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This Is Why Light Bulbs Are Round

Who put the "bulb" in light bulb?

The average American household has more than 40 separate sockets for light bulbs. However, despite the ubiquity of this illuminating technology, the light bulb's shape is a bit of a mystery, even to its regular users. Why, after all, a bulb? Why not a light cube? Or a light prism?

Well, according to Derek Porter, an associate professor of Lighting Design at Parsons, the reason—like many engineering feats—is one of "technical, practical considerations" focused around the bulb's capacity for lighting up a room.

As those paying attention in geometry class may recall, a sphere is the only shape in which the center is equidistant from all points on the surface. In other words, there is no shortcut from the center of a sphere to its outer edges—all paths are the same length. Now, when it comes to a bulb, especially of the frosted variety, it's very important that the tungsten filament—the horizontal piece providing the light— is equally distant from all points on the bulb. This is because, Porter says, in a bulb, the frosted surface—rather than the tungsten—essentially becomes "the light source itself."

Thus, in order for it to produce the "even, omnidirectional distribution of light" that illuminates our rooms, the tungsten filament needs to be at the "center point" of the bulb, showering each of its edges with an even intensity of brightness. Given that the bulb's first manufacturers—working around 1879—were no dummies when it came to mathematics, they understood that the easiest way to achieve this result would be to produce bulbs in a rounded shape, placing the filament in the center.

In recent years, however, many light bulb buyers have moved away from the original, incandescent bulb with its tungsten filaments to LEDs and CFLs, both for their energy- and and money- saving qualities. Yet, despite no longer needing to ensure the proper relation between a piece of tungsten and the outer edges of the bulb, many bulbs remain in the original, teardrop shape. The reason, Porter says, is the standardization common in manufacturing.

When the original bulb was produced, companies needed to make reflector systems—the parts which house and direct the light of the bulb whether in a ceiling or a lamppost—that fit the shape of the bulbs being produced at the time. To achieve the even distribution of light that consumers wanted, this typically called for a rounded, parabolic shape. Over time, these constructions became standardized for the industry, so that even "as the technology has become more refined," Porter says, the bulb's shape "continues to follow that early pattern based upon its compatibility with these engineered systems."

If that all sounds rather high-tech, Porter provides a more easily-digestible example. Even "something as elemental as the spring clip that holds the shade over your table lamp," he says, helps determine the form that light bulbs take—and will continue to for the foreseeable future. And for more fascinating facts about the things that populate your daily life, don't miss these 27 Amazing Facts About Household Objects. 

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