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| When was the first electronic bitmap sign invented? |
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| tooki:
Umm, aren't all incandescent bulbs filled with inert gas? |
| james_s:
--- Quote from: tooki on April 11, 2020, 08:10:11 pm ---Umm, aren't all incandescent bulbs filled with inert gas? --- End quote --- No, most under about 50 watts are vacuum filled. In small lamps with thin filaments the convective losses of a gas fill become more significant than the increased rate of tungsten evaporation you get with a vacuum filled lamp. |
| tooki:
Huh, ok! I guess that explains why when I was a minor (in the 80s/90s), better flashlight bulbs expressly said they were xenon or krypton filled. I guess the cooling from the gas either let them burn brighter, or keep them cooler to make them more shock resistant? |
| james_s:
Ordinary household lightbulbs typically use an argon/nitrogen mix fill, the increased pressure reduces the evaporation of tungsten in the same way that a pressure cooker raises the boiling point of the water within. This allows the filament to be run hotter, producing a brighter, more efficient lamp with higher color temperature while still achieving reasonable lifespan. Xenon and krypton accomplish the same thing but these gases are far less thermally conductive so they allow very small lamps to be gas filled without making them horribly inefficient (relative to vacuum) by excessive convective and conductive cooling of the tiny filaments. Krypton or xenon are very expensive compared to argon and nitrogen so combined with diminishing returns in larger/higher wattage bulbs it is not economical so it was rarely used. The hotter you burn a filament the more efficient the bulb, but the faster it burns out. Varying the voltage has a roughly linear effect on efficiency but an exponential effect on lamp life, hence the occasional bulb you hear about famously burning for 100+ years, or the once common photoflood bulbs that were rated to last 6 hours. Making a bulb last hundreds of thousands of hours is easy, but the reason it wasn't widely done is that the resulting bulb will be very inefficient. Contrary to the beliefs of some it was never a conspiracy to sell more bulbs, rather manufactures knew that electricity costs a lot more than bulbs so the typical 750-1,000 hours lifespan of a household incandescent lamp was settled on as a compromise between efficiency and lifespan. |
| @rt:
Certainly not the oldest, but I still have a Z80 driven sign, with it’s associated DMA controller. How lovely :D Two colour LEDs ranged in alternating columns used to create 16 colours, so long as the text is moving. Different display, but this thread also reminded me of my favourite thread in the whole world: https://www.eevblog.com/forum/repair/progressive-gaming-neurizon-led-sign/?nowap |
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