Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

I Is this just a normal fluorescence of glass molecules?

  1. Jul 5, 2018 #1
    hi guys

    i recently had built a HV power supply out of an old Flyback transformer i had laying around , i think it produces about 10KV ~ 15KV not very sure but it could arc at about ( 6mm in air ) ,

    and as you can see i tried to connect it to a 15W smal light bulb ( the positive terminal is connected to the strange looking rod you see on the left which is just touching the glass ) and i saw that strange effect .
    ( i don't know but i think its just the highly energetic electrons exiting the glass molecules which causes it to flurecence ) , give me your opinion on what is this ?! and could this apparatus produce xrays ?!
  2. jcsd
  3. Jul 5, 2018 #2


    User Avatar
    Gold Member

  4. Jul 5, 2018 #3
    the argon glow discharge is very far of this color plus i have another gas tube filled with argon and it produces a purple discharge thats a photo of it :
    the other glow is more of a yellowish green glow ( it doesn't seem to be glow discharge either ) its more like of a momentary flashes not a continios glow
    another thing i have to mention is that the filament is broken and its impacts rapidly with the glass of the bulb could this be the cause or anything ?!

    i just want to know these electrons are exiting what ?! because it doesn't seem to be the gas inside the bulb for some reason !
    unfortunately i dont have a prism or a diffraction grating .
  5. Jul 6, 2018 #4


    User Avatar
    Gold Member

    In the second picture you posted the color seems pretty close to the one I posted, :woot:

    It is hard from the pictures to see where the light is actually coming from, does it look like it comes from inside the bulb?

    More physics at work, neat! Electromagnetism at work?

    More small bulbs needed?
  6. Jul 7, 2018 #5
    yes! it comes from inside the bulb .

    what really confuses me is that the glow doesn't match any of the nobel gases glow discahrge :

    so , could this be from exiting the glass molecules or any thing ?!
    i read some where that the yellowish green glow in the glass is somewhat an indication of xrays ?! is that correct ?
    or i couldn't be producing xrays with relativaly low voltages ( 10 ~ 15 KV )
  7. Jul 7, 2018 #6


    User Avatar
    Science Advisor

    Perhaps a mixture of gasses? Break the bulb to find out if it is the glass.
  8. Jul 8, 2018 #7
    It looks somewhat like the glow discharge of krypton in the photo below. A special incandescent light bulb (A) filled with inert krypton gas is touching a plasma globe (B). A discharge occurs through the krypton gas in the light bulb, emitting greenish light. The spectrum of the discharge as seen by a hand spectroscope (C), corresponds with a krypton spectrum found on internet (D). Even the violet lines are present.

    So you might get a stronger emission from your 15 W light bulb by holding it next to a plasma globe.

    Last edited: Jul 8, 2018
  9. Jul 8, 2018 #8
    thank you spareine , krypton! i didn't see that one coming :) LOL
    but i have a question : isn't krypton is much more expensive than argon to use it for filling a regular light bulb ?
  10. Jul 8, 2018 #9
    Yes, the krypton light bulb cost about 2 euros, so it is more expensive than an ordinary bulb, but still within budget. :smile: I don't know whether krypton extends the lamp's life more than the cheaper argon, but I bought the krypton light bulb just for this experiment.

    (I bought a xenon light bulb as well (same price), and its glow discharge emits a similar greenish light, but I did not succeed in seeing its line spectrum through the spectroscope.)
  11. Jul 9, 2018 #10
    i searced online and , i saw that video on youtube :

    i was wondering is that green glow really indicates that xrays is being produced ?!
    becouse in my apparatus i think it might be the same glow , i tried to hold a neon indicator close to the bulb
    the neon indicator was flashing 20cm away from the bulb ?!
    and why xrays would produce such a glow ?!!
  12. Jul 10, 2018 #11
    I don't think you have x-rays being produced in your light bulb. It is unlikely that the gas pressure is low enough - 10-3 to 10-4 Torr is required for soft x-rays and your bulb is likely to have a gas fill at about 80% of atmospheric pressure. You can certainly get x-rays emitted from a television tube if your anode voltage is high enough, probably 30 kV or so would do it. Have a look at this link for more info


    Regarding krypton filled bulbs, I believe the switch to krypton was to allow a higher filament temperature and hence greater luminous efficacy than could be achieved with argon or a vacuum.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?