MEASURING INTENSITIES OF ILLUMINATION OVER A LIGHT BEAM

Abstract: A method of and means for measuring intensities of illumination over a light beam using a photometer (8) to measure light intensities of areas across the beam in which the light source (1) is at a defined distance from the photometer (8) and has mechanism to sweep the light source (1) across the photometer (8) progressively or incrementally at different angles of elevation or depression or by using an array of stacked photometers to record a series of points or graphs of the scan.

Description: MEASURING INTENSITIES OF ILLUMINATION OVER A LIGHT BEAM This invention relates to a method of and means for measuring the light intensity of a beam over a defined area and to plot light intensity at individual locations over the defined area, and in particular 5. it relates to the measurement of light intensities issuing from beam light sources with defined boundaries and graded intensities. The customary method of measuring the light intensities from beam sources is to fix the light 10 * . source which projects the beam, and to use a photometer at a considerable number of selected positions in the beam and to plot the points so obtained to give a graph of the intensities across the area at selected positions. Such methods are used, for instance, 15. in high power light sources having relatively wide extension in relation to height, such as is shown in the Specification of Australian Letters Patent No. 485,614, but the methods are not limited to such shaped beams. 20. The above defined method is both time-consuming and lacks the required accuracy because each time a measurement is taken at a different spot in the beam, the photometer has to be set up to the required accuracy, both in relation to angle and distance 25. and position and as it is necessary to have a number of readings the task becomes a time consuming one. The object of the present invention is to provide an improved method and means to measure the light intensity of lamp heads or the like particularly 30. shaped-beam heads and this is achieved by mounting the light source on a platform whereby the angle of the light source can be varied to traverse a selected plane preferably the plane of greatest width in a shaped beam, but can be caused to nod 5. or move otherwise to obtain readings over the required cross-sectional area of the beam, and to use a photometer fixed in relation to the light source and in a position where the light source can be scanned by moving the beam across the photometer to cause the photometer 10. to give reading of luminous intensity along -the scan, or at points along the scan, including scans on each side of the main scan, and then tabulating the results and if necessary applying correction factors for distance variations and the like. 15. Using the prior art methods an analysis could take, conservatively, three hours because of the need to accurately set up the photometer many times during an assessment. As the present invention envisages, in a simple 20. form, a single stationary photometer with the lamp head mounted on a platform arranged to be moved smoothly about a defined axis, the beam is effectively scanned by the photometer, the sequence preferably being carried out at a number of elevation and depression 25 # angles until the required beam coverage is achieved. The elevation and depression angles can be selected manually, but it is possible to have driving means to control the scan about a main axis with further scans on each side effected by power means 30. nodding the platform. The results of these scans are compared by an X-Y plotter, and it has been found in practice that the time for taking a complete reading is measured in minutes as against the relatively long time previously required, and a single scan can for instance be completed in a matter of 8 or 9 seconds for an average 5. area. The advantage of having a fixed photometer at a selected distance from a platform movable about a defined axis hardly needs stressing, resulting in the ability to scan as opposed to spot measurements, 10. with resulting greater accuracy and much higher speed. • - According to one form of the invention, the actual device for carrying out the invention can comprise a platform on which the light source is 15. mounted, which platform is arranged to move about an X axis but the platform is so arranged in relation to the X axis that it can also be moved about a Y axis normal thereto so that when it is required to scan an area the light source can be moved about 20. the X axis, which for instance can give a horizontal scan, and as the light source is directed to traverse the photometer a graph can be drawn showing directly the light intensity over a segment of selected width along the scan line. 25. The next scan can be effected by manually or mechanically moving the platform about the Y axis to a second position and a further scan completed about the X axis to draw another graph of a further segment and so on according to the number of segments 30. required to be measured. According to another form a single sweep is used over an array of photometers stacked normal to the plane of the sweep. The platform support can carry at least one stepper motor or the like to effect the required traverse, and means are provided to correlate the movement of the platform with the light intensity readings 5. given by the photometer, but it will be realised that if point measurements are required switching means could be provided to cause the light source to move to give a point to point reading over the required area. A continuous plot over the area 10. is however generally more effective in that it gives more detail. Thus the device can comprise what we term a ' . , scanning unit which embodies the platform mounted to move about a pair of axes, normal the one to ■ _ι- the other, and provided with means to adjust the position about these axes, control of the movement being from a programmed source provided with the necessary indicator means, the scanning unit being coupled to an X-Y recorder arranged to be in step 20. with the movement of the platform, the X-Y recorder having the signal from a photometer applied to it through a conventional preamplifier. The device can be used for calibrating or recording light intensities over individual areas of the beam 25. and the invention can be applied for instance to the plotting of light intensities over incremental spot areas of the beam of vehicle light assemblies, signal lights for road or railway use, floodlight illumination, laboratory illumination and in fact 30. anywhere an accurate light beam is required, particularly here this needs to have sharp cut-off points or different intensities over certain parts of the field of the beam, the invention allowing ready testing of manufactured light sources for the effective- - JRE OMP WA ness of spread and intensity of light in relation to requirements. To enable the invention to be fully understood, embodiments thereof will now be described with reference 5. to the accompanying drawings in which FIG. 1 is a schematic plan showing a typical arrangement, FIG. 2 is a side elevation of same showing at A a first scan and showing in dotted lines a 10. second scan B, FIG. 3 is a similar side elevation of a modified ' * form of the device, and FIG. 4 is an isometric view of the lamp head platform showing the scanning axis X and the nodding 15. selector axis Y for different elevation and depression angles. The apparatus comprises a support for the lamp 1 shown in FIG. 4 of the drawings, which comprises a base 2 to which is fixed a motor member 3 to move 20. the lamp 1 about the axis X, the shaft 4 of the motor member rotating the carrier 5 which has on it motor means 6 to move a support 7, on which the lamp head 1 is fixed, about a Y axis, so that by rotating the carrier 5 a sweep can be made across 25. the photometer 8 which has a diffuser 9 to thereby record the intensity in the plane shown in FIG. 1 but to give a reading at elevation and depression angles about the Y axis. The motor means 6 are used either as nodding means for the lamp head or for traversing 30. at different elevation or depression angles. The scanning angle is shown at 10. A photometer preamplifier 11 feeds the output signal to the X-Y recorder 12 which is correlated to the scanning unit drive 13. A regulated power supply 14 acting through 5. a remote cable 15 supplies current to the lamp 1, an amp meter 16 and volt meter 17 being used to control operating conditions. In the form shown in FIG. 3 an array of photometer 8A-8E is shown to give readings simultaneously at 10. different elevation angles, and in that form the movement about a Y axis is not required and the lamp head 1 can be mounted directly on the carrier 5 to effect a sweep about the X axis. As in the form shown in FIG. 3 each photometer 15. requires a separate photometer amplifier and recorder channel, the form shown in FIGS. 1 and 2 is preferred as the motor means 6 can step the lamp head to produce :* any required number of stepped sweeps. From the foregoing it will be realised that 20. a simple and effective form of testing device and method of testing is provided in which instead of a photometer having to be successively positioned at a multiplicity of locations, a single photometer can be positioned in a highly accurate manner in 25. relation to a platform which controls the movement of the light source to cause its beam to traverse the photometer according to a particular required pattern, a nodding arrangement on the platform allowing duplication of the scan at spaced localities. 30. Modifications within the spirit of the invention will be appreciated and the invention described need not necessarily be limited to the embodiments described as the principle of a fixed photometer zone, and a light beam scanned across it, forms the basis of this invention, the device as described 5. comprising a platform to support the lamp or light source, which platform is mounted to move about at least one axis and directed to scan the light beam across a fixed photometer zone connected to at least one plotter arranged to act synchronously 10. . with movement of the platform.

