Light Metering Quiz: Incident vs Reflected and Zone System

A reflected meter, like the one built into the camera, measures the light bouncing off the scene toward the camera. Because it depends on how light or dark the subject is, it can be fooled by snow or black objects.

An incident meter is held at the subject's position, pointing back toward the camera or light, and measures the light falling on the subject. It ignores how light or dark the subject is, giving an accurate exposure for the light itself.

A reflected meter reads the light bouncing off the scene. Very bright subjects reflect more light than average, prompting the meter to reduce exposure; very dark subjects reflect less, prompting the meter to increase it. Both responses aim at the same middle-gray target regardless of subject brightness.

An incident meter measures the light falling on the subject, not the light reflected from it. That means a white dress and a black suit in the same light get the same correct reading, without the meter guessing.

In a studio, photographers control each light and need precise readings of light falling on the subject. A handheld incident meter measures each light and its ratios accurately, which matters for flash setups and consistent results.

Camera meters are calibrated to render any metered area as middle gray, which has a reflectance of approximately 18 percent. This works well for average scenes but consistently produces incorrect exposures for subjects that are significantly lighter or darker than middle gray.

Specular highlights are bright, mirror-like reflections of the light source itself on shiny surfaces such as eyes, metal or water. They are much brighter than the diffuse light from matte surfaces and often clip to pure white.

A specular highlight is far brighter than the rest of the scene. If you spot meter it, the meter tries to render it as middle gray, which darkens the whole exposure by several stops.

In the zone system, the photographer decides which important tone in the scene should fall on a specific zone, then adjusts exposure to achieve that placement. Everything else in the scene falls on its corresponding zone relative to that choice.

In steady light, metering the skin and applying a known offset gives a consistent result. For example, light skin is often about one stop brighter than middle gray, so adding about one stop corrects for that.

Exposure value is a single number for all combinations of shutter speed and aperture that give the same exposure. EV 15 at ISO 100 covers f/16 at 1/125, f/11 at 1/250 and f/8 at 1/500. Each step of 1 EV is one stop.

Sunny 16 states that in bright sun, a correct exposure is achieved at f/16 with a shutter speed equal to 1/ISO. It is a mental shortcut that lets photographers verify or set exposure without a meter in clear daylight conditions.

Every scene the meter evaluates gets rendered as a middle gray average, regardless of its actual brightness. A white wall looks gray and a black wall looks gray in the metered result, which is why exposure compensation is needed to preserve both.

In a backlit scene, a reflected meter is dominated by the bright background and underexposes the subject. An incident meter at the subject's position measures only the light falling on the subject's face, giving the correct exposure for the subject.

A light meter measures light and suggests exposure settings, often expressed as an EV. It has no way to judge whether the subject is in focus.