A light meter is a device that measures the intensity of light in a scene and provides exposure settings to achieve a correct exposure. Every digital camera has a built-in light meter that continuously reads light levels and informs the camera’s automatic and semi-automatic exposure modes. External handheld light meters are also used by photographers who want more precise control, particularly in studio and film photography.
Built-In vs. Handheld Light Meters
Your camera’s built-in meter is a reflected light meter. It measures the light bouncing off the subject and back toward the camera. This is convenient because it reads the actual scene you are photographing through the lens. However, reflected meters can be fooled by subjects that are unusually bright or dark, because they assume the scene averages to a middle gray tone.
Handheld light meters can measure incident light, which is the light falling onto the subject rather than reflecting off it. You hold the meter at the subject’s position, pointing it toward the camera, and it reads the light arriving from the light sources. Incident metering is not affected by the subject’s brightness or color, making it more accurate for consistent exposures across different subjects in the same light.
How Camera Metering Modes Work
Built-in meters offer several metering modes that change how they read the scene. Evaluative (or matrix) metering divides the frame into zones and analyzes brightness across the entire scene. Center-weighted metering prioritizes the middle of the frame. Spot metering reads a very small area, typically 2-5 percent of the frame, giving you precise control over which part of the scene determines the exposure.
Reading the Meter
In manual mode, your camera displays a meter indicator showing whether the current settings will produce an underexposed, correctly exposed, or overexposed image. The display typically shows a scale from -3 to +3 stops, with a marker that moves left (dark) or right (bright) as you adjust aperture, shutter speed, or ISO. Centering the marker produces what the camera considers a correct exposure, though you may intentionally shift it for creative reasons.
When to Use a Handheld Meter
Handheld meters remain popular in studio photography, where precise control of multiple light sources is essential. They are also valuable for film photography, where you cannot review exposures on a screen after each shot. For digital photographers working in natural light, the camera’s built-in meter combined with the histogram provides all the information needed for accurate exposure in most situations.