[quote name=\'Fedya\' date=\'Feb 7 2004, 12:31 PM\'] In the middle of the match, the power went out, but because the weather was good and it was an outdoor match, play continued. The vane displays didn't go dark; they simply remained at whatever they displayed at the time of the power outage. I'm wondering whether the lines that make up the numbers in the vane displays aren't actually light bulbs. (By the same token, if the power were to go out in the old Family Feud studio during Fast Money, would the display go dark?)
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The display you are talking about is an electromechanical one, as is the Feud board and the Clark $25K/$100K Pyramid readouts.
The way the numerical ones work, each segment is a flat piece of plastic painted with a highly-reflective paint, usually florescent yellow or white. They are hooked up to electromagnets such that when a segment is needed to form a number (or not), a single pulse rotates the segment so that the surface is visible, or out of the way so that it isn't (at that time it's actually rotated 90 degrees so it's perpendicular to the surface of the readout).
In the case of the Ferranti-Packer Feud board, each "pixel" on the board is a small disc, painted on one side, black on the other. A pulse is sent to a "pixel" dependent on which side it needs to display to make a particular board element, be it a letter, number, or part of the big Feud logo. You see the same thing on a lot of city bus systems, and stadium marquees, and stuff like that.
These types of readouts are popular because they are a) durable, as you don't have to go replacing light bulbs, and b) energy-efficient, because the only electricity is used to change the state of the board...maintaining it, as you saw in that tennis match, takes nothing.