PRE-WWII GLASS LENS TRIVIA

Prior to 1930, headlight lenses were generally flat, had the same left and right side pattern and very little prism. Twilite and Stabilite made attempts to create prisms. Also, most of the glass contained lead, and manganese, which reacted with UV rays to turn color; generally purple. By 1930 lenses began having optic prisms, and became convex. By 1933 headlight lenses had different left and right patterns to focus the projected light forward, and at a greater distance.

Tail lights, which had a red tint, also reacted to UV rays, but making the lens darker; which reduces visibility.
The function of headlights is to project and illuminate objects in front and to the side of the motorcar.
The function of the smaller (6-8 Watt) tail light, is to glow, to indicate the presence of the motorcar, to the following cars. Also, in that ever important braking event, the brake light glows. Light is NOT intended to be transmitted to the rear to illuminate following objects.

The headlights need to PROJECT light by the use of a 32 Watt bulb or greater, utilizing a focusing reflector, that transmits light, directed by a clear headlight lens with prisms. As the silver reflector ages, it oxidizes, losing efficiency.

I have seen a few people CHROME plate reflectors. Chrome actually absorbs light, not reflect it.
By 1940, the separate bulb/reflector/lens system was replaced by the sealed beam unit. Just a couple of marques and some trucks retained the non-sealed beam system into the 1940's.