An Historian of Science Discovers the “Light Switch”

Historian and philosopher Emma Houston interrogates the science of electricity and light bulbs

The light switch was at the center of Houston’s first big foray into the history of electricity and lights. The story told in introductory electrical engineering textbooks is relatively simple: flipping the switch up turns the lights “on”; flipping the switch down turns the lights “off.” Whether a switch is in the on or off position has for for decades been seen as an expression of a light bulb’s “true” state or of “light itself.” It is the job of a science historian to discover where these stories come from, and why.

Houston’s doctoral dissertation, published in 2004 as Light Itself: The Search for On and Off in the Electric Circuit does just this, tracing the history of the idea that electromagnetic radiation is turned “on” and “off” by switches found on the wall. Early in the twentieth century, she shows, it was controversial to refer to “light switches” because sometimes electricians accidentally wired around them when installing lights.

But the fact that switches are visible, (unlike electricity) made them useful for enough to two groups of engineers–those building electrical circuits, and those working to untangle the role of electricity in light generation–that the association between switches and light solidified for decades.

Associating “light” with the “light switch,” writes Richardson, has serious consequences, as when engineers tried to develop a “super flashlight” that used two light switches and multiple batteries.

The “super flashlight” was finally abandoned in the development stage when engineers decided it was simpler to use bigger batteries, but in Light Itself, Houston argues that it made the light switch the star of electrical engineering in a way that still reverberates. She points to engineers like Professor Book, whose research focused for decades on using light switches to design home lighting plans. Such a focus was not inevitable, Houston argues: from the 1920s through the 50s, based on evidence in lasers, researchers saw buttons as drivers of light output.

It turns out that “light switches” do not actually cause bulbs to emit electromagnetic radiation. Engineers now understand that light, produced by incandescent bulbs as well as LEDs and compact fluorescents, is the result of numerous interconnected capacitors, resistors, power sources, and wire circuits that all work together. So called “light switches” do not cause light at all–they merely open and close light circuits, allowing electricity to flow (or not) to the bulbs.

But in an interview, Professor Book disagrees with Houston’s account. In Houston’s history, the super flashlight looms large in later researchers’ decision to focus on the switch, but Professor Book responds that research on the super flashlight “did not interest me, it did not impress me, it did not look like the the foundations of a path forward.” Building circuits around the light switch, he says, was not inspired by the popular image of a super bright flashlight with two switches, but “was simply the easiest way to design practical lighting for people’s houses” and that “flipping the switch does actually turn the lights on and off.”

Houston responds that of course we can’t expect actual engineers to know what inspired them or their fields, which is why we need science historians like herself to suss out what was really motivating them.

Author’s note: Professor Houston has degrees in philosophy and literature, but oddly, none in engineering or physics.

This parody is thanks to Harvard Magazine’s The Science of Sex: Historian and Philosopher Sarah Richardson Interrogates the Science of Sex and Gender.