A reader writes: “I’ve heard the term “Ambient Light” used by photographers and know it’s important, but I only have a vague notion about what really it means. Can you give me a clear explanation.”
Let me shed some light on the term “Ambient Light” and its importance in photography.
Ambient light is the light that exists in a scene. Also referred to as “natural light” or “existing light,” ambient light can be the found light inside a home, a restaurant or concert hall, or a bright, sunny day, a deep foggy day, a city at night...in other words, any kind of pre-existing light. This is found light, not additional light that you, the photographer, might choose to add, such as flash. When photographing a scene that is lit with any kind of ambient light, you need to use a light meter to determine exposure.
The ambient light here is produced by a heavy fog. It’s a neutral, diffused light.
Exposing for ambient light
The most common exposure method is via your camera’s built-in exposure meter. When shooting with a compact camera, determining exposure and setting the camera’s aperture, shutter speed and (in some cases) ISO happens automatically. With DSLRs, this also can happen when the camera is in Program or “green” mode, but you have plenty of other exposure mode options. You can have more control over exposure by choosing Aperture-Preferred, Shutter-Preferred, or Manual exposure modes. A less-common approach is to use a handheld meter, which measures light and provides exposure setting guidance.
When metering a scene, a light meter averages out the entire scene to 18% gray. If the scene has a lot of bright areas, the meter might be misled into reading a darker exposure to compensate for all of the bright. To fix this, you need to increase the exposure by choosing a longer exposure or wider aperture. A darker scene may force the camera and meter to default to a longer exposure as it fights to render the darker colors closer to 18% gray. To compensate, you would decrease the exposure by either choosing a faster shutter speed or a smaller aperture.
The most common kind of meter is a reflected light meter, which is the kind found on cameras and most handheld meters. This meter reads light reflected off the subject, and it’s the kind of meter that is most easily misled when there are extremes of light or dark in a scene.
In this photo, the ambient light source is the sun, which is casting strong shadows in this photo of a rest stop off the Florida Turnpike near sunset. The camera’s internal light meter was used to determine exposure, which was set manually.
One way to get an accurate meter reading of ambient light is to use an incident light meter, which is a handheld meter that reads the source of the light. A white dome is placed over the light receptor and the meter provides an accurate reading based on the light that hits it.
Mark Wallace explains what settings to use to get the right exposure:
Types of ambient light and white balance
While a major component of ambient light is exposure, another key aspect is the color of light, or color balance, which is determined by the light source. The major sources of light are the sun (either a bright sunny day, referred to as “Daylight”, which is slightly more blue, or a cloudy day), tungsten light, which is most commonly found in homes, fluorescent light, which can be found in homes or businesses, and sodium-vapor light which is often used in streetlights and in stadiums.
The ambient light for this image was provided by two sources: An incandescent lamp, which is beyond the right edge of the photo, and a computer screen which is casting a somewhat bluer light on the girl’s face. In this case, the camera’s auto white balance did a good job producing a natural-looking shot despite the mixed light sources.
Each light source has its own color hue, which is more visible to sensors in digital cameras and film than to the human eye, which automatically compensates. Digital cameras have White Balance settings to record light to look as neutral as possible. Auto White Balance is the default on all digital cameras and that will work fairly well.
When shooting in ambient light, the light sources may all be the same, or they may be mixed. While the human eye can automatically compensate for the differences in color cast produced by each kind of light source, film and a digital camera’s sensor can’t. Advanced digital cameras can let you create a custom white balance, which is ideal for such situations. However, some photographers simply shoot using Auto White Balance and use the variety of color hues in a scene as a creative element.
Ambient Light and Flash
When shooting with a flash, the exposure of the bright short-duration light can overwhelm the ambient light. Without correction, rooms that may be brightly lit can be rendered black. However, it is possible to increase exposure or decrease flash power on more advanced cameras (or when using an external flash) to balance ambient and flash light for a more natural look.
Conversely, you may wish to use a flash in bright daylight to lighten shadows falling on your subject, as in the photo at right. In this case, flash power may need to be increased to match the brightness of the scene. In either case, you use a light meter to determine the ambient light exposure, and a flash meter (or rely on your camera’s TTL flash) to determine a balanced flash exposure.
For more on balancing flash with ambient light, check out this video on AdoramaTV:
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