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Testing for Faulty Bulbs

Occasionally a section of lights may go out in your Artificial Christmas Tree. This is typically the result of a bulb that has become loose from the socket. When this is the case, a standard light tester designed to check for current is all that is needed to locate the bulb that needs replacing. Many tree owners find themselves confused as to how they should operate their light tester, and are unsure as to exactly what they need to look for. Below is a basic guideline to help you test for faulty bulbs.

Anatomy of a Light Tester

Light testers are included with every prelit incandescent artificial Christmas tree sold at Christmas Lights, Etc. The light tester consists of a red and green LED light, and a green pointed tip.

Interpreting the Light Tester Results

  • Red Light: Indicates a bad bulb that is receiving current, but is stopping the flow of current through the light string.
  • Green Light: Indicates a good bulb which is continuing to pass current down the string.
  • No Light: Indicates that no current is reaching the bulb. The bad bulb will precede a bulb that has a result of no light on the tester.

Using the Light Tester

  • The best method for testing the light string is to move from branch to branch to spot check the bulbs.
  • Insert the green pointed tip between the two wires that come out of the socket. Move any additional wiring out of contact with the light tester, ensuring the only wires touching the tester are the two wires attached to the socket.
  • Press the green testing button
    • If the result is a red light, you have immediately found a bad bulb. Replace the bulb with a new bulb.
    • If the result is a green light, move down a branch and try another light. Continue to move down the branch in sections until the tester results in no light. Somewhere between a result of a green light and a result of no light will be the bad bulb, which results in a red light.
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Additional Troubleshooting

If results from the light tester failed to result in red or green lights, there may be no current in the string or multiple bulbs are out, and additional steps must be taken.

  1. Remove the light string power plug, rotate the plug half a turn, and plug back in. This step will reverse the polarity, causing the light tester to result in a red light reading when it reaches the first of the bad bulbs. This step will only work if there is still a flow of current in the wire.
  2. Inspect all light strings for damage to the insulation on the wire and loose wires around the sockets and electrical plug. Also check for damaged sockets and electrical plugs. If you find a damaged string you should discard it.
  3. If multiple strings are out, individually plug each string into a power source to begin testing. It's easier to isolate a bad string if only one string is connected rather than multiple strings.
  4. Check to see if the string has a fuse in the power plug. If the entire string is out you could possibly have a blown fuse.

Understanding One Light Goes Out Technology

"One Light Goes Out, Rest Stay Lit" is a technology that uses an internal shunt within the bulb to continue the flow of electricity throughout a light string, even if a bulb has burned out. It is important to understand that if the shunt is broken when a bulb breaks, or if it is dislodged due to a loose bulb, the flow of electricity will stop. Additionally, each mini light has two small copper wires that come out of the base of the bulb, and fold upwards on each side. When the socket is in place and the bulb is secure, this allows for the current to continue to flow. Sometimes the copper wire may be broken or out of position, and replacing the bulb or moving the copper wires into place should remedy the problem.

We advise everyone to test for faulty bulbs before storing their artificial Christmas tree for the year. Proper storage of Christmas trees also helps to prevent wear and tear on mini lights.


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