Page "Light meter" Paragraph 13

Another way to avoid under-or over-exposure for subjects with unusual reflectance is to use a spot meter: a reflected-light meter that measures light in a very tight cone, typically with a one degree circular angle of view.

An experienced photographer can take multiple readings over the shadows, midrange and highlights of the scene to determine optimal exposure, using systems like the Zone System.

Many modern cameras include sophisticated multi-segment metering systems that measure the luminance of different parts of the scene to determine the optimal exposure.

When using a film whose spectral sensitivity is not a good match to that of the light meter, for example orthochromatic black-and-white or infrared film, the meter may require special filters and re-calibration to match the sensitivity of the film.