What is incident light metering?
Incident light metering measures the light falling on a subject, rather than the light reflecting off it. The photographer holds a handheld light meter at the subject’s position, points the meter’s white dome toward the camera, and takes a reading. The meter then suggests an exposure.
“Incident light” simply means light that arrives at a surface. A light meter, in general, is a device that measures light and converts it to an exposure value or a combination of aperture, shutter speed and ISO.
Reflected metering: what your camera does
Your camera’s built-in meter is a reflected-light meter. It measures the light bouncing off the scene back toward the lens. That reading depends on two things: how much light is falling on the scene and how reflective the scene is.
This is the weakness of reflected metering. A white shirt and a black shirt in the same light reflect very different amounts of light, so the camera will want to expose them differently, trying to turn each into a midtone. That is why snow tends to look gray and black cloth tends to look washed out unless you apply exposure compensation. For more on that behavior, see our guide to camera metering modes.
Why incident metering avoids that problem
Because an incident meter reads the light falling on the subject, it does not care whether the subject is light or dark. A white dress and a black suit in the same light get the same reading. If you expose according to that reading, light subjects tend to render light and dark subjects tend to render dark, which is usually what you want.
This often makes incident metering more consistent across a series of shots, and helpful when you are working with studio flash, film or video, where repeatable exposure matters.
Dome, plate and other diffusers
Handheld meters typically use a translucent diffuser over the sensor. Common types include:
- White dome: the standard for incident metering. It collects light from a wide angle and approximates how a three-dimensional subject receives it.
- Flat disc or plate: used for measuring light from a particular direction, such as a single flat-lit surface, and sometimes for contrast checks.
- Reflected attachments or spot optics: some meters have a lens or a viewfinder for reflected readings, which behave like a camera’s spot meter.
Terminology and accessories differ by manufacturer, so check your meter’s manual.
How to take an incident reading
- Set the meter to the same ISO as your camera and, if relevant, the shutter speed you plan to use (or the aperture).
- Stand where the subject is, holding the meter close to the subject.
- Point the dome toward the camera position. In many portrait setups, this is the common approach.
- Press the measurement button and read the suggested aperture or shutter speed.
- Dial those settings into the camera in manual mode.
- Take a test shot and check the histogram.
For flash, many meters can read a flash burst, either with a cable or wirelessly, which is difficult to do with a camera’s own meter in advance.
Neutral gray and calibration
Reflected meters are calibrated to render the measured area as a mid-gray. A gray card, which reflects a standard portion of the light, lets you measure that gray with your camera’s meter under the same light as the subject. This gives a result close to an incident reading, and it is a low-cost alternative when you do not own a handheld meter.
Bear in mind that different meters and cameras may have slightly different calibrations, so it is worth comparing your meter against your camera on a few test shots.
When incident metering falls short
- You need access to the subject’s position. For distant subjects such as wildlife or a landscape, you cannot hold a meter there, and an in-camera meter is the practical option.
- If the lighting at the subject’s position differs from the lighting at the camera, the reading may not apply.
- Very bright backlight, glints or highlights that you want to protect still need judgment and a look at the histogram.
- A handheld meter is an extra piece of kit to buy, carry and learn.
In-camera spot meters versus handheld meters
A spot meter in your camera measures reflected light from a small area and works well for distant subjects. A handheld incident meter reads light at the subject. Many experienced photographers use both: incident for controlled settings, spot for checking specific tones such as the brightest highlight or a face. See high-key and low-key photography for cases where you deliberately deviate from a “normal” reading.
Common questions
What is the difference between an incident and a reflected light meter?
An incident meter measures light falling on the subject, while a reflected meter measures light coming from the subject. Incident readings are independent of subject brightness.
What is incident light?
It is the light that strikes a surface, as opposed to the light reflected from it.
What is the definition of a light meter in photography?
A light meter is a device, or a part of a camera, that measures light and turns that measurement into exposure settings.
Key takeaways
- Incident metering reads the light on the subject, so subject color and tone do not skew the result.
- Camera meters are reflected, which is why they need compensation on very light or dark scenes.
- A gray card with your camera’s meter is a budget alternative that approximates an incident reading.