Outside Bowled Frosted Tipped Light Bulb [Pre-1919]
Frosted light bulbs were manufactured in response to the complaints about the harsh glare coming from a clear or transparent light bulb, which was annoying and uncomfortable to many people, cast sharp shadows, and even presented a hazardous condition by making it difficult to see in the vicinity of the light bulb. One of the many attempts to resolve these problems was to paint the bulbs white on its outer surface in order to cut down on the glare. But this also appreciably reduced the amount of light and the paint itself would invariably flake off. A better method was to frost the outside surface of the bulbs on their hemispherical tops. Called “bowl frosting,” this method of frosting the bowl of the bulb was produced by either sandblasting the top, hemispherical surface of the lamp or by dipping the lamp into a tub of acid to etch the hemispherical top (while the neck and sides were left unfrosted) until the desired thickness of frosting was obtained. This left the surface with tiny, sharp crevices that gave the bulb its frosted appearance, a bit like that of the inside of the window pane on a frigid winter day. It is not clear when this method was first introduced, but outside bowled frosted bulbs before 1900 are known to exist. Although these bulbs did the job of diffusing the light more evenly and creating a softer glow, because of the resulting rough surface, outside frosted lamps were structurally weak and thus easily broken. The rough surface was also prone to collecting dust, which both made it difficult to wipe off and reduced the light output. This method of frosting was discontinued in 1925, when inside frosted light bulbs were introduced.