What Are String Lights? Types, Sizes, and How LED String Lights Work

String lights are decorative light strings that run multiple bulbs along one flexible cord, and today most run on low-power LEDs.

A tangled strand on a patio railing sets a mood, lights a walkway, and stays on for hours. But the cord, wiring, and bulb style determine whether it’s safe to leave up, extend, or link. Understanding the parts makes later decisions easier.

What Are String Lights Made Of?

String lights are decorative lighting strings built from a flexible cord with multiple lamps or LEDs, per CPSC and CSA/UL-related materials treating them as seasonal and decorative lighting products. Wiring and bulb type split them into two families, which matters for how much power each string can safely carry.

Series-connected miniature strings wire small bulbs one after another. CPSC and CSA/UL-related materials note minimum conductor sizes of 22 AWG or 20 AWG depending on configuration, and 20 AWG with a polarized load fitting. Heavier insulation such as SPT-2W reduces shock and fire risk.

Parallel-connected strings with screw-base bulbs wire each socket independently. The same materials list minimum conductor sizes of 20 AWG or 18 AWG. Because sockets run in parallel, one dead bulb doesn’t cut power to the rest.

How Do LED String Lights Actually Work?

LED string lights are decorative fixtures where LEDs draw power through the string’s wiring and a controller or power source. Low-voltage DC designs are common in modular LED strands; commercial and outdoor versions are often built for direct AC connection.

Battery-powered versions trade cord length for portability. One manual lists 2m and 5m lengths with roughly 95mm (about 3.7 inches) of bulb spacing, though these vary by model and should never be assumed across brands.

Sizes, Spacing, and Connection Limits

String light sizes vary because they’re sold by use case, not one industry standard. Buying guidance commonly cites bulb spacing between 6 inches and 24 inches, with longer spacing covering more distance using fewer bulbs. Lengths range from 15 ft and 25 ft strands up to 48 ft and beyond, and LED counts run from 50 to 500.

Connection limits are where people get into trouble. One manual warns not to exceed 216 watts (1.8 amps) total when linking compatible strings end to end. A consumer safety guide states exceeding the manufacturer’s connectable limit creates fire risk — the tag is the authority, not the box.

How To Connect And Hang Them Safely

Reading the label before linking strands is the step almost everyone skips. The wattage and current tag sits within 6 inches of the plug on most products and is the only reliable source for that model’s maximum.

1. Find the tag near the plug and read the listed wattage or amperage.
2. If wattage isn’t printed, one manual says to calculate it from current using W = A × 120 for that product.
3. Add up the wattage of every string you plan to link and stay under the manufacturer’s stated maximum.
4. Use an outdoor-rated extension cord marked SJTW or SJTOW when powering lights outside.
5. Match the strand to its labeled environment — indoor, outdoor, or temporary seasonal use.

If you’re weighing options before buying, a tested roundup of great string lights for patios and porches compares styles side by side. For the underlying product rules, the CPSC’s proposed rule on seasonal and decorative lighting products covers how these products are classified.

Two limits catch people off guard. Not every LED strand is connectable — the allowable number of linked strings varies by model and must be checked on the label. And standards differ by product class and market; UL 588 is referenced in CPSC materials for seasonal lighting, but individual products may carry additional certification or regional rules.

Frequently Asked Questions

Can you connect LED strands from different brands?

Only if both products permit it. Compatible strings usually share the same plug style and wattage rating, and the combined total must stay under the lower of the two maximums. When labels don’t clearly match on voltage and connector type, run them on separate outlets instead of guessing.

Why do some strands stop working when one bulb dies?

Series-connected strings run power through each bulb in a chain, so a broken filament or loose bulb can interrupt the whole circuit. Parallel-connected strings with screw-base sockets don’t have that weakness, which is why they’re common where single bulbs are meant to be replaced.

Are battery string lights safe for outdoor use?

Only if the product is labeled for outdoor use. Battery packs and controllers are the vulnerable parts, so unless the manufacturer lists an outdoor rating and weather protection, keep battery strands under a covered porch or bring them inside during rain.