How To Repurpose Old Christmas Lights Into Custom Keyboard Backlighting

Every January, millions of strands of Christmas lights are unplugged, coiled, and stored away—many destined for landfills when they eventually fail. But what if those twinkling strands could live a second life? With a little creativity and basic electronics knowledge, you can transform outdated holiday lights into a personalized, energy-efficient backlight for your mechanical keyboard. This project not only reduces electronic waste but also gives your workspace a unique aesthetic that store-bought RGB kits can’t match.

The idea isn’t just about recycling; it’s about reimagining. Old incandescent or LED Christmas lights contain usable components: wires, connectors, resistors, and light sources. By extracting and modifying these, you can craft a soft, ambient glow beneath your keys. Whether you're drawn to warm white tones from vintage bulbs or colorful LEDs for a retro vibe, the result is a functional art piece tailored to your setup.

Why repurpose Christmas lights instead of buying new?

Purchasing a pre-built RGB underglow kit is convenient, but it comes at an environmental and financial cost. Most kits use newly manufactured components, contributing to resource extraction and plastic production. In contrast, repurposing existing materials reduces demand for new products and keeps functioning electronics out of landfills.

Additionally, older Christmas lights—especially incandescent mini-lights—emit a warmer, softer light than many modern LEDs. This quality is ideal for subtle backlighting that enhances visibility without straining the eyes during late-night typing sessions. Plus, using mismatched colors from multi-colored strands can create a nostalgic, pixel-art-style glow that feels more personal than uniform factory lighting.

Tip: Test each bulb or LED segment before disassembly. A strand with 80% working lights still offers plenty of usable components.

Tools and materials checklist

Before starting, gather everything you’ll need. Most items are common in household toolkits, though a few specialized tools ensure precision and safety.

1. Soldering iron and solder (lead-free recommended)
2. Wire strippers and cutters
3. Multimeter (for testing voltage and continuity)
4. Heat shrink tubing or electrical tape
5. Small screwdrivers (for opening keyboard case)
6. Hot glue gun or double-sided tape (for securing lights)
7. Repurposed Christmas light strand (preferably 50–100 lights)
8. USB power source or keyboard PCB with available 5V output
9. Needle-nose pliers and tweezers
10. Insulating mat or non-conductive work surface

If your keyboard lacks exposed 5V/GND pads, consider using a spare USB cable to draw power directly from your computer. Always disconnect power before making connections.

Step-by-step installation process

Follow this sequence to safely convert your old lights into functional keyboard illumination.

1. Assess and test your Christmas lights

Plug in the strand to identify working sections. If only parts of the string light up, isolate those segments. For incandescent sets, check for broken filaments. For LEDs, look for darkened or cracked casings. Use a multimeter in continuity mode to verify connections between bulbs.

2. Disassemble the strand

Carefully clip bulbs or LEDs from the main wire, leaving 2–3 inches of wire on each side. Avoid pulling, which can damage internal leads. For molded plastic sockets, gently pry them open with a small flathead screwdriver to extract the bulb assembly.

3. Determine voltage requirements

Most mini Christmas lights operate at low voltages—typically 2.5–3.5V per bulb. Incandescent strings often run in series, while LEDs may be wired in parallel or short series groups. Use the multimeter to measure the forward voltage (Vf) of individual LEDs if possible. This helps match them to your keyboard’s 5V supply.

Light Type	Voltage Per Unit	Typical Configuration	Keyboard Power Compatibility
Mini Incandescent	2.5–3.5V	Series (e.g., 20 x 2.5V = 50V total)	Not direct; requires resistor or driver
LED Mini Lights	2.0–3.2V	Parallel or short series (2–3 in series)	Often compatible with 5V via resistor
Commercial RGB Kit	5V standard	Direct USB-powered	Fully compatible

4. Modify for 5V operation

If using incandescent bulbs, they likely require higher voltage than your keyboard provides. In this case, focus on salvaging only the wires and connectors. Instead, reuse individual LEDs from LED-based Christmas strands, which are easier to adapt.

For each LED, calculate the appropriate current-limiting resistor using Ohm’s Law: R = (Vs - Vf) / I, where Vs is 5V, Vf is the LED’s forward voltage (e.g., 2.8V), and I is desired current (e.g., 20mA). Example: (5 - 2.8) / 0.02 = 110 ohms. Use a 120-ohm resistor per LED if wiring individually.

5. Plan the layout

Open your keyboard case and examine the space beneath the PCB. Decide whether to place lights around the perimeter, under the spacebar, or both. Avoid areas with switches or exposed circuitry. Sketch a rough diagram showing where each light will go.

