0 a device for measuring how much light there is, especially when taking a photograph -- 曝光表，测光仪
Where will a light meter be placed?
To calibrate light meters, whether in a camera or hand held, the 18% gray card was conceived.
The visual system is not very good at being a physical light meter, but that is not its purpose.
The camera itself needed no batteries, though the prism light meter did (and of course the motor drive if added).
There are other types of specialized photographic light meters.
The camera had no light meter.
Built-in light meters and electronic shutters combined with microelectronics to make exposure control simpler and faster.
A selenium-cell powered light meter was cheaper in production and did not need a battery.
