Pro Lite Technology

Automotive Applications

BMW 5-Series Xenon Headlight

Light measurement plays an important role in the development of automobiles, from the colour and brightness of interior and exterior lighting, to the beam pattern of headlamps and the brightness and colour of instrument clusters and displays.

Exterior Lighting

Traditionally, the illumination performance of vehicle exterior lighting and headlamps has been determined using a far-field goniophotometer. This type of instrument places the lamp on a motorised stage that rotates and tilts the headlamp with respect to a photometer that views the lamp along a fixed direction of view. Goniometric measurements are normally performed in a dark room at a distance of 25m for headlamps and 3.162m for other lamps. The photometer records the illuminance from the headlamp one angle at a time. Optronik's far-field goniophotometers are the instruments of choice for testing vehicle exterior lighting. A family of five goniometer frames can handle any size or weight of lamp which ensures that even the very largest lighting assemblies can be tested. All axes of motion are motorised and control software includes algorithms which fully automate the various ECE and SAE statutory test sequences.

An alternative approach for in-house product development testing is an imaging photometer. Radiant Imaging's ProMetric imaging photometer is a powerful, CCD-based light and colour measurement instrument that provides for increased productivity compared with traditional goniometric measurements. Whereas a goniophotometer measures the illuminance and colour from a headlamp 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 miss. In addition, the capital cost of an imaging photometer is much less than that required for a typical motorised goniophotometer.

Radiant Imaging developed PM-HL Test software to further simplify the measurement of automotive headlamp beam patterns with its ProMetric imaging photometers. The software automatically determines the “beam elbow” in the illumination pattern, aligns the camera image to this position, measures the illuminance at the ECE R20 specified test points for left or right hand drive and provides for simplified pass/fail type reporting of the device under test.

LEDs are starting to be used as DRLs (daylight running lights). To achieve a consistent colour and quality appearance, manufacturers may wish to test the colour temperature of these high brightness white LEDs. Testing the colour temperature of LED DRLs is easily performed at moderate cost and with high colorimetric accuracy using an Ocean Optics spectrometer configured for spectral irradiance measurements.

Retro-reflectors are used as safety devices to enhance the visibility of objects under low light conditions. A retro-reflector is designed to return the rays of light in the direction from which they came regardless of the angle of incidence. Retro-reflection is used on road surfaces, road signs, vehicles and clothing. When the headlights of a car illuminate a retro-reflective surface, the reflected light is directed towards the car and its driver, and not wasted by going in all directions as with a diffuse reflection. The Optronik RMM-10 is a high-speed "reflex checker" designed for production-line testing of retro-reflective materials, specifically automotive reflectors and road markings. It is commonly used in the process control of plastic moulding machines.

Instrument Panels & Displays

LEDs are used extensively for display backlighting, for subtle mood lighting in cars’ cabins and for illuminating switches and panel indicators. It is vital that the LEDs selected provide consistent illumination, create the required level of brightness (luminance) and emit exactly the desired colour. Visual comparison of LEDs is extremely subjective (and of questionable safety if the LEDs are very bright) and simply cannot be relied upon to quantify the performance of the light source or display. The solution is a luminance photometer or colorimeter.

Spot luminance meters such as the Konica Minolta LS-100 and LS-110 are simple, affordable, hand-held photometers that provide for spot luminance measurements down to 4.8mm diameter (or 0.4mm with an optional close-up lens). The Konica Minolta CS-100A is the colorimeter version of the LS-100 with a minimum measurement spot size of 14.4mm (or 1.3mm with close-up lens).

The accuracy of filter photometers is always reduced when measuring narrow spectrum light sources such as LEDs. The Konica Minolta CS-200 is a hybrid "spectral colorimeter" that combines the ease-of-use and relative affordability of the CS-100A with a colorimetric accuracy approaching that of the research-grade Konica Minolta CS-2000 spectroradiometer.

As the name suggests, "spot” photometers measures the brightness and colour of an LED or display one spot at a time. At most, you can select from up to five measurement spot sizes, either by fitting close-up lenses or by selecting alternate measurement apertures in the photometer. If a more flexible and productive (albeit more costly) solution is more your thing, you should consider an an imaging photometer, specifically a ProMetric CCD imaging photometer made by Radiant Imaging.

ProMetric imaging photometers are powerful, CCD-based spatial light and colour measurement instruments that provide for increased productivity compared with traditional spot photometers and colorimeters. Whereas a spot photometer can only measure the brightness and colour of one point on a display or light source at a time, a CCD-based ProMetric photometer can measure literally millions of points simultaneously. The measurement spot size can be selected in software after the measurement has been made, and moreover, any number of analysis points can be defined - and recalled - as required. In addition, because the ProMetric camera views the whole light source or display at once, localised luminance and colour differences can be easily detected – artefacts that spot meters might miss.

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