What is a Light Meter?
Photographers capture light rather than the subject from which light reflects. A light meter measures a subject's luminosity by gauging either reflective light or by incident light methods. Light meters measure either reflected light or incident light. All light meters provide settings that equalize light values to middle gray.
Significance
Without an indication of a subject's brightness, a photographer cannot know what camera settings to use. Light meters measure the intensity of light that falls upon or reflects off of a subject. A photographer uses a light meter's exposure settings to adjust aperture and shutter speed. The information provided by a light meter is used as a factor to determine the lightness and darkness of a final print. The brightness value supplied by a light meter is not the same as an evaluation of a subject's lightness or darkness.
Types
There are two types of photographic light meters. Reflected-light meters measure how much light reflects from a subject. In-camera light meters are of the reflected-light variety. Hand-held meters can measure reflected light as well. Reflected-light spot meters determine exposure settings for light reflecting from specific areas rather than larger areas. Incident-light meters are always hand-held and measure the brightness of light that falls on a subject. Some meters are three-in-one, with reflected-light, incident-light, and spot meter functions.
Function
For either type of light meter, the initial step is to set the film speed into the meter. To use a reflected-light meter, either point the camera (in-camera meter) or the hand-held meter at the subject area. Obtain measurements for all areas of a subject. To use an incident-light meter, stand near the subject and point the meter at the camera. Use of incident-light meters is limited to subjects that are lit by an identical light source. It is difficult to use an incident-light meter when determining exposure for distant scenes.
Benefits
Photographers use different light meters depending upon subjects, such as landscapes or portraits, and depending upon the photographer's creative purpose. Reflected-light meters are most commonly used and provide exposure information for subjects with complex lighting. Incident-light meters indicate exposure that will apply for all areas of a scene. They also work well in controlled lighting situations.
Considerations
Light meters are calibrated to give exposure settings based on middle gray of the photographic gray scale. The exposure provided by a light meter is a starting point. If, for example, a photographer wants to capture the depth of a dark crevice in a sea cliff on a bright day, he must adjust aperture and shutter speed to create darkness and dimensionality. The photographer will use the light meter's reading to determine camera settings necessary for darker exposure. The same is true for especially light subjects. If one wants to communicate the ethereal glow of a mountain lit by the rising sun, one will adjust camera settings from the exposure provided by a light meter to expose more light to the film. Another consideration is that people normally see reflected light. Reflected-light meters give the best measurements for accurate representations of a subject or for a "normal" light measurement from which to begin the creative process.
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