Sequence viewing > Photographic Exposure - Resource - © Lloyd Godman

What is a light meter?

Taking more accurate exposure readings is done with a light meter. 
All meters work on this basis of converting light into electric current, which can then be measured on a scale and translated into appropriate shutter speeds and f numbers relative to the film ASA. 
While some meters work on this basis of converting light into electric current like a solar panel, others have a battery which provides power to a Cds or Cadmium sulphide cell which are photo-resistance; meaning that its electrical resistance changes in proportion to the light it receives. 
 

Selenium Cell Meters

Selenium Cell meters were also built into some cameras. The cell was facing the same direction as the lens, and there was a dial on the top of the camera which was rotated to align the two needles and then the shutter / aperture combinations transferred to the camera.

 

As camera construction became more sophisticated, the meter functions were coupled directly to the aperture and shutter.

 

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Historic Light meters 

 

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