Abstract
A modeling procedure was proposed for the through-hole LEDs commonly used in traffic signs. The measurements from a sample batch of LEDs were performed at several midfield distances to provide a set of representative angular intensity distributions as the target pattern in the modeling process. The flat outer dimensions of the LED were accurately measured while the curvature and refractive index of the packaging dome were roughly estimated. These physical parameters were used to build a preliminary LED model in the Monte Carlo simulation software. The simulated angular intensity distribution at each distance was generated by tracing 20,000,000 rays. The normalized cross correlation (NCC) between the measured and simulated data was calculated to represent the resemblance of the model to the real LED. The roughly estimated parameters were then varied within their physical limits to optimize the NCC value. The possibilities of two parameters having interactions were also considered. The final model has all NCCs above 98.8% between the target and simulated patterns.
Highlights
IntroductionOften overlooked in the application phase is that LEDs are more probable to induce glare that affects the legibility and visual comfort of traffic signs, which are the primary purposes of traffic signs
With the popularity of LEDs growing around the world, they are gradually replacing the lighting in both indoor and outdoor applications, including various types of traffic signboards.Often overlooked in the application phase is that LEDs are more probable to induce glare that affects the legibility and visual comfort of traffic signs, which are the primary purposes of traffic signs
Some research done on LED billboards [1], which are similar to freeway traffic signboards, has shown that the high luminance of billboards can cause discomfort
Summary
Often overlooked in the application phase is that LEDs are more probable to induce glare that affects the legibility and visual comfort of traffic signs, which are the primary purposes of traffic signs. This is mainly due to some of the characteristics of LEDs, such as having a small die size or light emitting area and high directivity. Some research done on LED billboards [1], which are similar to freeway traffic signboards, has shown that the high luminance of billboards can cause discomfort. Size, and font of the characters on the signage influence legibility [4,5,6]
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