6. Wire and connect the LEDs

Arrange LEDs face-down along the chosen path. Solder wires to connect them in parallel: all positive leads to a single red (5V) line, all negative to black (GND). Add resistors to each positive leg before connecting to the main power line. Secure joints with heat shrink tubing.

7. Connect to power source

Identify a 5V and ground pad on your keyboard’s PCB—often labeled “VCC” and “GND.” If unavailable, splice into a spare USB cable (red = 5V, black = GND) and route it through the case. Solder carefully and insulate all connections.

8. Test and secure

Reconnect the keyboard and power it on. Observe brightness and evenness. If some LEDs are dim or flickering, check solder joints and polarity. Once stable, use hot glue or foam tape to fix the lights in place. Reassemble the case, ensuring no wires are pinched.

Tip: Use diffuser materials like parchment paper or translucent plastic between LEDs and keycaps to soften glare and spread light evenly.

Real-world example: Reviving 1980s icicle lights

Mark, a hobbyist in Portland, Oregon, inherited a box of vintage Christmas decorations from his grandparents. Among them were two strands of red-and-green “icicle” lights from the early 1980s—bulky, hand-wired, and partially non-functional. Rather than discard them, he extracted the three dozen working green bulbs, which used 3V incandescent filaments.

Knowing they couldn’t run directly on 5V, Mark removed the glass enclosures and tested the filaments. He then wired them in series pairs (6V total) and added a 10-ohm balancing resistor to drop excess voltage. Using thin gauge wire, he arranged the paired bulbs along the top edge of his HHKB-style keyboard. Powered via a USB breakout, the setup produced a soft, vintage glow visible only in dim lighting—a subtle nod to family tradition every time he typed.

“It’s not bright,” Mark said, “but it’s meaningful. Every time I see that green shimmer, I think of December mornings at my grandma’s house.”

Expert insight on sustainable electronics

“Repurposing e-waste isn’t just a hobby—it’s a necessity. Over 50 million tons of electronic waste are generated globally each year, and less than 20% gets recycled properly. Projects like converting old lights into functional components teach people to see value beyond the original design.” — Dr. Lena Torres, Sustainable Electronics Researcher at MIT Media Lab

Dr. Torres emphasizes that creative reuse extends product lifecycles and builds technical literacy. “When someone learns to desolder a bulb or calculate resistance, they’re not just fixing a light—they’re gaining autonomy over their devices.”

Common pitfalls and how to avoid them

• Overloading the USB port: Adding too many LEDs can exceed current limits. Stick to 10–20 modified LEDs unless using an external regulator.
• Short circuits: Exposed solder joints touching metal cases can fry your motherboard. Insulate thoroughly and double-check connections.
• Inconsistent brightness: Mixing different LED types or skipping resistors causes uneven output. Use matched components when possible.
• Heat buildup: Incandescent bulbs generate heat. Avoid placing them near plastic parts or enclosed spaces.
• Irreversible modifications: Permanent alterations may void warranties. Document changes and keep original parts.

Frequently asked questions

Can I use smart Christmas lights for programmable effects?

Yes, but with limitations. Some modern LED strands use proprietary controllers incompatible with standard keyboard signals. However, addressable LEDs (like WS2812B types) found in newer sets can be reprogrammed using Arduino-compatible code. You’d need to reverse-engineer the data protocol and integrate it with open-source firmware like QMK, which is advanced but feasible for experienced modders.

Will this void my keyboard warranty?

Almost certainly. Opening the case and modifying internal components typically voids manufacturer warranties. Proceed only if the keyboard is out of warranty or considered expendable. Consider practicing on a cheap donor board first.

Are incandescent bulbs safe inside a keyboard?

They can be, with caution. Incandescent bulbs reach temperatures of 60–80°C under operation. Ensure they are mounted away from heat-sensitive plastics and have airflow. Limit usage to short durations or use a timer switch. For continuous use, LEDs are safer and more efficient.

Final thoughts and next steps

Transforming old Christmas lights into keyboard backlighting blends sustainability, craftsmanship, and personal expression. It’s a reminder that functionality doesn’t end when a product’s original purpose fades. With careful planning and attention to electrical safety, even seemingly obsolete electronics can find new roles in our daily lives.

This project scales well—from a simple underglow using three LEDs to a full rainbow array powered by salvaged controllers. As you gain confidence, consider integrating motion sensors, light-dependent resistors for auto-dimming, or even sound-reactive circuits using leftover strand components.

🚀 Ready to breathe new life into your holiday lights? Dig out that old strand, fire up the soldering iron, and start building a keyboard that’s uniquely yours. Share your results online—your creation might inspire others to rethink what ‘waste’ really means.