The best Christmas light testers, and what each one cannot fix
Half a string goes dark because one bulb failed in a series circuit. The right tool finds it in a minute — if it works on your kind of light.
By Sawyer V. · Published
A string of mini lights with one dark section is the most common Christmas lighting fault, and the one most often solved by throwing the string away. A repair tool finds or bypasses the bad bulb in a minute and saves the set — and on a pre-lit tree, it saves the tree.
The tools are specific about what they can fix, which is the most useful thing about them. Five below.
Wreath & Watt earns a commission on qualifying purchases made through the Amazon links on this page. It costs you nothing and it does not change the order of the picks — here is exactly how we are funded.
Quick picks
| # | Product | Best for | Score | Price |
|---|---|---|---|---|
| 1 | No imageLight Keeper Pro, incandescent mini light repair toolPulses the set to fix failed shunts, plus bulb and fuse testers | Incandescent mini lights and pre-lit trees | 7.8/ 10 | Check price #ad · Disclosure |
| 2 | No imageLED Keeper Pro, LED light set repair toolRepairs LED light sets, with published exclusions | LED strings | 7.8/ 10 | Check price #ad · Disclosure |
| 3 | No imageHoliday light tester for LED and incandescentTests both LED and incandescent | Finding the dead bulb on either type | 5.5/ 10 | Check price #ad · Disclosure |
| 4 | No imageHLS TEST-200 mini light tester and repair gunMini light tester and repair gun | A second tool for the other hand | 4.8/ 10 | Check price #ad · Disclosure |
| 5 | No imageLED Light Keeper, LED light repair toolLED repair tool, no limitations publishedSkip this | Skip | 3.5/ 10 | Check price #ad · Disclosure |
Scores are our own weighting of published manufacturer specifications, explained in full on how we research. They are not test results. We have not tested these products.
The picks in full
#1 — Incandescent mini lights and pre-lit trees
Light Keeper Pro, incandescent mini light repair tool
Pulses the set to fix failed shunts, plus bulb and fuse testers
7.8
/ 10
The pick for incandescent strings and older pre-lit trees. The limitations list is honest; read it before you buy.
Published specifications
- Works on
- Incandescent mini light sets, including icicle, net, pre-lit trees and wreaths
- Method
- Plug into an empty socket, pull the trigger to fix the shunt
- Also includes
- Audible continuity detector, bulb tester, fuse tester, bulb puller, storage compartment
- Spare bulbs
- 2.5 V, 170 mA
- Does not work on
- LEDs, control-box sets, rope lights, battery sets
- Voltage
- 120 V only
Our scoring
- Fixes the common fault
- 10 / 10
- Published limitations
- 10 / 10
- LED support
- 1 / 10
- Spec completeness
- 10 / 10
Good
- Fixes the most common failure — a bulb whose shunt did not close — without finding the bulb first
- Publishes exactly what it cannot fix, which is rare and useful
Watch out
- Incandescent only; it does nothing for LED strings
- No help with sets on a control box
Specs from the Amazon listing (ASIN B002DGM9V2), verified 2026-09-11.
#2 — LED strings
LED Keeper Pro, LED light set repair tool
Repairs LED light sets, with published exclusions
7.8
/ 10
The pick for LED strings. Check yours is series-wired mini-light construction before relying on it.
Published specifications
- Works on
- LED Christmas light sets
- Does not work on
- Parallel-wired sets, control boxes, thinner micro-wired LEDs
Our scoring
- LED support
- 10 / 10
- Published limitations
- 10 / 10
- Accessories
- 4 / 10
- Spec completeness
- 7 / 10
Good
- The LED counterpart to the Light Keeper Pro, for the strings most people now own
- Publishes what it will not fix
Watch out
- Excludes parallel-wired and micro-wire LEDs — check your string's construction first
- Fewer published accessories than the incandescent tool
Specs from the Amazon listing (ASIN B0D5MXVM91), verified 2026-09-11.
#3 — Finding the dead bulb on either type
Holiday light tester for LED and incandescent
Tests both LED and incandescent
5.5
/ 10
Buy it if you own both kinds of string and mostly need to find the dead bulb.
Published specifications
- Works on
- LED and incandescent lights
- Function
- Tester
- Repair
- Not stated in the listing
Our scoring
- LED and incandescent
- 10 / 10
- Repair function
- 3 / 10
- Published detail
- 4 / 10
- Spec completeness
- 5 / 10
Good
- Works on both LED and incandescent, where the repair tools each work on one
Watch out
- A tester, not a repair tool — it finds the fault; you still replace the bulb
- Little else published
Specs from the Amazon listing (ASIN B083752K35), verified 2026-09-11.
#4 — A second tool for the other hand
HLS TEST-200 mini light tester and repair gun
Mini light tester and repair gun
4.8
/ 10
A reasonable alternative to the Light Keeper Pro for incandescent minis. The Light Keeper publishes more.
