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.