Light Meter is a handheld tool that photographers use to measure the light intensity in a given scene. Using a light meter, a photographer can determine the film speed and shutter speed he will need to ensure that his film receives the proper exposure. The most common light meters use selenium, silicon or CdS (Cadium Sulfide) sensors. While selenium sensors generate power from the light meter, both silicon and CdS sensors require batteries.
Light meters are important tools in both photography and cinematography, as the clarity of a picture greatly relies on the appropriate light for a scene.
Metering light can take occur in two different manners, either reflective or incident. As the name suggests, reflective light metering works by measuring light as it is reflected off of the main subject.
While reflective metering tools are effective for subjects at a distance, they can be problematic if a subject is extremely light or incredibly dark: light objects will reflect more light, and dark ones will reflect less. Consequently, this method can produce inaccurate reads of light intensity. Nevertheless, reflective light meters are usually built into most modern cameras.
Conversely, incident light metering registers the amount of light that falls on the object. Handheld light meters function through the incident method. Although this method is more accurate by ignoring reflective errors, incident metering can only happen if a photographer can get up close to his subject. Similarly, because incident light metering requires that a photographer buy extra equipment, it is a more expensive way to measure light intensity.