The widespread use of flat panel displays (FPDs) in televisions, computer monitors, automotive displays and in portable products has created the need for accurate, fast and cost-effective methods for measuring colour and luminance, uniformity, contrast ratio, view angle and for detecting display defects.
Luminance & Colour Measurements
The Konica Minolta LS-100 and LS-110 are simple, affordable, hand-held photometers that provide for spot luminance (brightness) measurements. The Konica Minolta CS-100A is the colorimeter version of the LS-100. The Konica Minolta CA-210 is a benchtop, tristimulus spot colorimeter that is used principally for the measurement of white balance, white uniformity, luminance, chromaticity, flicker and gamma of various flat panel display devices including LCD. The accuracy of filter photometers is always reduced when measuring narrow spectrum light sources such as LCDs and 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 measure 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 display at once, localised luminance and colour differences (defects) can be easily detected automatically – artefacts that spot meters might miss.
A number of application-specific, "bolt-on" software applications have been developed for the ProMetric imaging photometers for those working with displays.
View Angle Measurements
There are two generic approaches to measuring the view angle performance of a display - the variation of luminance with direction of view. The first is to measure the view angle performance for the whole display, one angle at a time. The other is to measure the complete hemispheric view angle performance for one spot on the display at a time.
Radiant Imaging have developed state-of-the-art solutions for both measurement approaches. Full screen view angle measurements are performed by the PM-FPMS near-field goniophotometer. PM-FPMS provides fully automated measurements of brightness and colour uniformity as a function of viewing angle for all FPD technologies and display back lights. Because the PM-FPMS system captures a full image of the display or component at each measurement angle, it provides much more comprehensive information than can be obtained from traditional spotmeter-based measurements.
Instantaneous hemispheric view angle measurements for one spot on the display at a time are performed by Radiant's IS-VA Imaging Sphere. The Imaging Sphere is an innovative, ultra-fast goniophotometer based upon a ProMetric imaging photometer for instananeous angular analysis of displays. With the Imaging Sphere, you measure the light distribution for all angles instantaneously. Compared with traditional conoscopic techniques, the Imaging Sphere is much less expensive and can record measurement spots of up to 40mm diameter at up to 85° elevation. Conoscopic measurements are rendered inaccurate when their small measurement spot approaches the typical LCD pixel size.
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