Light meter is an instrument used to measure the brightness of light. Light meters serve many purposes. People can use them to set an appropriate level of artificial light for growing plants or performing certain tasks safely. Light meters called exposure meters help photographers choose the best camera settings for taking a photograph.
Light meters use a device called a sensor that reacts to changes in the brightness of light. Many light meters use a sensor called a cadmium sulfide photocell attached to a battery. Electric current flows more easily through the photocell as the amount of light striking its surface increases. The light meter measures the current flowing through the photocell to calculate the amount of light falling on the sensor.
Another type of light meter uses a sensor called a silicon photodiode. The photodiode produces a weak electric current when light strikes its surface. The light meter amplifies and then measures the current to determine the amount of light falling on the sensor. A silicon photodiode responds quickly to changes in the brightness of light. It can even measure the light given off by the firing of a camera flash.
Many cameras feature built-in light meters. A built-in light meter measures the amount of light entering the camera lens from the center of the scene being photographed. The camera can then automatically adjust its settings to produce a good exposure using the available light. Some cameras have meters that measure the brightness of several different areas of the scene being photographed. These cameras can adjust their settings to achieve an even balance between light and dark areas in the same photograph.
Some light meters express brightness in terms of foot-candles, lumens, luxes, or other units. Many exposure meters use units chosen to correspond with camera settings.
See also Light (Energy and brightness) ; Photography (Exposure meters) .
