* 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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Search the history of over billion web pages on the Internet. Full text of ” Macbeth illuminometer. Norman Macbeth, consulting illuminating engineer. This illuminometer differs from all others in that it includes a reference standard against which the illuminometer may be checked at any time.
In making this check, there is no need for a dark room or any auxiliary photometric apparatus. By the use of the reference standard, personal errors are eliminated, for each observer makes his own calibration of the illuminometer. The convenience and compactness of the Macbeth Illuminometer have resulted in its adoption as a part of other photometric instruments.
A recent example of this is the adoption of the Macbeth Illuminometer for use with the Absolute Reflectometer, developed at the U. Bureau of Standards by Mr. The method of its use is also somewhat different, as will be explained later. This test plate is made of a white material of good diffusing qualities.
Care has been used in the selection of this plate to insure, as far as possible, its coefficient of reflection being constant for all angles of incident light. The test plate becomes a secondary source of light, the brightness of which is compared with that of a translucent screen within the instrument which is illuminated to a known intensity by a small Mazda lamp. The scale of the instrument is calibrated in foot-candles, and when standardized it allows for the absorption of the test plate; hence the device is direct reading and the values secured give the intensity of illumination on a given surface.
This value is in terms of “apparent foot-candles” emitted and usually renders the brightness of sources or surfaces direct reading from the same scale on the instrument without the use of factors for multiplying or dividing the scale values excepting where results are desired in terms of candle-power per square inch, square foot, square centimeter or square meter. The scale follows the inverse square law and is theoretically correct and not experimentally determined for each instrument.
A Lummer-Brodhun cube is used, as it is more sensitive than any other type of screen and permits a quicker and more accurate balance. The prisms are so arranged that a circular field, and not the usual elliptical field, is seen when looking through the telescope. All optical parts may be readily removed for cleaning. A direct and simple means is provided for standardizing the Mazda working standard lamp within the instrument.
Thus the user calibrates the instrument for himself, when and where he pleases, and does not depend upon the factory calibration.
It is well known illmuinometer a large personal element enters into the reading illmuinometer a photometer. 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.
Every effort has been made to co-ordinate properly the qualities of compactness, light weight, accuracy, completeness and cost. The battery may weigh from 1H to 4 pounds, depending upon the kind and size of cells used. The three main parts are the Illuminometer, the Controller and the Reference Standard. A Lummer-Brodhun cube is mounted in the rectangular head. By removing the head from the tube and then taking out two screws the cube may be removed for cleaning.
It is quite easily replaced, it being impossible to return it to a wrong position. The photometric field is viewed through the telescope. The aperture opposite the telescope is aimed or pointed toward the test plate, or any surface of which the brightness is to be measured. The lamp carriage is moved up and down in the tube by means of a substantial rack and pinion operating upon a square brass rod to which the carriage is fastened.
This rod is seen projecting from the bottom of the tube Figs. In this connection it is important to note that the control of the travel of the working standard is illuminomwter. All parts involved are metal. An index point is attached to the bottom of the tube. As will be Fig. Cross Section of Illuminometer explained later, ilouminometer index mark is adjustable to allow for variations in filament position of different working standard lamps.
Special attention has been given to the elimination of reflection in the interior of the tube. That this has been successfully done is attested by the fact that the scale follows the inverse square law. The illuminometer weighs 20 ounces. It is supplied with a shoulder strap for convenience of operation and observation when using the instrument.
The controller comprises the battery for operating the lamps, a Weston mil-ammeter, two close regulating rheostats, one for the working standard and one for the reference standard lamp, hereafter called the Reference Standard, and a double-throw switch, by means of which the mil-ammeter may be brought into either the working standard circuit or the reference standard circuit.
All these parts are mounted upon a hard-rubber plate, which is in turn mounted upon a hardwood base. The controller is shown in Fig. Around the edges of the wooden base are six plug connectors; one of these macveth for the attachment of the working standard, a second for the attachment of the reference standard, and the four remaining ones for battery connections.
The equipment is ordinarily operated from two No.
Colour matching filters for Macbeth illuminometer – IOPscience
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 illuminometter been removed, this resistance being just equal to the resistance of the mil-ammeter, thus avoiding a change of current through either lamp. The diagram of connections of the controller is shown in Fig. Diagram of Connections of Controller By using a mil-ammeter illiminometer of a voltmeter for the control of the lamps, there is no liability of error due to changes in contact resistances, the breaking of strands in the flexible cords, and other possible sources of difficulty.
