The color and luminance distributions of large light sources are difficult to measure because of the size of the source and
the physical space required for the measurement. We describe a method for the measurement of large light sources in a
limited space that efficiently overcomes the physical limitations of traditional far-field measurement techniques. This
method uses a calibrated, high dynamic range imaging colorimeter and a goniometric system to move the light source
through an automated measurement sequence in the imaging colorimeter's field-of-view. The measurement is performed
from within the near-field of the light source, enabling a compact measurement set-up. This method generates a detailed
near-field color and luminance distribution model that can be directly converted to ray sets for optical design and that
can be extrapolated to far-field distributions for illumination design. The measurements obtained show excellent
correlation to traditional imaging colorimeter and photogoniometer measurement methods. The near-field goniometer
approach that we describe is broadly applicable to general lighting systems, can be deployed in a compact laboratory
space, and provides full near-field data for optical design and simulation.
Human vision and perception are the ultimate determinants of display quality, however human judgment is variable,
making it difficult to define and apply quantitatively in research or production environments. However, traditional
methods for automated defect detection do not relate directly to human perception - which is especially an issue in
identifying just noticeable differences. Accurately correlating human perceptions of defects with the information that can
be gathered using imaging colorimeters offers an opportunity for objective and repeatable detection and quantification of
such defects. By applying algorithms for just noticeable differences (JND) image analysis, a means of automated,
repeatable, display analysis directly correlated with human perception can be realized. The implementation of this
technique and typical results are presented. Initial application of the JND analysis provides quantitative information that
allows a quantitative grading of display image quality for FPDs and projection displays, supplementing other defect
detection techniques.
Light emitting diodes (LEDs) are being utilized as the light source in increasingly complex and sophisticated products,
including flat panel displays, surgical lamps and even digital projectors. These applications place extreme demands on
LED performance, which, for both the developer and manufacturer, translate into the need to precisely characterize and
control source output, specifically color and luminous intensity distribution characteristics. Unfortunately, the
traditional methods for performing luminous intensity and colorimetric measurements of LEDs suffer from several
significant drawbacks. In particular, spot photometers and radiometers only sample a very limited amount of source
output and operate very slowly. The latter factor can be an important consideration, even in research settings, because
LED output is often not stable over time, especially during warm-up or in the presence of temperature or input power
fluctuations. Thus, a long data acquisition period can make an instrument report spatial output variations that don't
really exist. Now, new instrumentation based on the Imaging Sphere enables rapid, high spatial resolution measurement
of LED color and luminous intensity over an entire hemisphere. This paper reviews the parameters typically utilized to
characterize LEDs, explores Imaging Sphere operation, and compares the results of Imaging Sphere measurements with
highly accurate reference data from a goniophotometer.
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