Short Answer: Incandescent Christmas lights (the glass kind with filaments) last about 3000 hours.
Longer Answer: Because incandescent Christmas lights generate heat by heating up a tiny filament, their lifespan is not as long as their LED counterparts.
Expect about 3000 hours which is about 125 days or a little over 4 months of operation if you leave your lights continuously plugged in.
(We actually suggest you turn off your lights during the day, and after it gets late to extend the lifespan of your light strings.)
The following environmental conditions can shorten the life of your light strings:
- Exposure to weather extremes - either too hot and too cold
- Exposure to salt in the air. Beach living is hard on lights and anything else stored outside (or inside for that matter!)
- Exposure to snow
- Critters and squirrels chewing the wires
- Installation location where wind can move the stings and cause rubbing that will put wear and tear on the wiring
- Sun exposure will take a toll on the insulation
- Surges and fluctuations in the electrical supply
- Quality of electrical power source - hydroelectric and geothermal power generation generally have more impulses than coal, natural gas, or nuclear power generation
Our favorite tip for extending the lifespan of your incandescent Christmas lights is to replace burned out bulbs as soon as you notice failures. Each bulb that is burned out uses less electricity which is distributed to the lit bulbs. Too many burned-out bulbs and your lights will experience cascade failure.
Be sure to replace burned out bulbs at the end of each season. If you purchase a large number of light strings of a single type, consider purchasing one extra strand to be a future source of replacement bulbs.
Hope this helps. Have any questions? Post them in the comments below.