What is the purpose of a light meter, and when should a photographer use it on a commercial shoot?

• A. To measure light intensity for exposure; use for manual exposure control, especially with strobes or mixed lighting for consistency.
• B. To measure color temperature of lights.
• C. To calibrate camera autofocus.
• D. To determine lens focal length.

Answer: (D)

A light meter is used to measure light intensity so you can set exposure precisely. On a commercial shoot, you want consistent results across multiple shots and lighting setups, especially when you’re using strobes or mixing lights. A handheld meter helps you quantify how bright the scene is and translate that into camera settings (aperture, shutter, ISO) to hit a target exposure without guessing.

You’ll typically use incident metering (measuring the light falling on the subject) to get exposure that’s not biased by the subject’s reflectivity, or spot metering to read brightness from a specific area you intend to expose correctly. This is particularly valuable when balancing ambient light with flash or when you need to reproduce the same exposure across many images or locations.

Color temperature, autofocus calibration, and lens focal length aren’t the primary purposes of a light meter, which is why its main use is exposure control rather than those other functions.