Clearly Visible Presentations, LLC
July 13-15, 2021 Optics, Lighting and Visibility for the Forensic Investigator
West Chester, OH
(Contact us at ClearlyVisPres@aol.com or Steve Ashton (513-240-4887)
I have an erstwhile studio at my home office from which I have conducted on-line classes. To date, those have been one-on-one classes although I have the resources to teach more, perhaps up to 100 people using my Glance service.
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How to Compute Veiling Glare
It was 6:40 a.m. on July 30, 2010 on a country road in southwest Ohio. A young man was in a 2002 Ford Mustang heading to work. Sky conditions were dark with the sun still 10 degrees below the horizon. As he came around a corner and headed down a hill, there was a vehicle ahead of him. It seemed to be going slow and then he realized that it was stopped across from a house on the right. He slowed down and eased to the right to go past. But, just as he passed by, there was a flash of light directly ahead of him and he struck something. On stopping, he realized that it was a person. That person had been standing right alongside the stopped Ford Bronco. We recreated the scene with the actual vehicles. Can you see the person standing outside the car next to the driver's side?
200 ft 100 ft
The individual was lost in the glare of the Bronco’s headlights. How do you go about calculating the glare influence? All the components are available: headlamp intensity pattern from both vehicles, road profile, age of the Mustang driver, location of the pedestrian and reflectance of the pedestrian’s clothing. By carefully analyzing the headlamp intensity maps for both vehicles, it is possible to calculate the luminance (brightness) of the glare field that surrounds each headlamp and compare it to the luminance of the pedestrian’s clothing within the illumination field cast by the Mustang’s headlamps.
The General Disability Glare Equation published by the Congress Internationale de l’ Élairage (CIE) can be used to determine that veiling luminance as a function of angle from the glare source(s) to the gaze point. That equation takes the form:
where Lv is the veiling glare, Θ is the angle from gaze point to glare source, Age is the viewer’s age in years and p is the viewer’s eye pigmentation (running from 0 to dark and 1.2 to very light).
To determine the luminance of the pedestrian’s clothing, identify the rays from the striking car’s headlamps that strike the clothing and determine their intensities. Determine where those rays strike the pedestrian’s clothing and thence the reflectance of the clothing at those points. From those values, the luminance of the areas under analysis can be determined by:
Compare the total luminance of the pedestrian to the total luminance of the glare fields to determine if pedestrian luminance is high enough to see through the glare fields.
To learn more, download this paper: