Christmas is a joyous time filled with decorating, gift giving, and getting together with loved ones. One of the central parts of Christmas decor is the beautiful Christmas tree, with its colorful lights and ornaments. However, it can be incredibly frustrating when one or more of the lights on your Christmas tree goes out, leaving an unsightly dark spot. When this happens, how do you know which light bulb to change?
Check for burnt out bulbs
The first step is to visually inspect your Christmas tree lights to locate any burnt out bulbs. Burnt out bulbs are easy to spot – they will appear blackened or cracked. Start at the top of your tree and work your way down systematically, looking at each light bulb as you go. Pay special attention to any strings of lights that are entirely out, as this indicates there is a bulb within that string that has burnt out and caused the whole string to stop working.
Use a continuity tester
If visually checking doesn’t reveal the burnt out bulb, the next step is to use a continuity tester. A continuity tester is a device that detects breaks in the electrical circuit of your Christmas lights. To use a continuity tester:
- Unplug the string of Christmas lights.
- Separate the light strands, unwinding them from the tree branches as needed.
- Plug the lights back in.
- Touch the two probes of the continuity tester to the metal contacts at the bottom of each bulb one at a time.
- The tester will light up or beep if the bulb is good. If it remains dark and silent, you have found your burnt out bulb.
Once you locate the bad bulb, unplug the lights, remove the bulb from the socket, and replace it with a spare that matches the wattage and shape. Plug the lights back in to ensure the replacement bulb works.
Use a multimeter
A multimeter is another tool you can use to diagnose burnt out bulbs in Christmas lights. To test each bulb:
- Unplug the lights and separate the individual strands.
- Set the multimeter to test for continuity.
- Touch the multimeter probes to the metal contacts at the bottom of the first bulb. The multimeter should beep or display 0 ohms resistance if the bulb is good.
- If the multimeter does not beep or register 0 ohms, that bulb is burnt out. Mark it for replacement.
- Continue testing each bulb until you locate the bad one(s).
The benefits of using a multimeter over a continuity tester is that it gives you an exact resistance reading, whereas a continuity tester simply tells you good or bad. However, a continuity tester is generally faster and easier to use.
Use the half test
If you don’t have a continuity tester or multimeter available, you can use the half test method. This involves systematically testing half strands of lights at a time to isolate the bad bulb:
- Unplug the lights and detach the strands from the tree.
- Plug one half of the strand in and check if it works.
- If it works, the burnt out bulb is in the other half. Unplug and set this working half aside.
- If it’s not working, the burnt out bulb is in this half. Leave this half plugged in and unplug the other half.
- Take the half that’s not working, divide in half again, and repeat the testing process until you’ve narrowed it down to just a few bulbs.
- Visually inspect the suspect bulbs and replace the one that appears burnt out.
- Plug the full strand back in to test all the lights.
While not as direct, the half test method can help isolate the bad bulb through logical elimination.
Look for telltale signs on the wires
Sometimes a burnt out bulb is obvious based on externally visible cues. Check the wires between bulbs for these signs of a faulty light:
- Darkened or melted wire – If you notice the wire between bulbs appears melted or blackened, this points to a short circuit from a faulty bulb overheating.
- Bent or loose filaments – Inside the bulb, you may see the tiny filament is loose, sagging, or bent. This delicate filament heats up to emit light, so any interruption can cause a bulb to fail.
- Broken filaments – Similarly, if the fine filament inside appears fully broken or snapped, that will lead to a burnt out bulb.
- Discolored or cracked bulb – The plastic bulb housing may appear burnt, blackened, cracked, or otherwise damaged around a bad bulb.
- Loose bulb – Check that the bulb is screwed securely into the base. If loose, tightening it may restore the connection and relight that bulb.
Focus your visual inspection on the areas around bulbs that are out to spot these type of external indicators of a fault.
Consider issues with Decorative Bulbs
If you are using decorative Christmas light bulbs other than standard mini lights, there are some additional considerations for finding and replacing burnt out bulbs:
Large Bulbs
Larger bulbs such as C7 and C9 size have more obvious filaments that make it easier to visually identify if the filament is broken inside the bulb. Look for gaps or breaks in the delicate filament wire inside a darkened bulb.
Odd Shaped Bulbs
Christmas lights come in all shapes from flames to flowers. Check that each plastic bulb housing is seated properly in its base. If loose, gently twist the bulb so the pins realign and tighten it into the base.
LED Bulbs
LED Christmas lights have a reputation for reliability, but they can still burn out. Look for any bulbs that appear darker than others. LEDs gradually dim over time before going out completely.
Bubble Lights
For vintage bubble lights, if the internal fluid has emptied out from a breach in the seal, the bulb may no longer have the heat transfer needed to glow and bubble. Gently remove the bulb, seal any leaks with glue, and replace the fluid.
EliminateVoltage Issues
In addition to burnt out bulbs, voltage issues can also lead to lights going out on your Christmas tree. Here are some voltage problems to check for:
- Overloaded outlet – Too many strands plugged into a single outlet can cause the lights to short out or dim from inadequate power. Try plugging strands into different outlets to spread the load.
- Damaged wire – Frayed or cracked Christmas light wires can lead to voltage drops or intermittent power to some bulbs, making them turn off. Replace damaged cords.
- Loose plug connections – Check that the prongs on the plug are making a snug connection in the outlet and extension cords. Tighten if needed.
- Bad fuse – Older light strands have fuses in the plugs that can wear out over time. Replace the fuse with a new one of the same amp rating.
- Prototype issues – With new lights, manufacturing defects may cause some bulbs to malfunction right out of the box. Return these for replacement.
Checking for voltage problems can help determine if there are issues beyond just burnt out bulbs causing your lights to prematurely go dark.
Replace Old Lights
If you find you constantly have to hunt for burnt out bulbs and replace them in a set of Christmas lights, it may be time to retire those old lights and invest in a new set. Light technology has come a long way, even just in the last decade. Replacing dated incandescent lights with modern LEDs can provide many benefits:
- LED Christmas lights last up to 10 times longer than incandescents. They use less energy and run cooler, meaning fewer burnt outs.
- LEDs are available in more color options like warm white, multicolor, and color changing.
- LED light strings can come pre-connected rather than having to be individually screwed in like old incandescent lights.
- Newer LED designs distribute the lights more evenly on the wires to disperse voltage better and prevent bulbs from burning out prematurely.
While still an investment, new Christmas lights will save time, frustration, and money in the long run by avoiding frequent burnt out bulbs. The latest lights stay brighter longer and create a more dazzling display.
Conclusion
Finding and replacing burnt out Christmas lights is an annoying but inevitable holiday chore. By systematically checking lights using visual inspection, continuity testers, and the process of elimination, you can troubleshoot problems quickly. Ruling out voltage issues, properly handling decorative bulbs, and replacing old lights can also cut down on future burnt outs. With some diligence and testing, you can keep your Christmas tree aglow with light this season.
