Adaptive Optical Solutions

Michael Strazzanti, Illume LLC

The fundamental dilemma in forward lighting is the converse relationship between providing sufficient visibility for the driver and limiting the excess glare generated toward oncoming traffic. Research performed at the University of Michigan Transportation Research Institute in Ann Arbor indicates that more than 2300 lives per year could be saved if automotive lighting systems provided perfect nighttime lighting conditions.

Constant use of the high-beam lamp could prevent pedestrians from being hit at night and save thousands of lives annually. However, the glare produced by high beams causes discomfort and disability for oncoming traffic.

Lamp designs that use switching optic elements to provide adaptable beam patterns someday will allow control over light output at specific coordinates ahead of the vehicle and will alleviate the need to sacrifice driver visibility for glare minimization. A single light source and a single reflector system together could fulfill forward-lighting requirements while at the same time providing adaptive glare control.

An adaptive front-lighting system beam pattern is another way of ensuring nighttime driving safety. Current designs use mechanical methods of repositioning the headlight and its components, but a new design features electrically activated lenses and light diffusers that create various beam patterns for the lighting system (Figure 1).

Figure 1. This image depicts a high-beam light with a diffusive light filter affixed to it. By attenuating the light filter, the light output is altered. The images at left show the impact of the filter’s activation on perceived glare. The images to the right show the effect of the filter on the beam pattern produced on a test wall.

Such systems will enable the selection of an infinite number of beam pattern distributions by essentially pixelating the headlight. Current systems require the driver to switch from one beam pattern to another, but the new system will allow the driver to use modified beam patterns. For example, when using high-beams and traffic approaches, the driver must give up the improved visibility of the high beams to prevent glare for the opposing driver. With the new system, he or she will be able to retain a large portion of the high-beam pattern while reducing only that portion of the light beam that produces glare for the opposing driver. Such a system offers a dynamic and adaptive headlight that provides light precisely where it is needed for driver visibility and that reduces unwanted output leading to glare. The system also is nonmechanical, which reduces the complexity and cost of both design and manufacture. The improved function of a single headlight reflector will eliminate the need for secondary and auxiliary lights, thereby reducing overall lighting system costs.

A major drawback to this design involves the transmission variance with operational temperature experienced by liquid crystal films. However, by combining a tunable focal length lens, an optimized reflector design to reduce hot spots on the headlight lens and transparent heating films, the environmental factors can be overcome.

Also under development is a taillight design that includes a single reflector/light source module to provide all rear lighting functions. A combination of light scattering and dichroic dyed liquid crystal films attenuates the brake, turn and backup light (Figure 2). The major benefit to this design is the elimination of multiple taillight reflector housings and bulbs, which reduces system cost. Conventional systems eliminate these segments by using a red brake and turn signal. However, the backup light must be white in the US; in Europe, an amber turn signal is required by law. Using liquid-crystal-based color filters, a single bulb reflector housing can produce all of the rear lighting signal functions in the appropriate colors.

Figure 2. These images show Illume’s taillight prototype in various signal states. A common dual-filament SAE 3157 taillight bulb is used as the light source. The lamp lens is divided into three segments with light-diffusive films and one red dichroic dyed film. The films are each independently connected to an electrical drive circuit. When V ≠ 0 the diffusive films are transmissive and when V = 0 they are diffusive. The red dichroic film is transmissive and colorless when V = 0 and transmissive and red when V ≠ 0. In the image at left, the minor bulb filament is powered, all diffusive films are clear and the dichroic film is red. The images at center and right show the major bulb filament powered with films activated to produce back-up and brake-with-back-up signal states.

Matching the exact color coordinates needed for these signals as dictated by SAE regulations was a major hurdle in their design. A careful mixing of dichroic dye ratios combined with multiple filter layers achieved the necessary color shifts. To create a futuristic look, another application of light scattering and dichroic dyed films can completely conceal the front and rear lights using layers. The main benefit of this approach is the elimination of mechanical systems to raise and lower the headlight for concealment and for aerodynamic purposes. A continuing challenge of this design is achieving film appearance homogeneity across the large area being covered. However, as work continues and new designs emerge, applications in addition to automotive lighting may one day benefit from this technology.

Meet the author

Michael Strazzanti is the owner of Illume LLC of Cleveland; e-mail: mstrazz@illumeco.com.