A light meter is a device used to measure the amount of light

Light

Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...

. In photography

Photography

Photography is the art, science and practice of creating durable images by recording light or other electromagnetic radiation, either electronically by means of an image sensor or chemically by means of a light-sensitive material such as photographic film...

, a light meter is often used to determine the proper exposure

Exposure (photography)

In photography, exposure is the total amount of light allowed to fall on the photographic medium during the process of taking a photograph. Exposure is measured in lux seconds, and can be computed from exposure value and scene luminance over a specified area.In photographic jargon, an exposure...

 for a photograph. Typically a light meter will include a computer, either digital

Digital

A digital system is a data technology that uses discrete values. By contrast, non-digital systems use a continuous range of values to represent information...

 or analog

Analog computer

An analog computer is a form of computer that uses the continuously-changeable aspects of physical phenomena such as electrical, mechanical, or hydraulic quantities to model the problem being solved...

, which allows the photographer to determine which shutter speed

Shutter speed

In photography, shutter speed is a common term used to discuss exposure time, the effective length of time a camera's shutter is open....

 and f-number

F-number

In optics, the f-number of an optical system expresses the diameter of the entrance pupil in terms of the focal length of the lens; in simpler terms, the f-number is the focal length divided by the "effective" aperture diameter...

 should be selected for an optimum exposure, given a certain lighting situation and film speed

Film speed

Film speed is the measure of a photographic film's sensitivity to light, determined by sensitometry and measured on various numerical scales, the most recent being the ISO system....

.

Light meters are also used in the fields of cinematography

Cinematography

Cinematography is the making of lighting and camera choices when recording photographic images for cinema. It is closely related to the art of still photography...

 and scenic design

Scenic design

Scenic design is the creation of theatrical, as well as film or television scenery. Scenic designers have traditionally come from a variety of artistic backgrounds, but nowadays, generally speaking, they are trained professionals, often with M.F.A...

, in order to determine the optimum light level for a scene.