Improving Lower Beam Visibility Range 2005-01-0441
It is well known that if there is too much light intensity too close to the vehicle, the driver's eye adapts to the high intensity. The driver's ability to see obstacles far away is then decreased. This is why headlamp intensities are limited at 4D. The 1.5D, 2R headlamp test point with no maximum values specified may or may not be located low enough in the pattern to cause this phenomenon with current passenger car headlamp mounting heights.
Discussions with engineers who have been involved in headlamp optical design for many decades (Reference 1) indicates that the original function of the 1.5D, 2R test point was to find the maximum candela (cd) contained within the beam. Searching for the maximum cd with a hand crank goniometer was a difficult and lengthy job. With the filament sizes and focal lengths used in headlamps in the US in past years, the maximum was always found in close proximity to this point. I, too, observed this in the early years of my career. Range effects of differing intensities at this test point were investigated to determine if this test point is still needed for purposes of pedestrian detection.