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String Christmas lights are bulbs mounted at intervals along a single flexible wire that plugs in as one strand. They are the most common form of Christmas lighting — the strands you wrap around a tree, clip along a roofline, or drape indoors — and the category spans many bulb sizes and both LED and incandescent versions.
How string lights work: bulbs, wire, and spacing
The design is simple and unchanged for decades. Bulbs are wired at even intervals along a two- or three-conductor wire, and the whole strand plugs into an outlet or into another strand. The spacing between bulbs, the bulb size, and the wire color vary by set, but the wire-and-bulb layout is what makes it a string light. Most modern sets add connectable ends so you can link strands end to end, plus a fused plug that protects the run if a bulb shorts. That connectability is why one outlet can power a whole tree.
String light bulb types: mini lights, C7, C9, globe, and fairy lights
The bulb decides the look and the best use, so this is the choice that matters most.
| Bulb type | Size & look | Best for |
|---|---|---|
| Mini | Small, spaced points of light | Christmas trees and garland |
| Fairy | Tiny bulbs on thin wire | Accents, jars, walls, inner-tree glow |
| C7 | Strawberry-size bulbs | Rooflines and small trim runs |
| C9 | Larger bulbs, bold from the street | Rooflines, big outdoor displays |
| Globe (G40) | Round café-style bulbs | Patios, railings, boutique looks |
The bulb types and colors guide maps every style to its ideal use, and what are fairy lights covers the delicate thin-wire subset in depth.
LED vs incandescent string lights
String lights come in two technologies. LED string lights use light-emitting diodes that run cool, sip power, and last for many seasons, and their low draw lets you connect far longer runs from one plug. Incandescent string lights use a heated filament for a warm, familiar glow that some people prefer up close, but they run hot, use more electricity, and limit how many strands you can safely chain. For efficiency, safety, and long connectable runs, LED wins, which is why our best LED Christmas lights guide recommends them for most displays.
Connectable warm white and multicolor sets
Within either technology you choose a color. Warm white gives a cozy, classic glow, cool white reads crisp, and multicolor is festive. Connectable ends let you link several warm white or multicolor strands into one run from a single plug, up to the maximum connectable count printed on the tag.
String lights vs cluster lights and net lights
Standard string lights space bulbs evenly along the wire, which makes them versatile for trees, rooflines, and long runs. Cluster lights bunch many LEDs tightly for a dense, continuous glow, and net lights arrange bulbs in a grid you drape over bushes or hedges for even coverage. Each solves a different problem: string for reach and versatility, cluster for density, net for fast, even bush coverage. Compare the two most-confused styles in cluster lights vs string lights, and see what are net Christmas lights and what are cluster Christmas lights for the alternatives.
Outdoor string lights: waterproof, GFCI, roofline, and Christmas tree use
String lights split into indoor-only and outdoor-rated sets. Outdoor string lights are sealed against moisture and labeled waterproof or weather resistant, which is what a roofline, fence, or outdoor Christmas tree needs. Plug outdoor string lights into a GFCI outlet, use outdoor-rated extension cords, and keep the plug connections off the ground and out of standing water. Indoor-only string lights are not sealed and should stay inside on the tree or along a mantel.
Choosing and using string lights
Start with the job: a tree wants mini lights or fairy bulbs, a roofline wants C7 or C9, a patio wants globe. Match the wire color to the surface, pick warm white or multicolor to taste, and choose LED for efficiency and long runs. For a Christmas tree specifically, our best Christmas tree lights roundup covers full sets, and for how to size the count see how many lights for a Christmas tree. Browse the full tree and indoor lights category for more.
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