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

Light waves from a normal house hold globe effecting a dc circuit. Why?

  1. Aug 8, 2012 #1
    Hello. Im new to electronics and physics. Since injuring my back at work, I now have a lot of time on my hands to learn about the things that facinate me. So please forgive me for any wrong terminology or spelling and grammar mistakes.
    I have recently made a small jacobs ladder using a lm555 ic tip50 transistor and a old ignition coil, all powered from a small 12v battery. I wired the transistor up using bedini method. A diode between the base and the emitter and a ne-2 neon globe from collector to emitter to protect the transistor. Under normal use of the jacobs ladder with the house hold lights on and/or during the day the ne-2 in the circuit glows/flashes rapidly (i believe it is using some of the back emf to illuminate showing excess energy being used by the ne-2). Running the jacobs ladder at night i turned the house lights off so i could see the sparks more prominantly and i noticed that the ne-2 globe stopped flashing when ever i turned off the house lights and would begin to flash/glow whenever i turned the house lights back on. So i experimented with turning a light on in the background so only low level light from the house light was reaching my jacobs ladder circuit and the ne-2 globe would flash slower or glow alot dimmer.
    So in full light the ne-2 glows brightly in low light the ne-2 glows less brightly and in no light the ne-2 goes completely out.
    I have come to the conclusion that light waves from the house hold lights are effecting my seperate dc circuit powered by a 12v batt. But because i know nothing about light waves energy particles i thought i would put it to the experts to maybe help me explain what is happening in my circuit. Is whats happening, a well known reaction/relationship between light waves and energy particles of a circuit? Or have i stumbled across something new? I have put a youtube video about it up called "Help jacobs ladder in a b...." Please disregard the item i used for the glass chamber it was the cheapest solution i could get a hold of to protect from shock etc.
    I would greatly appreciate any input or explanation. Also im happy to answer any questions and post circuit diagram etc.
    Please check out my clip:
    Last edited by a moderator: Sep 25, 2014
  2. jcsd
  3. Aug 8, 2012 #2


    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    hi calvinator
    Welcome to PF :)

    I cant think of anything obvious that would cause that effect.

    I couldnt look at your video the link didnt appear to work correctly

  4. Aug 8, 2012 #3
    Last edited: Aug 8, 2012
  5. Aug 8, 2012 #4

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper

    I can see the video fine ... you can clearly see the effect.

    Though I would expect the JL to be sensitive to external EM. Maybe your kitchen light fitting has a loose contact generating some EM like a spark gap?

    Try it during the day with the kitchen light off too. With another light source - say, a desk lamp or a torch.
  6. Aug 8, 2012 #5
    During the day the ne-2 is always glowing. At night with the 12v overhead hallogen globe it effects the circuit. And with a normal 240volt globe it also effects the circuit. It doesnt effect the operation of the JL. To me it looks like any light wave changes the energy particles in the area/atmosphere that is illuminated causeing excess radient energy or what ever its called to enter my circuit hence the ne-2 glowing. When there is no light, energy particles behave randomly as per usual causing no excess particle to enter my circuit. That is the conclusion i came up with but i am a novice. With the 12v kitchen lights there is one transformer that is not working which could cause some EM. But this is not the case for the laundry light. I will try it at night with a torch etc and report back to you. Thanks for the input.
    Last edited: Aug 8, 2012
  7. Aug 8, 2012 #6
    Your construction is rather crude and their looks to be too many variables to just look at a video to determine the cause to the effect. Try isolating components and providing contacts that are properly insulated as well as ensure good grounding. Would be interested in the results.
  8. Aug 8, 2012 #7
    Thanks for the reply. I will construct the circuit more robustly and ensure good grounding. As for the contacts/probes they run about an inch apart through a solid rubber grommit. I cannot think of how to make that any better. I dont understand how to isolate the components as i need all of them for my circuit to run. But i can insulate them more, Regardless of that please correct me if im wrong, it still shows that a light source is effecting the circuit eg. Daylight with no lights on has the same effect as having a light on at night. Any suggestions would be great.
  9. Aug 8, 2012 #8

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper

    Yeah - this is one of those cases where I get itchy to go get hold of the setup.

    If you just run the Ne globe off a weak AC, nothing else: simplest possible circuit ... do you still get the same effect.

    Note: if the regular incandescent bulb was run in the same socket, it does not rule out the possibility of something in the wiring generating EM. The JL does seem to me to be flickering a lot.

    "energy particles" is an ambiguous term ... light energy is carried by photons.
    There are mechanisms to get a current by shining light on things but nothing that would be so big-an effect. You can try covering different parts of the setup to see which bit appears light-sensitive.

