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Light bulb question (might be too complex for some of you, experts only)

  1. May 31, 2007 #1
    ok, I know I always think my questions are going to be dumb, but this time I should really get some credit for how dumb it is. but I can't find the answer on the internet so here goes:

    This little lamp I have says "max 25W," does this mean that the maximum output of the lamp is 25W, so a higher W bulb won't shine very bright? or does it mean that a higher W light bulb would cause it to catch fire or something?

    ... I really know nothing about hardware (yes, a light bulb is hardware to me; you don't even want to know my horror stories from car-fixing class in high-school, my mark was 17% and it was a class I actually showed up to).
  2. jcsd
  3. May 31, 2007 #2

    Chi Meson

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    This one.

    The "wattage" (power) is the rate at which energy is dissipating from the bulb, mostly in the form of infra red "heat" radiation. A 25 W lamp is not designed to deal with any greater rate of heat output. Melting or at least discoloration would occur.
  4. May 31, 2007 #3
    hey i guess this wud help
    25 watts means that the heat generated across the filament of the bulb is equivalent to 25W, that is due to the current flowing in the filament, which if we take I and R as the resistance of filament gives I^2 * R(also equal to V^2/R) as the energy(or heat). now bulbs r caliberated on the basis of the resistance of filament, so the actual way of measuring the lightening ability shd be resistance but it is not (bcoz of some issues that u know). so R is selected as such that the current it takes from the supply (voltage supply is constant, well almost) does not melt the filament material. therefore a higher wattage lamp has a filament of lesser resistance but is more thick then the lesser wattage one, bcoz the higher wattage bulb has to dissipate more heat, thicker filament has a more surface area to dissipate heat..
    so u see, only the filament properties(like resistance n its thickness, length) is the deciding factor for the power rating of the lamp.
    but dude i might be wrong, i hav just explained it on basic principles, u need an expert opinion n u atleast had a car fixing class, i still didnt.
    n filament never catches fire, it melts n the same 25W bulb ll shine bright when connected to a 440V supply then when it is connected to 110V supply, but it ll melt in the case of 440V supply.. hope u got ur answer
  5. May 31, 2007 #4
    In my opinion, it is not a matter of "melting the bulb". Melting can in principle occur, and of course your bulb will not handle 1 kW, but it is irrelevant. The bulb has been designed to have an optimal brightness at a given value of the power consumption. Using another power will mainly affect the efficiency of your bulb.
  6. May 31, 2007 #5
    thanks guys! I guess I'll get that 40W out of there.

    :rofl: thanks anyways. though this is obviously a question only an expert who has attended several years of electrical-thingy-making classes can answer.
  7. May 31, 2007 #6
    nah dude, i m a mech engg student n that too in my 3rd year, i m still just a lil sweet kid. not much sweet though

    n i m not sure that filament ll melt or what, i havent ever done it, but i wud like to do it, but again my dad wont allow me to
  8. May 31, 2007 #7


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    Good plan! At best, you'll damage your fixture through discoloration or melting of the cover on it with a higher wattage bulb, and at worst, start a fire. It won't instantly destroy the light unless you do something really extreme like put a 100 W bulb in a 25 W fixture, but it's certainly not something you want to leave on for a long time, and not ever unattended.
  9. May 31, 2007 #8


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    Don't put in a brighter bulb than the fitting or shade specifies. You might burn down your house. I've known it happen.
  10. May 31, 2007 #9
    This is a very basic question, and it could be answered by someone who did well in High School physics. I also know some people who have PhDs but would fumble to answer it. I mention this to show the fallacy of asking for advice from 'experts only', it is up to you to judge the quality of the answers you recieve.
  11. May 31, 2007 #10


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    It also helps to have had a couple electrical-thingy-destroying classes. Those are pretty fun electives! :devil:

    The other reason not to use a larger power rated bulb is that the life of the bulb will be shortened. The lamp is marked for product liability reasons, however (as described already), not to save you money on bulb replacements.
  12. May 31, 2007 #11


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    :rolleyes: Some people need to replace their sarcasm detectors.
  13. May 31, 2007 #12
    it's the internet! it ruins all my jokes! :cry: there should be a special sarcasm font.
  14. May 31, 2007 #13

    Chi Meson

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    FOR CRYIN OUT LOUD. Did no one notice my CORRECT response? POST #2!


    Hey Moe. You got that Mission of Burma yet?
    Last edited: May 31, 2007
  15. May 31, 2007 #14


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    Yes, but I think some people may have misread it, thinking "it" was the bulb, not the lamp....of course some people call bulbs lamps anyway....
  16. May 31, 2007 #15


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    Humor is lost on the interweb...
  17. May 31, 2007 #16
    haha, yea thanks.

    :approve: it's going to take more than one or two good 80's bands to make up for this:

    and there's just no excuse for this:

    ... though it might still all have been worth it, for this:
    Last edited by a moderator: Sep 25, 2014
  18. Jun 1, 2007 #17
    not just electrical, all the DIY= destroy it yourself experiments are cool.
    nah humor is not lost, its all so much fun here
  19. Jun 1, 2007 #18

    Chi Meson

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    Here they are. This is them after regrouping. Sound is not the best, and Colin seems to go off key at one point. But this song was out in 1981, and that's when the music of the 90s began.
    (since this is Moe's thread, and since the OP was insignificant, I think we can go off topic to a previously established discussion.)
    Last edited by a moderator: Sep 25, 2014
  20. Jun 1, 2007 #19
    do you REALLY think that we've covered all the intricacies of light-bulb wattage requirements?!

    That is pretty 90's sounding, I dig their live show. Most MTV bands suck live now a days; they put them on huge tours so early in their career that they never learn how to put on a proper show.

    Probably the best band I've seen live is queens of the stone age, their shows are just kick-ass in a jar.
    I saw this band called "throw rag" open for them once and their live show was insane too, watch this if you want to see the greatest washboard solo ever about 2 minutes in:

    that poor kid they bring on stage looks really nervous :rofl:. their CD sucks but their live shows are awesome.
    Last edited by a moderator: Sep 25, 2014
  21. Jun 2, 2007 #20
    hey what happened to the bulb question.. can anyone tell me if i was right or wrong?
    everybody here is busy here talking of some video. this is a PHYSICSforum
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