All flexible cord ends are made up with set screw con- nections so that new cords may be substituted without trouble. Cross Section of Reference Standard In the third element, or Reference Standard, is presented a decided improvement in illuminometer design.
It is illustrated in Fig. A cross section is shown in Fig. By the use of the Reference Standard, the illuminometer may be checked at any time or place, doing away with the necessity of a dark room and auxiliary photometric apparatus and with the inconvenience and expense of laboratory standardized working standard lamps. The ease of frequent calibration permits the use of working standard lamps at a very much higher efficiency than ever attempted before, thus securing better color of light and considerably reducing the current demand and consequent battery capacity.
The elimination of the personal factor which is always present when using illuminometers standardized by others is of the greatest importance. In the Macbeth Illuminometer each operator standardizes the illuminometer against liluminometer exact illuminomeer illumination intensity and thus com- pensates for the personal difference of various photometric observers. The Reference Standard consists of a metal housing in which is mounted a standardized lamp, fully protected with diaphragm screens.
The interior parts, after standardization, can be effectively sealed. The lamp used is seasoned and illuminometsr run at such low efficiency and for such short times as to insure the greatest possible constancy. The construction macbdth the Reference Standard is shown in Fig. In using this element it is placed upon the test plate so that the plate is illumknometer by the standardized lamp through the opening C. Before leaving the factory the Reference Standard lamp is so seasoned and calibrated that when a illuminnometer of the value given in the accompanying certificate is passed through the lamp there will be a definite intensity of illumination upon ilkuminometer test plate.
The illuminometer may then be calibrated by placing the sighting aperture into the hole marked D and adjusting the current through the working standard. In the selection of this material a number of points were considered.
The character of the test plate should be such that its coefficient of reflection is as nearly macbegh possible independent of the angle of incidence of the light falling upon it or the position from which it is observed.
Such a surface has never been secured. An important advance, however, has been made beyond previous practice. Test Plate Curves found that the reflecting characteristics of surfaces varied with different materials and also with different surface conditions of the same material.
Curve B represents the results from block magnesium carbonate. Further it is not a practical material to use for test plates. The plates furnished are of glass finished by a special process These plates may, if care is used, be washed with soap and water without any danger macbet changing the character of the surface.
Screens The scale of the illuminometer is from 1 to 25 foot-candles. In order to increase the range of measurement, absorbing screens are provided.
Full text of “Macbeth illuminometer.”
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. Screens of various densities may be used, either neutral or colored, for selective absorption.
These screens are very easily inserted or removed. The total range of the instrument with the two screens ordinarily provided is from about. Showing Horn Attached to llluminometer SCREENS Continued Special screens of low absorption, which may be used together with any of the neutral ab- sorbing screens, are available for use in making measurements of daylight, etc. These screens overcome the difficulty which has always been experienced in making illumination measurements when the color of the light under test differs greatly from that of working standard lamps.
Colour matching filters for Macbeth illuminometer
TRIPOD A light weight, easily adjusted tripod is provided for holding the test plate in any desired position from horizontal to vertical, and at various heights. In passing it may be noted that in this tripod there are no set screws to lose, as all parts are held together by friction clamps. Horn In making brightness measurements on ceilings or other high surfaces it is convenient to use an attachment which provides for holding the illuminometer in a comfortable position while viewing these surfaces.
This attachment consists of a light weight metal elbow or horn with screening diaphragms and a mirror set at an angle of 45 degrees. This horn may be slipped over the illuminometer viewing tube.
When using the horn, a comparison with the Reference Standard must be made with the horn in place to take into account the absorption of light by the mirror. In most illuminometers now on the market the light to be measured is received on a small test plate fastened upon the illuminometer. When measurements are being made at, say, a inch height this necessitates a rather cramped tiring position of the operator when reading the illu- minometer. With the Macbeth Illuminometer as ordinarily used, that is, placing the test plate in the plane where measurements are being made, the operator can stand upright in a normal position when making tests.
If, however, 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. When using the small test plate the standardization should be made with this test plate. 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.
If there are several observations to be made an assistant may carry the con- troller, or it may be set upon a table or other support. If dry cells are to be used, two No. Connect the battery to the leads provided. On the outer ends of these leads are plug connectors.
The one marked — should be connected to the receptacle marked 2. Small, light weight, portable storage cells, such as the Porox, may be substituted if desired.