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Thread: 230V Light bulbs

  1. #31
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    Ok, just to stir it up some more....
    A UK 100W light bulb is less bright than a US one. The lower current means the thinner filament loses heat faster in a UK bulb so the temperature at equilibrium is lower. If you really want BRIGHT incandescent, get a 6V 100W halogen. Run it off a universal input switchmode PSU and it won't matter which country you do it in.

  2. #32
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    Ok, I'l bite. If the filament is only thinner, and not thinner and longer, I would think the decreased radiant surface area would result in an INcreased temperature. can you explain?

  3. #33
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    Decreasing the filament size would cause a temperature increase for several reasons.

    1) You would be increasing the resistance of the lamp
    2) The surface area would also be decreasing (like you said) and therefore the heat dissipation would be greater. Same reason why power density is an issue for laserists. A 40 watt laser could be harmless to our eyes, if the power density is low enough.

  4. #34
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    Hmmm..you're still talking. Hmmm...ammm LOL
    I hired an Italian guy to do my wires. Now they look like spaghetti!

  5. #35
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    Quote Originally Posted by mliptack View Post
    Decreasing the filament size would cause a temperature increase for several reasons.

    1) You would be increasing the resistance of the lamp
    2) The surface area would also be decreasing (like you said) and therefore the heat dissipation would be greater. Same reason why power density is an issue for laserists. A 40 watt laser could be harmless to our eyes, if the power density is low enough.
    yes I agree, I was asking The_Doctor to explain his UK dimmer theory.

  6. #36
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    It's definitely right, trust me. You can verify it.

    Increased resistance alone would drop the power if the voltage stayed the same. What matters is that the consumed power is the same, 100 watts. The 240V filament must be thinner (and longer), because its resistance must be higher. It has more surface area for its mass, so thermal equilibrium happens at a lower temperature because more radiation can occur at that lower temperature than with less surface area in a lower-volt 100W lamp. The same amount of light is emitted, but it looks dimmer because more of it is wasted as IR, and the blue end of the blackbody spectrum is reduced as well. It isn't the output watts that are reduced, but the lumens, which is a measure of luminous efficacy, as judged by eyes, or meters that imitate them.

  7. #37
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    How would this apply to discharge lamps? I assume it wouldn't but I'm curious if there is something that maybe I am overlooking.

  8. #38
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    Pass.
    Not got much idea on those. As far as I know, the efficiency is based on an optimum pressure for a given voltage and tube length. I guess for a nominal power rating, they have similar efficiencies at 120 or 240, being made to work specifically. The heaters at the ends might make a difference, but I think those will only be powered during startup, to produce free electrons to start the arc.

  9. #39
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    Discharge light have a big bang at the beginning and then pretty normal voltage to keep the lights going.
    I hired an Italian guy to do my wires. Now they look like spaghetti!

  10. #40
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    HID Xenon gas lasers (miniature) would be very cool. Or Mercury Vapor..

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