Claims: 8 . THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS: 1. The method of measuring intensities of illumina¬ tion over a light beam using a photometer to measure the light intensity of areas across the light beam, characterised by mounting the light source at a defined 5. distance from the said photometer, sweeping the said light source across the said photometer, and progressively or incrementally, recording the light intensities received at the photometer as the light beam scans across the said photometer. 2. The method of Claim 1 characterised by the steps * • , of rotating the said light source about an X axis to sweep the said light source across the said photometer at one elevation and repeating sweeps across the said photometer 5. at different elevations or depressions by moving the said light source about a Y axis normal to the said X axis. 3. The method of Claim 1 characterised by sweeping the said light beam across a stack of photometers, and recording the light reading of each said photometer independently. 4. A device for measuring intensities of illumination over a light beam using a photometer at a fixed distance and position from the light source to measure the light intensity of areas across the light beam, characterised by 5. a platform to support the said light source and means to rotate the said platform about at least one axis to cause points of the light beam to be progressively or incrementally presented to the said photometer during a sweep, a recorder to record the said signal of the said 10. photometer, and means to synchronise the said recorder with the movement of the said platform. 5. A device according to Claim 4 characterised in that the said platform is movable about X and Y axes, driving means to rotate said platform through a segment of a circle about the said X axis, and 5. adjusting means to move the said platform about the said Y axis to record sweeps at different elevations■ 6. A device according to Claim 5 characterised in that the adjusting means about the said Y axis moves the said platform incrementally between sweeps about the said X axis. 7. A device according to Claim 4 characterised by a series of photometers stacked normal to the sweep direction whereby at each sweep a series of areas of the light beam at different elevations 5. are recorded. 8. A device according to Claim 5 characterised in that the said platform comprises a carrier rotatable ■; by motor means about an X axis to cause the said points of the light beam to be presented to the 5. said meter during a sweep, and on the said carrier a support for the said lamp head movable by motor means about a Y axis, a scanning unit to control both said motor means and record said control signal in an X-Y recorder, and a photometer preamplifier 10. to feed the photometer signal to the said X-Y recorder, whereby to record a series of light intensity points over the said light beam at zero angle and different areas of depression and elevation.

Inventors: HIMSWORTH ALAN JAMES, HIMSWORTH, ALAN, JAMES
Applicants: COMMW OF AUSTRALIA, THE COMMONWEALTH OF AUSTRALIA CARE OF THE SECRETAR
Application year: 1982
Main classification: G01J1
IPC codes: G01J1