Editing Light meter (section)

===Photoelectric types===
[[File:Gossen Lunasix 3 front.jpg|thumb|upright|Gossen Lunasix 3 (in US: Luna Pro S) using {{chem|Cd|S|link=Cadmium sulfide}} photoresistor with analog readout; available from 1961 to 1977]]
Starting in 1932,<ref>{{cite book |url=https://archive.org/details/guideperfectexpo0000unse/page/20/mode/2up |title=Guide to Perfect Exposure |first1=George B. |last1=Wright |first2=Cora |last2=Wright |edition=Fourth |publisher=Chilton Book Company |location=Philadelphia |date=1967 |url-access=registration |lccn=67-17795}}</ref>{{rp|20}} electronic light meters removed the human element and relied on technologies incorporating (in chronological order) [[selenium]], [[Cadmium sulfide|CdS]] (1960s), and silicon ([[semiconductor]], 1970s) [[photodetector]]s.<ref name=Dunn-Wakefield-ch4>{{cite book |url=https://archive.org/details/exposuremanual0000dunn/ |title=Exposure Manual |chapter-url=https://archive.org/details/exposuremanual0000dunn/page/86/mode/2up |chapter=4: Photoelectric Reflected-light Meters |author1=Dunn, Jack F. |author2=Wakefield, George L. |edition=Third |date=1974 |publisher=Fountain Press |location=Hertfordshire, England |isbn=0-85242-361-6 |pages=87–121 |url-access=registration |access-date=8 September 2023}}</ref> Most modern light meters use silicon sensors.<ref name=Hicks99>{{cite book |url=https://archive.org/details/perfectexposuref0000hick/ |chapter-url=https://archive.org/details/perfectexposuref0000hick/page/88/mode/2up |title=Perfect exposure: from theory to practice |chapter=7: Exposure Meters |last1=Hicks |first1=Roger |last2=Schultz |first2=Frances |date=1999 |pages=88–103 |publisher=David & Charles |isbn=0-7153-0814-9 |url-access=registration}}</ref>{{rp|91}} They indicate the exposure either with a needle [[galvanometer]] or on an [[LCD]] screen.

Selenium light meters use sensors that are [[photovoltaic]]: they ''generate'' a voltage proportional to light exposure. Selenium sensors generate enough voltage for direct connection to a meter; they need no battery to operate and this made them very convenient in completely mechanical cameras.<ref name=Clerc70/>{{rp|416}}<ref name=Dunn-Wakefield-ch4/>{{rp|87–88}} Selenium sensors however cannot measure low light accurately (ordinary lightbulbs can take them close to their limits) and are altogether unable to measure very low light, such as candlelight, moonlight, starlight etc.<ref name=Focal78/>{{rp|56}}

CdS light meters use a [[photoresistor]] sensor whose electrical resistance decreases proportionately to the intensity of light exposure. These require a battery to operate,<ref name=Dunn-Wakefield-ch4/>{{rp|89–90}} but are significantly more sensitive to low light, able to detect lighting levels approximately {{frac|100}} of the lower sensitivity limit of selenium cells.<ref name=Clerc70/>{{rp|417}} However, CdS sensors fell out of favor due to their slower response and extended sensitivity to red and infrared wavelengths.<ref name=Clerc70/>{{rp|417}}<ref name=Focal78/>{{rp|58}}

Semiconductor sensors are also photovoltaic, but the voltage generated is much weaker than selenium cells and semiconductor-based light meters need an amplification circuit and therefore require a power source such as [[battery (electricity)|batteries]] to operate. These are usually named after the materials and filtration used to ensure the spectral response is similar to the human eye or photographic film, such as '[[Silicon]] Blue Cell' (SBC) or '{{chem|Ga|As|link=Gallium arsenide}}'.<ref name=Focal78>{{cite book |url=https://archive.org/details/focalguidetoexpo0000lync/ |title=The Focalguide to exposure |first=David |last=Lynch |date=1978 |publisher=Focal Press |isbn=0-8038-2364-9 |url-access=registration}}</ref>{{rp|59}}

[[File:Autoexpmeter.JPG|thumb|left|An automatic light meter/exposure unit from an [[8mm film|8 mm]] [[movie camera]], based on a galvanometer mechanism (center) and a [[Cadmium sulfide|CdS]] [[photoresistor]], in opening at left.]]
Many modern consumer still and video [[camera]]s 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. Photographers working with controlled lighting and [[cinematographer]]s use handheld light meters to precisely measure the light falling on various parts of their subjects and use suitable lighting to produce the desired exposure levels.