Calculator displays

<Gas discharge has the cathode suspended in the gas, and it is the gas <around it that glows, not the surface of the cathode. I have never seen <a blue one, but I imagine argon is more likely than mercury vapour <(which radiates mostly UV). Argon and mercury vapor are both UV emitters. Mercury vapor actually requires a heater to insure there is enough vapor. They have higher ignition voltages makeing them less suitable for semiconductor drive. Vacuum florescent was predominent with LEDs before LCDs displaced them. Vfs had low power, good brightness, suitable for multiplexing (nixies didn't) and operating voltages suitable for PMOS, CMOS and other semiconductor drives. The standard blue green VF would filter well to yellow, green or blue and with other phosphors red and a distinct deep blue were also done. The actual visible elemets of VF tubes could be a dot matrix, 7, 9 12, 15, 16 or more segments or even arbitrary shapes and complete words like "door open" or "overrange" as a single element. Nixie required far to much power for handheld and even the smallest were quite tall. There were variations of the nixie theme using bars but all of the high voltage needs remain and the classic neon orange color. Of the non crt display technologies I have that are in use and working: incandesent: Numitron 7segment flatface in my first freqcounter (1974). VF: alpha numeric with complete words, the loran used in my plane. VF: alpha dot matrix 40 char by 2 lines display system (C 1980) NIXIE: Yasu 355D 350mhz frequency counter. Nixie alpha: Burroughs 32 char selfscan as ascii right entry display. LED numeric: SR11 calc, various small frequency counters, DVMs and pannel meters. LED alpha: A display system using HP6508 15segment leds, 32 chars long. Allison