It's confusing at Wiki....
Quote:
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Seven-segment displays can be found in patents as early as 1908 (in U.S. Patent 974,943, F W Wood invented an 8-segment display, which displayed the number 4 using a diagonal bar). In 1910, a seven-segment display illuminated by incandescent bulbs was used on a power-plant boiler room signal panel.[5] They did not achieve widespread use until the advent of LEDs in the 1970s.
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That link is to the patent for Wood's eight segment display which is clearly illuminated by incandescent bulbs. If the later boiler room seven segment display was also lit with incandescent bulbs, what the hell lit the earlier seven segment display?
