Sciency Words: Yehudi Lights (The First Cloaking Device)

Sciency Words: (proper noun) a special series here on Planet Pailly focusing on the definitions and etymologies of science or science-related terms.  Today’s Sciency Word is:


Last week, we talked about cloaking devices, a term and a concept that were invented by the writers of Star Trek.  But in fact, during World War II the U.S. military conducted experiments that rendered aircraft virtually invisible.  The technology came to be known as the Yehudi lights.

Yehudi Menuhin was a well-known Jewish violinist at the time.  There ended up being a running joke about him on Bob Hope’s radio show, spawning popular (and very annoying) songs like this one:

Basically, Yehudi became the name for some mysterious person whom no one could seem to find.  In this declassified military document, he’s referred to as “the little man who wasn’t there.”  This is offered as an explanation for why the Yehudi lights got their name.

Essentially, the Yehudi lights were an optical illusion. To quote from that same declassified document:

It is known from data on the visual acuity of the human eye that, at a distance of two miles, individual lights are indistinguishable as such, if their spacing is less than about four feet.

So by mounting lights on the wings and forward fuselage of an aircraft, and matching the color temperature of those lights to the surrounding sky, and flying the aircraft in just the right way relative to an observer, you could create the illusion of invisibility.  At least from a distance.  But by the time you got close enough to an enemy target that the enemy could see you, it was probably too late for the enemy to do much about it.

Getting back to the Star Trek  universe, there is a constant “arms race” going on over cloaking technology.  The Federation keeps figuring out new ways to detect cloaked ships; the Romulans and Klingons keep figuring out ways to make their cloaked ships undetectable again.  No one ever seems to hold the advantage for long.

As Mr. Spock says about the latest Romulan cloaking device: “Military secrets are the most fleeting of all.”  The same could be said about the Yehudi lights. They worked well enough, but only for a brief while.  Then RADAR came along, and the Yehudi lights became basically useless.

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