photometer
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photometer
[fo-tom´ĕ-ter]1. a device for measuring the intensity of infrared, ultraviolet, or visible light.
2. a device for testing the sensitivity of the eye to light by determining the light minimum.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.
pho·tom·e·ter
(fō-tom'ĕ-tĕr),An instrument designed to measure the intensity of light or to determine the light threshold.
[photo- + G. metron, measure]
Farlex Partner Medical Dictionary © Farlex 2012
photometer
An instrument for measuring the luminous intensity of a light source or a surface, by comparing it with a standard source. The comparison can be done either with the human eye (as in the Lummer-Brodhun or SEI exposure photometers) or with a photoelectric cell (as in the Pritchard photometer). Syn. illuminometer; luxometer. See illuminance; luminance.
flicker photometer Visual photometer in which the observer sees a field illuminated alternately by two sources to be compared. When the sensation of flicker disappears, the intensity of the test source can be deduced by reading that of the reference standard source to which it is compared. For luminance difference, the frequency of alternation is chosen to be below the critical fusion frequency but for colour difference it is chosen above it. See critical fusion frequency.
Lummer-Brodhun photometer A cube in which two adjacent or concentric portions of a comparison viewing screen are separately illuminated by the test source and a standard source. The instrument gives quite accurate readings when the two sources are of identical colour.
Macbeth photometer Photometer using the Lummer-Brodhun cube, an eyepiece and a movable standard source illuminating a diffusing surface seen as an annulus by reflection within the cube. The portion of the source to be measured is seen through the cube as a spot within the annulus. The brightness of the annulus is adjusted until it matches that of the spot.
objective photometer See physical photometer.
physical photometer A photometer employing a radiant energy sensitive element (e.g. a photoelectric cell, a thermopile) and an intensity indicator. Example: Pritchard photometer. Syn. objective photometer.
Pritchard photometer See physical photometer.
SEI exposure photometer; subjective photometer See visual photometer.
visual photometer A photometer in which the equality of brightness of a light source or a surface with a comparison standard source is made by visual observation. Examples: flicker photometer; Lummer-Brodhun photometer; Macbeth photometer; SEI photometer. Syn. subjective photometer.
flicker photometer Visual photometer in which the observer sees a field illuminated alternately by two sources to be compared. When the sensation of flicker disappears, the intensity of the test source can be deduced by reading that of the reference standard source to which it is compared. For luminance difference, the frequency of alternation is chosen to be below the critical fusion frequency but for colour difference it is chosen above it. See critical fusion frequency.
Lummer-Brodhun photometer A cube in which two adjacent or concentric portions of a comparison viewing screen are separately illuminated by the test source and a standard source. The instrument gives quite accurate readings when the two sources are of identical colour.
Macbeth photometer Photometer using the Lummer-Brodhun cube, an eyepiece and a movable standard source illuminating a diffusing surface seen as an annulus by reflection within the cube. The portion of the source to be measured is seen through the cube as a spot within the annulus. The brightness of the annulus is adjusted until it matches that of the spot.
objective photometer See physical photometer.
physical photometer A photometer employing a radiant energy sensitive element (e.g. a photoelectric cell, a thermopile) and an intensity indicator. Example: Pritchard photometer. Syn. objective photometer.
Pritchard photometer See physical photometer.
SEI exposure photometer; subjective photometer See visual photometer.
visual photometer A photometer in which the equality of brightness of a light source or a surface with a comparison standard source is made by visual observation. Examples: flicker photometer; Lummer-Brodhun photometer; Macbeth photometer; SEI photometer. Syn. subjective photometer.
Millodot: Dictionary of Optometry and Visual Science, 7th edition. © 2009 Butterworth-Heinemann