COLOR could be used in automotive lighting to improve perception of illuminated lights under adverse driving circumstances. Consider what illuminated red colored light means when you're driving your car. If the red light is on a traffic signal light at an intersection you are approaching, you get ready to stop your car, because that is certainly what you will have to do if the light is still red when you reach the intersection. It is an absolute no brainer: when a red traffic signal light is illuminated for the roadway you are driving on, you stop.
Unfortunately, the meaning of illuminated red colored light on the rear of any vehicles ahead of you is much less clear. Do you need to stop, or at least get ready to stop? Maybe yes, maybe no. If you actually do see the red colored light on the vehicle directly in front of you get brighter, yes, you have to at least prepare to stop your own car. But sometimes in real-world driving, you don't actually get to see the red colored lights on the vehicle directly in front of you get brighter. So, at least for a moment, when you see red colored rear lights on the vehicle directly ahead of you, you're not sure whether you must get ready to stop or not. If the red colored lights on the vehicle in front of you are just tail lights, and that vehicle is just driving forward, you probably won't need to stop your own car.
But if the red colored lights on the vehicle in front of you are actually brake signal lights, then you do need to at least prepare to stop. Recognizing the occassional ambiguity of the brake signal lights, several years ago government officials added the high-mounted center brake signal light to supposedly provide an unambiguous signal of braking. But in real-world driving, you see a large number of vehicles in which the high-mounted, center light fails to be illuminated even when the vehicle is being braked. Uh, oh! That can be really bad, because if you see a high-mounted, center light that's not on, it gives you a signal that the vehicle in front of you is not being braked! If the high-mounted center light should be on but isn't because of an electrical failure, the signal of non-braking given by the non-illuminated high-mounted center light could be a contributing cause in some rear-end collisions.
Even in 2018, the need for a strong, unambiguous signal that a vehicle is being braked remains unresolved. The high-mounted center lights gives at best a partial solution. At its worst, when the high mounted center light malfunctions, it can give a signal of non-braking even when the brake pedal of a vehicle is depressed. A far better approach toward optimizing the perceptibility of the red colored brake signal lights, referred to as the RLMS approach, was recommended to the NHTSA (for "National Highway Traffic Safety Administration") in 1995. In RLMS rear lighting, red colored light, and ONLY red colored light, is displayed at the rear of an automotive vehicle whenever the brake pedal of the vehicle is depressed. At all other times, such as when the vehicle is being driven forward at night, all light displayed on the rear of the vehicle is amber rather than red in color. The amber colored (or red colored light during braking) rear light on the side of an intended turn flashes. All specific signals of braking in existing rear lighting systems, i.e., increased brightness of red colored lights and illumination of a high-mounted center light upon braking, are retained. This makes display of red colored light per se a specific signal that the brake pedal of the vehicle ahead is depressed. If you are driving behind a vehicle with RLMS rear lighting, whenever you see red colored light, you know immediately that you must at least prepare to stop your own car. Vehicles with amber colored rear turn signal lights could be converted to color-specific function by a simple addition of a couple of new switches to the electric wiring. Amber colored rear lights would have to be added to existing vehicles with no amber colored rear lights.
The NHTSA had an excellent opportunity in 1995 to do the responsible thing. This would have been to arrange for well planned, comprehensive testing of the RLMS approach, to especially include testing under adverse circumstances. Instead, the NHTSA chose the irresponsible course of action. They chose to do nothing. They dismissed the RLMS approach with the comment "The opinion of the NHTSA ... is that the color of light is a matter of no importance." This might be an accurate observation under ideal circumstances, when the red colored rear lights ahead can be clearly seen to get brighter. BUT it is probably not an accurate statement for the adverse moments in driving, when the intensity increase in the red colored rear lights cannot be seen. Doing nothing in 1995 was the easy thing to do. To do nothing is always the easiest thing to do. But it was not the wise or highly responsible thing to do. Most people accept the idea that "With great power, comes great responsibility." Because it exercises absolute power over automotive matters, the NHTSA also has a very high level of responsibility to the American public. In my opinion, the NHTSA has totally failed to meet its responsibility with regard to a reasonable consideration of RLMS rear lighting. The NHTSA's opinion that light color is not significant in perception of the brake signal may be correct under ideal circumstances, but it is probably not correct under adverse circumstances, frequently encounterred in real-world driving, when the increased brightness of red colored rear lights cannot be seen. ALL favorable features of existing rear lighting systems(increasing brightness when the brake pedal is depressed, the color red for the brake signal lights, and illumination of the high mounted center light) are retained in the RLMS approach. Color specificity is added as an immediately perceptible factor to make the signal of braking truly unambiguous.
How could the NHTSA simply ignore RLMS rear lighting? How can the NHTSA recognize the value of color in the case of the stop sign, but ignore the value of color in a more general sense? How could the NHTSA not utilize its existing resources to confirm OR perhaps disprove the value of the RLMS approach during adverse moments in real world driving?. Testing of the RLMS approach, especially under adverse circumstances encountered in rea-world driving, should be done.
Perhaps it is time for the people to call the NHTSA to account, to tell the NHTSA to really justify their INaction with regard to the RLMS approach to automotive rear lighting. Perhaps it is time to show with well conceived testing that their opinion regarding the non-importance of rear light color is correct. Or maybe it's not correct ... especially during adverse moments encountered in real-world driving.
How about the times when a light appears to be ON only because sunlight is being strongly reflected by an external, colored plastic lens? This can be on the rear of a vehicle ahead OR on a traffic signal light during daylight driving. External lenses on the rear of automotive vehicles, and on traffic signal lights, should reflect sunlight only as white colored light. Then, whenever a color other than white is seen, you can know for sure that the light IS on. The use of color to distinguish reflected sunlight would be very effective in at least decreasing, hopefully eliminating, an always aggravating, sometimes dangerous, uncertainty about light illumination during daytime driving.