Light meter

exposure metermeteringExposure meter calibrationlux meterluxmeterCdS light meterISO 2721light metering devicelight metering systemlight-meter
A light meter is a device used to measure the amount of light.wikipedia
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Film speed

ISOISO sensitivityASA
Typically a light meter will include either digital or analog electronic circuit, which allows the photographer to determine which shutter speed and f-number should be selected for an optimum exposure, given a certain lighting situation and film speed.
GOST markings are only found on pre-1987 photographic equipment (film, cameras, lightmeters, etc.) of Soviet Union manufacture.

F-number

focal ratioaperturef-stop
Typically a light meter will include either digital or analog electronic circuit, which allows the photographer to determine which shutter speed and f-number should be selected for an optimum exposure, given a certain lighting situation and film speed.
T-stops are sometimes used instead of f-numbers to more accurately determine exposure, particularly when using external light meters.

Exposure (photography)

exposureexposuresoverexposure
In photography, a light meter is often used to determine the proper exposure for a photograph.
"Manual" exposure calculations may be based on some method of light metering with a working knowledge of exposure values, the APEX system and/or the Zone System.

Galvanometer

tangent galvanometernull detectorgalvanoscope
They indicate the exposure either with a needle galvanometer or on an LCD screen.
Galvanometers also had widespread use as the visualising part in other kinds of analog meters, for example in light meters, VU meters, etc., where they were used to measure and display the output of other sensors.

Selenium

SeSe 3 selenium poisoning
Later meters removed the human element and relied on technologies incorporating selenium, CdS, and silicon photodetectors.
This phenomenon was used in the design of light meters and similar devices.

Camera

camerasWebcamexposure control
Many modern consumer still and video cameras include a built-in meter that measures a scene-wide light level and are able to make an approximate measure of appropriate exposure based on that.

Zone System

average luminancethe Zone System
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.
Exposure is often determined using a reflected-light exposure meter.

Minolta

Chiyoda KogakuChiyoda Kogaku Seikō KKChiyoko
Sekonic ) and 14 (Minolta, Kenko, and Pentax); the
1966: The Minolta SR-T 101 SLR camera is one of the first with TTL (through-the-lens) full aperture light metering. The first is Topcon RE Super from 1963.

Gray card

sometimes is made of a neutral test card, or gray card.
A gray card is a middle gray reference, typically used together with a reflective light meter, as a way to produce consistent image exposure and/or color in film and photography.

Selenium meter

selenium light meterselenium cellselenium lightmeter
Selenium meter
The most common use of such light meters is measuring the exposure value for photography.

Exposure value

EVstopscamera exposure
EV.
K is the reflected-light meter calibration constant

Photometer

luminometerastrophotometerflame-photometers
Photometer | Photodetector
Historically, a photometer was separate from the camera and known as an exposure meter.

Photography

photographerphotographicphotographs
In photography, a light meter is often used to determine the proper exposure for a photograph.

Digital data

digitaldigital informationdigitally
Typically a light meter will include either digital or analog electronic circuit, which allows the photographer to determine which shutter speed and f-number should be selected for an optimum exposure, given a certain lighting situation and film speed.

Analog computer

analogue computeranaloganalog computers
Typically a light meter will include either digital or analog electronic circuit, which allows the photographer to determine which shutter speed and f-number should be selected for an optimum exposure, given a certain lighting situation and film speed.

Shutter speed

exposure timeexposure timesshutter speeds
Typically a light meter will include either digital or analog electronic circuit, which allows the photographer to determine which shutter speed and f-number should be selected for an optimum exposure, given a certain lighting situation and film speed.

Cinematography

cinematographercinematographiccinema
Light meters are also used in the fields of cinematography and scenic design, in order to determine the optimum light level for a scene.

Scenic design

set designerset designstage designer
Light meters are also used in the fields of cinematography and scenic design, in order to determine the optimum light level for a scene.

Architectural lighting design

architectural lightinglighting designlighting engineer
They are used in the general field of architectural lighting design to verify proper installation and performance of a building lighting system, and in assessing the light levels for growing plants.

Refractive index

index of refractionrefractive indicesindices of refraction
The earliest type of light meters were called extinction meters and contained a numbered or lettered row of neutral density filters of increasing density.

Neutral-density filter

neutral density filterneutral densitygray filter
The earliest type of light meters were called extinction meters and contained a numbered or lettered row of neutral density filters of increasing density.

Luminosity function

amount of lighthuman eyehuman perception of brightness
Extinction meters suffered from the problem that they depended on the light sensitivity of the human eye (which can vary from person to person) and subjective interpretation.

Cadmium sulfide

CdSsulfideA 2 B 5
Later meters removed the human element and relied on technologies incorporating selenium, CdS, and silicon photodetectors.

Silicon

SisiliciumSilicon (Si)
Later meters removed the human element and relied on technologies incorporating selenium, CdS, and silicon photodetectors.

Photodetector

photocellAmbient lightAmbient light sensor
Later meters removed the human element and relied on technologies incorporating selenium, CdS, and silicon photodetectors. Photometer | Photodetector