When half of your Christmas lights go out, the cause is usually a tripped circuit breaker, a blown fuse in the plug, or a burnt-out or loose bulb that breaks the circuit. Check each one in order, and you can usually get your lights working again in minutes.

C6, C7 and C9 Christmas lights differ mainly in size and brightness. C6 bulbs are the smallest, C7 bulbs are mid-sized and great for trim, trees and bushes, and C9 bulbs are the largest and brightest, which makes them ideal for rooflines and big trees.

Christmas lights began with Yule logs and candles on trees. The first visible LED was created by Nick Holonyak Jr. at General Electric in 1962, and after bright white LEDs arrived in the 1990s, LED Christmas lights reached stores in the early 2000s. Here’s how they evolved.

If your Christmas lights aren’t working, the usual causes are a bad or loose bulb, a blown fuse in the plug, a tripped breaker or faulty outlet, or moisture in outdoor connections. Test your lights before hanging them and check these problems one at a time.

Some Christmas lights run on 12 volts, but most don’t. Traditional incandescent lights are made for 120-volt household power and need a power inverter to work from a 12-volt battery. Many LED lights come in 12-volt versions that plug straight into batteries and off-grid setups.

Incandescent Christmas lights usually last about 1,000 to 2,000 hours of use, or a few holiday seasons with normal use. How long yours last depends on how many hours a day they’re on, the weather they face, and bulb quality. Regular checks and careful storage help them last longer.

Yes, you can use C9 LED bulbs in most old C9 light strings, as long as the sockets are the standard E17 size. Before switching, check older strings for frayed wires, corrosion or worn insulation, since damaged wiring can cause flickering or become a safety hazard.

Christmas lights come in many types, each with its own best use. C6 bulbs suit garlands, wreaths and trees, C7s outline roofs and paths, and bright C9s light up large areas. Mini LEDs, G12 globes, string lights and icicle lights each add their own look to your display.

Outdoor Christmas lights can stay plugged in during rain if they’re rated for outdoor use, plugged into GFCI outlets, and their connections are protected from water. Use weather-resistant, safety-certified lights, cover plugs and connectors, and never overload the circuit.