To use, simply hold down the black button and move the tester down the length of the light set so that the sensor is near the top of each bulb. The red indicator will light when near a functioning bulb, but will not light when near a faulty bulb.

Also, is there a tester for Christmas lights? Theres a way to test (and fix) the entire string of miniature lights without testing each bulb individually. Try the LightKeeper Pro (www.lightkeeperpro.com). If the shunt fails, it knocks out the lights in the section. The electricity sent by pulling the trigger locates and fixes the defective shunt.)

Regarding this, what is the best Christmas light tester?

The Christmas Light Tester – Our TOP 5!

CHRISTMAS LIGHT TESTER QUALITY OUR OVERALL RATING Light Keeper PRO 5 5 GKI Bethlehem Lighting Deluxe Consumer Mini Christmas Light Set Tester 4 3.6 Westinghouse 4 Function Christmas Light Tester 4 3.6 TEKTON 7333 Battery, Bulb and Fuse Tester 5 4.3
Why does only half of my string of lights work?

Dont pull too hard on the wires. A loose bulb, broken socket or frayed wire is sometimes all it takes for the strand to malfunction. After taking down the lights, plug them in before storing them, to make sure they still work. Newer style LED (light-emitting diode) lights are the exception.