Pro Lite Technology

Automotive Headlamp Testing

Light: the fuel of life

Imaging photometers rapidly tests beam illumination patterns

Ring Automotive Ltd (Leeds, UK) is a market leader in the automotive lighting sector. A key market for the company is the supply of performance bulb upgrades as replacements for the original equipment (OE) lamps fitted to car headlights. The company needed a way of comparing the illuminance, chromaticity and colour temperature of their aftermarket bulbs and competitor products against OE lamps in order to establish their performance benefits. In addition, Ring needed a means of qualifying its lighting products and of assessing the performance of their lamps against the requirements specified in the applicable UN ECE R20 vehicle lighting regulations.
 
Traditionally, the illumination performance of a headlamp has been determined using a goniophotometer. This type of instrument places the headlamp on a motorised stage that rotates and tilts the headlamp with respect to a photometer that views the headlamp along a fixed direction of view. Goniometric headlamp measurements are normally performed in a dark room at a distance of 25m. The photometer records the illuminance from the headlamp one angle at a time. Goniometric measurements of this type achieve high accuracy but have a high capital cost associated with them, generally limiting their use to national standards testing and type-approval laboratories. The relatively slow speed of measurement of a traditional goniophotometer also renders comparative testing of light sources to be time consuming and limited in scope.
 
Peter Harding, Ring’s Commercial Director, recognised that he needed to invest in a photometric system to support their business development efforts in the lighting market. However, the capital investment associated with a traditional goniometer, the need for a large dark room and other technical limitations were obvious deterrents. Peter, keen to explore all options, approached Pro-Lite. We proposed an “imaging photometer” which is a powerful, CCD-based light and colour measurement instrument that provides for vastly increased productivity compared with traditional goniometric and “spot” measurements of lamps. Whereas a goniophotometer can only measure the illuminance and colour from the lamp one direction at a time, a CCD-based imaging photometer can measure millions of angles simultaneously. Moreover, because the imaging photometer views the whole illumination pattern at once, localised illuminance and colour differences can be easily detected – artefacts that goniometric measurements performed at defined angles might easily miss. In addition, the capital cost of an imaging photometer is much less than that required for even the most basic motorised goniophotometer. The case in favour of an imaging photometer was quickly established.
 
Ring selected a CCD imaging photometer from Pro-Lite. This camera had a high photometric sensitivity and spectral response which accurately matched to the CIE tristimulus observer functions. This provided the necessary level of illuminance sensitivity, spatial resolution and spectral match to the human visual response.  It also came complete with powerful application software that simplified and automated routine tasks such as setting exposure times, performing calibrations and reporting the illuminance, chromaticity and colour temperature of user-defined points-of-interest.  Its powerful, built-in analysis tools include illuminance and colour analysis, simplified pass/fail reporting and multiple graphing and report capabilities.
 
Of importance to Ring was the ability of the chosen measurement system to analyse the illuminance pattern from a headlight in accordance with the muliti-point test pattern specified in ECE regulation R20.  The information necessary to perform this analysis manually was already contained within the standard camera software.  However, to further standardise the testing of Ring's lamps and enhance accuracy, consistency and productivity, Pro-Lite supplied an additional software application for the camera that would automatically determine the datum position ("beam elbow") in the illumination pattern, align the camera image to this position, measure the illuminance at the ECE R20 specified test points for left or right hand drive and provide for simplified pass/fail type reporting of the device under test.
 
This case study formed the basis of an article published on optics.org. Pro-Lite gratefully acknowledges the permision of Ring Automotive to publish this article and for permission to use the image shown above. For further information on imaging photometers, click here.
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