* 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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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. 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. A surface with five foot-candles incident would have an absorption of 20 per cent if the emitted light or brightness in a given direction was four “apparent foot -candles.

In no case should more than six volts be applied to the controller. Assuming that the illuminometer has been calibrated, place the iilluminometer plate at the point in the plane horizontal or inclined where a measurement is desired.

The elimination of the personal factor which is always present when using illuminometers standardized by others is of the greatest importance. Small, light weight, portable storage cells, such as the Porox, may be substituted if desired. Measure the illumination upon the test plate in the manner previously described.

362 – Macbeth Illuminometer

The character of the test plate should be such that its coefficient of reflection is as nearly as possible independent of the angle of incidence of the light falling upon it or the position maceth which it is observed.


A new current value will be required for the working standard. You do not have subscription access to this journal. Figure files are available to subscribers only. It is important that the Reference Standard be used as little as possible in order that its calibration may be retained over a long period. Use of Absorption screens Fig. An index point is attached to the bottom of maacbeth tube.

If the light source illumlnometer not emit equal amounts of light in all macbeeth the average is obtained and is known as the mean spherical candle-power. For brightness of a high order it is usually stated in candle-power per square inch or per square centimeter, although for reflecting surfaces of a lower order of brightness candle-power per square foot or per square meter has been found to result in more appreciable values.

Macbeth illuminometer | Article about Macbeth illuminometer by The Free Dictionary

The construction of the Reference Standard is shown in Fig. At 30 feet the diameter of the field is 3 feet. By continuing to use this site, you agree to our use of cookies. When using the small test plate the standardization should be made with this test plate.

Colour matching filters for Macbeth illuminometer – IOPscience

All parts involved are metal. This illuminometer differs from all others in that it includes a reference standard against which the illuminometer illuminomdter be checked at any time.

Enoch, and William R. Connect the battery to the leads provided. Equations displayed with MathJax. OSA will be closed for the holidays from 21 December In order to increase the range of measurement, absorbing screens are provided. A Illuminomeger cube is mounted in the rectangular head. 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.

Macbeth illuminometer

Click here to see what’s new. On iluminometer outer ends macbetb these leads are plug connectors. Please login to set citation alerts. This test plate is made of a white material of good diffusing qualities. 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. Such a surface has never been secured.


The lamp used is seasoned and is run at such low efficiency and for such short times as to insure the greatest possible constancy.

Percentages of total brightness measurements falling within deviation ranges. All optical parts may be readily removed for cleaning.

In actual use the working standard current is to be kept at the value determined by this check test. Morris, and Forrest L.

Apparent Foot-candle The brightness in “apparent foot -candles” emitted from a source or surface, if distributing light uniformly in all directions, as from a hemispherical source or from a perfectly mat surface, when divided by illuminlmeter 3. One of the accessories within the case is a white test plate, with essentially constant brightness from all angles of observation. 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 kacbeth not correct for him, 4.

Cross Section of Reference Standard In the third element, or Reference Standard, is presented a decided improvement in illuminometer design.

Around the edges of the wooden base are six plug connectors; one of these is for the attachment of the working standard, a second for the attachment of the reference standard, and the four remaining ones for battery connections.