Published specifications
- Format
- Tester and repair gun
- Works on
- Mini lights
- LED support
- Not stated in the listing
Our scoring
- Function
- 8 / 10
- LED support
- 2 / 10
- Published detail
- 4 / 10
- Spec completeness
- 5 / 10
Good
- A tester and repair gun in one, from a holiday lighting supplier
Watch out
- LED support not stated
- Little else published
Specs from the Amazon listing (ASIN B003YO273M), verified 2026-09-11.
#5 — skip this
LED Light Keeper, LED light repair tool
LED repair tool, no limitations published
3.5
/ 10
Our skip. For an LED tool, the exclusions list is the most useful spec, and this one does not give it.
Published specifications
- Works on
- LED Christmas lights
- Limitations
- Not stated in the listing
Our scoring
- LED support
- 8 / 10
- Published limitations
- 1 / 10
- Published detail
- 2 / 10
- Spec completeness
- 3 / 10
Good
- An LED repair tool from the same family as the Light Keeper Pro
Watch out
- Publishes nothing about which LED constructions it cannot fix
- The LED Keeper Pro publishes its exclusions
Specs from the Amazon listing (ASIN B009SDS6QK), verified 2026-09-11.
How we ranked these
Published compatibility and limitations first, then function — repair, or test only.
| Tool | Incandescent | LED | Repairs | Limitations published |
|---|---|---|---|---|
| Light Keeper Pro | Yes | No | Yes, plus testers | Yes |
| LED Keeper Pro | Not stated | Yes | Yes | Yes |
| LED + incandescent tester | Yes | Yes | Test only | No |
| HLS TEST-200 | Yes | Not stated | Yes | No |
| LED Light Keeper | Not stated | Yes | Yes | No |
Two tools publish what they cannot fix. That list is the most useful spec in the category.
Source: Manufacturer listings on Amazon.com, verified September 2026.
Why one bulb darkens a section
The arithmetic
- Light Keeper Pro spare bulbs: 2.5 V each, published
- 120 V household supply / 2.5 V = 48
- So about 50 bulbs share one series circuit
An incandescent mini string is wired in series sections of about 50 bulbs. When one bulb fails and its internal shunt does not close, the whole section goes dark — which is exactly the fault these tools are built to find.
The full diagnostic sequence, from fuses to connectors, is on Christmas light troubleshooting.
For incandescent strings and pre-lit trees
The Light Keeper Pro plugs into an empty socket and sends a pulse through the section that closes the failed shunt, so the rest of the section lights and the dead bulb shows itself. It also carries a bulb tester, a fuse tester, a continuity detector and a bulb puller. It publishes that it works on icicle and net lights and on pre-lit trees and wreaths — and that it does not work on LEDs, control-box sets, rope lights or battery sets.
For LED strings
Most strings bought in the last decade are LED, and the LED Keeper Pro is the tool for them. If you own both kinds and mostly need to find the dead bulb rather than bypass it, the LED and incandescent tester covers both — it tests, it does not repair.
Saving a pre-lit tree
A pre-lit tree with a dark section is the most expensive thing these tools save. An incandescent pre-lit tree is the Light Keeper Pro’s best use; for LED pre-lit trees, check the exclusions before relying on the LED tool. How long pre-lit lights last in the first place is on how long Christmas lights last, and the pre-lit trade-off on pre-lit vs unlit.
Questions
›Why is half my string of lights out?
Mini strings are wired in series sections of about 50 bulbs. One bulb whose shunt did not close darkens its whole section. A repair tool finds or bypasses it.
›Does the Light Keeper Pro work on LED lights?
No. It publishes that it works on incandescent mini sets and does not work on LEDs, control-box sets, rope lights or battery sets. There is a separate LED tool.
›Can a light tester fix a pre-lit tree?
The Light Keeper Pro publishes that it works on pre-lit trees and wreaths with incandescent mini lights. For LED pre-lit trees, check the LED tool’s exclusions.
›Tester or repair tool?
A tester finds the dead bulb; a repair tool also bypasses the failed shunt so the section lights. One tool here only tests, but works on both LED and incandescent.
Sources
- Light Keeper Pro listing (ASIN B002DGM9V2) — Incandescent mini sets incl. pre-lit trees; shunt repair, bulb and fuse tester, continuity detector, bulb puller; 2.5 V 170 mA spares; not for LEDs, control boxes, rope or battery sets; 120 V
- LED Keeper Pro listing (ASIN B0D5MXVM91) — LED light set repair; not for parallel-wired, control boxes or thin micro-wired LEDs
- LED and incandescent light tester listing (ASIN B083752K35) — Tests LED and incandescent lights
- HLS TEST-200 listing (ASIN B003YO273M) — Mini light tester and repair gun
- LED Light Keeper listing (ASIN B009SDS6QK) — LED Christmas light repair tool
- Series-circuit arithmetic — 120 V divided by the published 2.5 V spare bulb rating — our arithmetic
We have not tested these products. Every figure above comes from a published manufacturer specification or from arithmetic shown on this page, and anything a maker does not publish is printed as unavailable rather than estimated. How that works, and what we will not claim, is set out on how we research.