    You can get a florescent bulb to light in the presence of EM fields ... you'll have seen demos with Tesla coils etc. So, if I had to bet, I'd still look in that direction. Try repeating in a different location.
  10. Aug 8, 2012 #9
    Light will not affect your circuitry unless you have photoelectric components in your circuitry. The primary culprit for me is still EMI caused by the afore mentioned construction. It is a rather neat issue though.
  11. Aug 8, 2012 #10
    Excellent feedback. I will try all of your suggestions. And post a wiring diagram/schematic so you can test for your self. I have tried this indoors and outdoors. Same results and i have tried in different rooms and had same results. Does a photon have magnetic flux? Can you you effect a light wave with magnemotive force? What happens to the suns light waves when it gets close to the earths magnetic field? Obviously i dont know much but i find this all so facinating. I have only started teaching myself electronics and physics for the last 6 months but im obsessed. So any and all suggestions are always appreciated greatly.

    knowledge is power.
  12. Aug 8, 2012 #11
    I would suspect that light can be affected by things such as magnetomotive force or electromotive force; however, I know for sure that light can be bent by gravety. The two forces mentioned (if possible) would require great amounts of energy to effect the direction of light. However and once again the type of effect that you are proposing is not likely. Light is a particle made of wavelengths. It is basically a particle of change. In other words it has volume (so it acts like a particle); but, has no mass. It sorta exists but doesnt. And its really hard to study something that moves or changes that fast. I still think that only gravety and time effect light travel.
  13. Aug 8, 2012 #12
    Thank you. Your a wealth of knowledge. Here is a copy of my schematic. For any one who wants to try replicate. I will do some more testing and learning. Please feel free to give any more information or tips. I will post my results after trying all of your suggestions.

    Attached Files:

  14. Aug 8, 2012 #13
    Ok i have done some more testing. Took it all outside and had the same results with the front door light. The i tried with a torch, keeping the torch at the same distance away and just angling the torch towards and away from the circuit essentially shining light on and off the circuit. Same results. The torch is a led torch with two different sources for light click the button once light come on the side click the button twice light comes on the end of the torch. So i was able to keep the torch in exactly the same position and distance away. By clicking it on once, light shone on the circuit having the same effect. Clicking the button twice made the light shine away from the circuit but kept the torch in exactly the same position. Neon globe goes out (same results) ruling out any emf. And to be sure i tried it with just a plain bic lighter. Same results. So no magnetic interference definately. So i isolated some of the components to see which ones were being effected by the light source. The closer the lighter was to the diodes (1n4004) the brighter the neon glow's. It also had an effect close the resistors. So i need to be able to isolate them better to get definative results. But with a crude circuit and crude testing it looks like the diodes are photo sensative. Does anyone know if 1n4004 diodes are meant to be photo sensative? I will continue testing and refine my circuit/ability to isolate components. Your advice and information was very helpful. Any more input or advice? Thanks
  15. Aug 8, 2012 #14

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper

    1. you have only ruled out emf from the light source. I'd have lost the bet.
    2. No the 1n4004 is not supposed to be photoreactive... nor are your resistors.

    Try a dark cloth or a box to block light to the suspected photoreactive components - see if the effect goes away.
  16. Aug 8, 2012 #15
    Thank you. I will do more testing tomorrow and post the results.
  17. Aug 8, 2012 #16


    User Avatar
    Science Advisor

    You should have posted this in one of the physics forums, someone would have recognized it straight away. This is a classic example of the photoelectric effect.

    The voltage being induced must be just barely enough to allow the neon tube to conduct. Photons from the ambient light sources provide extra energy to the cathode's electrons, making them more easily pulled away from the cathode surface and able to initiate conduction of an arc or gas discharge.

    Hertz actually discovered this effect in quite similar circumstances during the late 19th century. He was studying radios wave caused by a spark gap and when he darkened the room to better observe the weak sparks in his receiver, he also noticed that the sparks either stopped or became much weaker.

    At the time Hertz noted the effect, but didn't investigate the cause in any detail. It was more of an annoyance to him, something that was hindering his radio wave research, rather than a breakthrough discovery. Einstein however did very detailed research on the cause of this "photoelectric effect" in the early 20th century, in what is now considered some of the most important pioneering work in establishing the fundamentals of quantum physics.
    Last edited: Aug 8, 2012
  18. Aug 8, 2012 #17

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper

    I asked around ... there is a photo-sensitive component: the neon tube itself.

    Look up photoionization :)
    Basically the neon bulb is almost at the threshhold of producing light using the current it's supplied, however not quite. Additional light is enough to "stimulate" the neon sufficiently to push it over the threshold. This is essentially the same process that occurs with the photoelectric effect with metals. In the case of a gas, the term photoionization is more common. (Which is why I discounted it earlier - I was thinking of metals, and didn;t thing light from a lamp would ionize the gas silly me: the tube is wired to a voltage source.)


    In discussion with +Stuart Young
  19. Aug 8, 2012 #18


    User Avatar
    Science Advisor

    Hi Simon. The photon energy of visible light only extends up to about 3eV. ([itex]E= h c/\lambda[/itex]). This gives about 3 eV for blue light of lambda = 400 nm.

    The work function of common metals is around 3 to 5 electron volts while the first ionization energy of neon is around 21eV.

    Of course the photon doesn't need to provide all of the energy, as the applied electric field is already close to ripping the electrons from the surface anyway. Given the energies involved however, I suggest it is far more likely the photoelectric effect at the neon bulb cathode is the main culprit here.

    Re my previous reply on this topic.
    Last edited: Aug 8, 2012
  20. Aug 8, 2012 #19
    Excellent. Thank you. Would you know of any text/ebooks that can give me detailed accounts of his study. Or just google? I have so much to learn.
  21. Aug 8, 2012 #20

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper

    You can just google "photoelectric effect"... it's very well documented. (It's what got Einstein his Nobel Prize.)

    I'm not going to argue the toss over where the photoelectric effect is occurring :) but I've certainly added to my understanding here.
    Something of a "doh!" experience.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook