A light meter is basically used to measure the intensity of light. They are used to determine the proper exposure for your photographs. They read the light and then give you the proper film speed and shutter speed to set your camera. The meter will also show the f-stop to use that will give you a neutral exposure of an ideal gray slate.
There are various systems of light meters used and the most common are selenium, CdS, and silicon meters. Selenium and silicon meters use photovoltaic sensors. These types of sensors will generate a voltage proportional to light exposure.
- Selenium sensors can generate enough voltage for direct connection to a meter.
- Silicon sensors need an amplification circuit and require batteries to operate.
- CdS light meters use photo resistance based sensors that also need batteries.
Silicon or CdS sensors are used in most modern meters. Many still and video cameras have built in light meters, but they are sometimes unreliable in certain situations.
Professional photographers and cinematographers usually use handheld ambient light meters. These meters can accurately measure the amount of light falling on various areas of their subjects. Light meters usually start at about $50.