Type of Photometers

Type of Photometers Points : Type of Photometers, Bunsen Grease Spot Photometer, Flicker Photometers, Photometry, Photometer Bench 1. Bunsen Grease Spot Photometer There are two types of Lummer Brodhun heads — one is the equality of brightness type and second is the contrast type. The contrast type is more accurate and, therefore, more used in photometric measurements. The Lummer Brodhun heads can be employed br the measurement of brightness of window with some modifications. 2. Flicker Photometers These photometers are employed when the two sources giving light of different colours to be compared. 3. Photometry We shall now discuss the comparison arid measurement of candle powers. The candle power of a source in any given direction is measured by the comparison with a standard or substandard source employing photometer bench and some form of photometer. The experiment is performed in dark room with dead black walls and ceiling in order to eliminate errors due to reflected light. 4. Photometer Bench The photometer bench consists essentially of two steel rods which carry the stands or saddles for holding the two sources, the carriage for the photometer head and for any other apparatus employed in making measurements. One of the bar carries a bar strip graduated in centimetres and milli-meters. The carriage which slide upon the bench have, except that carrying the photometer head, a circular table which can be rotated in a horizontal plane and clamped in any position. The circular table is provided with a scale graduated in degrees round its edge so that the angle of rotation of lamp from the direction of the axis of bench can be measure. The bench should be rigid so that the source being compared may be free from vibrations and the carriage holding the photometer head should be capable of moving smoothly with every little effort. The photometer head should act as a screen for comparison of illumination of the standard source and the source under test. There are different types of photometers, which can be used for the purpose. Some of them will be described here.