or film.