* I LEEDS & NORTHRUP COMPANY I INTRODUCTION The Macbeth Illuminometer was developed by the Leeds & Northrup Company in con- junction with. Looking for Macbeth illuminometer? Find out information about Macbeth illuminometer. A type of portable visual photometer in which the light to be measured is. The accuracy of the Macbeth illuminometer was studied by measuring a known source. The mean of a number of measurements from a number of operators.
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Any of these publications will be sent upon request. The scale follows the inverse square law and is theoretically correct and not experimentally determined for each instrument. OSA will be closed for the holidays from 21 December On the outer ends of these leads are plug connectors. You do not have subscription access to this journal. This test plate is made of a white material of good diffusing qualities. These screens are made of Wratten filters which may be placed one side or the other of the Lummer-Brodhun cube, thus widely extending the normal range of the instrument.
Further it is not a practical maxbeth to use for test plates.
The illuminometer may then be calibrated by placing the sighting aperture into the hole marked D and adjusting the current through the working standard. Tripod Attachment This is an attachment provided for holding the illuminometer in a horizontal position on the tripod when it is desired to use the instrument for making illumination measurements with the horn and translucent test plate at the inch height. The method of its use is also somewhat different, as will be explained later.
When the mil-ammeter is thrown from one circuit to the other a resistance is auto- matically thrown in the circuit from which the mil-ammeter has been removed, this resistance being just equal to the resistance of the mil-ammeter, thus avoiding a change of current through either lamp.
Table I Percentages of total brightness measurements falling within deviation ranges.
The illuminometer proper macbetn a black tube, 23 cm long and 4. Threshold data taken under calibrating conditions for the Macbeth illuminometer. Percent of measurements made by each operator falling within deviation ranges. One of the accessories within the case is a white test plate, with essentially constant brightness from all angles of observation.
Lumen The lumen is the unit of luminous flux or emanation of light from a source, and is that quantity of light which will produce a normal illumination of one foot-candle over a surface of one square foot. An important advance, however, has been made beyond previous practice.
Figures 7 You do not have subscription access to this journal. The diameter of the field of observation is roughly one-tenth of the distance between the observer and the surface being observed. If dry cells are to be used, two No. It is supplied with a shoulder strap for convenience of operation and observation when using the instrument. This important preventive of carelessness cuts in resistance in the two lamp circuits and prevents passing too much current through the lamps.
If there is a color difference it will be impossible to obtain this disappearance. This “personal equation” is practically eliminated in the Macbeth Illuminometer as every user calibrates his own instrument and does not have to use a calibration which may have been correct for the person who calibrated the instrument in the laboratory, but probably is not correct for him, 4.
If, maxbeth, he should desire to make measurements in the old way, a cap for mounting on the horn and carrying a small translucent test plate is furnished with the equipment. A surface with five foot-candles incident would have an absorption of 20 per cent illuminmeter the emitted light or brightness in a given direction was four “apparent foot -candles. If the surface under obser- vation is of exactly the same color as the light from the working standard the line of demarkation between the two fields will disappear, when a balance is obtained.
Turn the rheostat A in the direction opposite to that indicated by the arrow, until the reading of the mil-ammeter corresponds to the current value on the Reference Standard certificate. This renders the scale direct reading throughout its entire range for the new lamp.
That this has been successfully done is attested by the fact that the scale follows the inverse maacbeth law.
Login or Create Account. The reference lamp should be disconnected as soon as the working standard has been calibrated. If the index mark is not in exact line with the special mark on the scale loosen the screw holding the index plate and move the plate until the two marks coincide.
It is illustrated in Fig. As will be Fig. Test Plate Curves found that the reflecting characteristics of surfaces varied with different materials and also with different surface conditions of the same material.