LIGHT METERS
Light meters (also known as exposure meters) are
used to determine the amount of light needed for
a given photographic exposure. In many cameras,
light meters are often built into the body, and
can be made to automatically set the exposure.
Handheld light meters are used with cameras
without built-in meters, as well as for special me-
tering applications.
The amount of exposure needed on film is deter-
mined by the film speed or sensitivity. The light
meter is set to this speed to determine the aperture
and shutter speed combination that will result in
the appropriate amount of density on film. The
light meter measures the light intensity of the
scene, and then calculates the needed exposure
based on the film speed. This exposure is most
often given in terms of aperture and shutter speed
settings, but can also be rendered in exposure
values (EV).
Exposure is a combination of the intensity of the
light that reaches the film, and the length of time
that light strikes the film. Exposure can be
increased and decreased by controlling these two
factors. These are controlled by changing the aper-
ture, which controls the brightness, and by chan-
ging the shutter speed, which controls the time.
Light meters measure the brightness value of a
scene based on the assumption the scene has an
average distribution of highlights, midtones, and
shadows. The average of these tones is a medium
gray, also known as 18% gray. All light meters,
regardless of function, rely on 18% as the standard.
Types of Light Meters
The most common form of light meter is the
reflected light meter. These meters are most com-
monly built into camera bodies, but all handheld
meters also have reflected metering capability.
Reflected meters measure the amount of light
being reflected off of the subject and the scene. To
take a reflected meter reading, the meter (or the
camera) is pointed at the subject or scene to be
metered. The meter will then provide readings that
will render that scene to the 18% gray standard.
A variation of reflected light meters is the spot
meter, which takes a meter reading in a highly spe-
cific area, usually about .5–3of the total scene (as
opposed to the 30–50 reading of a standard
reflected light meter). Spot meters can be built into
a camera system or into handheld meters.
Handheld light meters often have the additional
capability of taking incident meter readings. Inci-
dent meters evaluate the amount of light falling on
the subject. In this manner, the subject’s original
reflectance values are irrelevant. To take an inci-
dent meter reading, the meter is brought to the
position of the subject (so that the light falling on
the meter is identical to that falling on the subject)
and the meter is pointed back toward the lens of the
camera. Incident meters use a white dome for a
reading, which results in a very wide angle of view
(180). The metered value is calibrated to the 18%
gray standard, but it is the light falling on the
subject that is placed at this value.
Flash meters are designed to take a light meter
reading in the brief burst of light caused by a flash
discharge. Flash meters are most often of the hand-
held variety, and are often capable of both reflected
and incident flash meter readings.
Color temperature meters are designed to mea-
sure the color temperature of a given light source.
Color temperature results in a particular color cast
on film that is often not easily detected by the
human eye. For example, fluorescent light sources
look white to our eye, but render with a greenish
cast on film. As every light source has a different
color temperature, color temperature meters pro-
vide a measurement of that value so that it can be
corrected by use of filters while shooting.Middle Gray
A light meter, regardless of type, assumes that
every light source and subject is middle gray, or
18% gray. The 18% gray value is the average of all
the possible tones in an image. The assumption that
the scene is ‘‘average’’ works fairly well the major-
ity of the time. However, in instances where the
scene is not ‘‘average,’’ as in an example of a
white horse in a field of snow, the meter will render
the scene improperly when it places it to 18% gray.
The result is a muddy, gray horse and field instead
of the white with detail of the original scene. TheLIGHT METERS