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ABSTRACT:
Light-emitting diode (LED) technology is becoming the choice for many lighting applications that require
monochromatic light. However, one potential problem with LED-based lighting systems is uneven luminance patterns.
Having a uniform luminance distribution is more important in some applications. One example where LEDs are
becoming a viable alternative and luminance uniformity is an important criterion is backlighted monochromatic
signage. The question is how much uniformity is required for these applications. Presently, there is no accepted metric
that quantifies luminance uniformity. A recent publication proposed a method based on digital image analysis to
quantify beam quality of reflectorized halogen lamps. To be able to employ such a technique to analyze colored beams
generated by LED systems, it is necessary to have contrast sensitivity functions (CSFs) for monochromatic light
produced by LEDs. Several factors including the luminance, visual field size, and spectral power distribution of the
light affect the CSFs. Although CSFs exist for a variety of light sources at visual fields ranging from 2 degrees to 20
degrees, CSFs do not exist for red, green, and blue light produced by high-brightness LEDs at 2-degree and 10-degree
visual fields and at luminances typical for backlighted signage. Therefore, the goal of the study was to develop a family
of CSFs for 2-degree and 10-degree visual fields illuminated by narrow-band LEDs at typical luminances seen in
backlighted signs. The details of the experiment and the results are presented in this manuscript.
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