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Fluorescent Light Generator?

  1. Dec 1, 2003 #1
    Fluorescent Light Generator??

    Hi, I was recently reading up on the workings of fluorescent light bulbs, and I thought of an idea for using the bulb as an electrical generator. I know that inside the ballast of the light fixture, there is a small coil of wire that keeps the electrical current from going to fast through the bulb. I also learned that the gas inside the bulb itself, when excited with electrons, turns into plasma, which interacts with the phosphorous coating on the glass to make light. I also learned that unlike normal copper wires, when electricity flows through plasma, the resistance drops as the current rises because the excited ions continually release more electrons as the electricity flows through the gas. I was wondering if anyone knew if both the voltage and the current would rise inside the bulb if the control coil were not present to regulate the power flow. If both the voltage and current rise couldn’t one logically say that the bulb is outputting more power then it took to get it started? If this is true (and it’s purely hypothetical) couldn’t one create a circuit chip to keep the bulb lit and draw out the excess power instead of wasting it away in the control coil? I have absolutely no idea if this would work, but it was just an idea. Any thoughts?
  2. jcsd
  3. Dec 1, 2003 #2


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    Re: Fluorescent Light Generator??

    A coil of wire? An inductor? This won't regulate current.
    A fluorescent tube is nothing more than a tube full of low-pressure mercury vapor with electrodes on each end. When you pass current through the mercury vapor, the mercury atoms radiate ultraviolet light. The tube is coated with phosphor on the inside surface. The phosphor absorbs the UV light and radiates visible light.
    I don't think you fully understand the way a fluorescent tube controller works. I also am not sure what copper coil you're talking about.
    Forget about the voltage. What matters is the current. The more current passing through the vapor, the more light emitted. If the tube draws more current, it's using more power, turning that power into light. It does not make energy -- it dissipates energy provided by the plug you plug into a wall.
    No, of course not.

    - Warren
  4. Dec 1, 2003 #3
    Ok, first off, thank you for your reply. Here is the link to the source I used to find the information I'm talking about:


    I included some snipplets from the article so you can see where I got my information from.

    Here's the part about the gas in the bulb being a plasma:

    And Here's another section of the article that explains how the coil in the ballast works:

    I understand that the bulb has to have a constant input of elecreicity to keep it running but I was wondering about the effect the plasma/gas has on the output electrical current. I want to know if both the voltage and the current are rising in the bulb or just the current due to less resistance.

    Heres another refference that talks about the gas in the bulb being a plasma: http://www-istp.gsfc.nasa.gov/Education/wfluor.html

    Thank you for your reply and I look forward to your response :smile:
  5. Dec 1, 2003 #4


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    Right, simply exploiting the fact that current through an inductor cannot change instantaneously.
    Current in through one end of the tube = current out from the other. What 'output electrical current' are you talking about?
    The falling resistance means a lower voltage is necessary to establish a given current. Since current is what matters for a gas-discharge tube, as more gas is ionized, the applied voltage will go down. This is part of of what a ballast does -- it provides a large starting voltage to establish an arc. Once the arc is established, the ballast reduces the voltage significantly, and begins regulating the current.

    - Warren
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