Christmas Lighting · Buyer's guide

LED vs incandescent Christmas lights, and C9 vs C7: what to have installed

Updated September 13, 2026

If a professional is hanging your holiday lights, the bulbs will almost certainly be commercial-grade LEDs, and the size that goes along the roofline will almost certainly be C9. That is the short answer. LEDs draw a fraction of the power of incandescent bulbs, run cool, survive weather and handling far better, and let one circuit carry a much longer run, which is why they are what installers stock and what a seasonal display is built around. The decisions that are still yours are the ones that change how the house looks: bulb size, spacing, finish, and colour temperature. This guide walks through each, so that when an installer asks "C9 warm white, 12-inch spacing, faceted?" you know what you are agreeing to.

LED versus incandescent: what actually differs

Incandescent Christmas lights make light by heating a filament until it glows. LEDs make light by passing current through a semiconductor. That single difference explains almost everything else.

The one honest argument for incandescent is the look. A hot filament gives a warm, slightly amber glow that some people prefer, especially on older homes. Early LEDs deserved their reputation for looking blue and clinical. Modern warm-white LEDs do not; a 2700K LED is very close to an incandescent bulb to most eyes, and it is the colour temperature professionals specify for a traditional display. If the amber look is what you want, say "warm white, 2700K" rather than asking for incandescent. You get the look without the heat and the failures.

The practical case for LEDs is the run length. Because each bulb draws so little, an installer can run hundreds of feet of roofline from a single outdoor outlet without tripping a breaker or chaining extension cords across the yard. On an incandescent display the same house needs the run split into sections, each fed separately, with the wiring to match. That is more labour, more cords, and more places for a connection to fail in the rain.

Why installers supply the bulbs

Some homeowners ask whether the installer will hang lights they already own. Some will, on a straightforward roofline, and the cost guide explains how that changes what you pay. But the standard professional service is pro-supplied, and the reasons are not about margin.

• Commercial-grade construction. The strings installers carry are built for repeated install and removal: heavier-gauge wire, sealed sockets, bulbs that lock rather than push in. Retail strings are built to survive one season on a shelf and one on a house.
• Custom lengths. Professional roofline lighting is typically socket wire cut to your house, with bulbs placed at the chosen spacing, rather than fixed-length strings joined end to end. Corners land where corners are, and there are no dark gaps or doubled-up sections.
• Matched colour. Bulbs from one batch match. Two retail boxes bought a year apart often do not, and a colour shift halfway along the eave is the first thing a visitor notices.
• Accountability. If a section fails in December, an installer who supplied the lights can fix it with matching stock. An installer hanging your lights can only tell you a bulb has gone.

Many seasonal installers do not sell you the lights outright. They keep them, store them, and hang them again next year. If that is new to you, read the rental guide before you compare quotes, because it changes what the price includes.

C9 versus C7: the size question

The C in a bulb name stands for the cone shape, and the number is the diameter in eighths of an inch. A C9 is nine-eighths of an inch across at its widest, roughly the size of a thumb; a C7 is seven-eighths, closer to a large grape. That small difference in size is a large difference in how they read from the street.

The rule of thumb installers use: the further the viewer is from the light, the bigger the bulb. A two-storey colonial set back on a lot wants C9 along the roofline. A single-storey ranch close to the street can carry C7 without looking sparse, and C9 on it can look heavy. Many displays use both: C9 on the main roofline and ridge, C7 on porch rails, dormers and window frames where the larger bulb would crowd the trim.

The two sockets are not interchangeable. C9 bulbs fit an E17 base and C7 bulbs an E12, so the size decision is made when the socket wire is cut, not when the bulbs go in. An installer who quotes C9 has stocked C9 wire; changing your mind after the run is built means rebuilding it.

Mini lights and C6

Mini lights, the small pre-wired strings most people grew up with, and C6 bulbs, the smallest of the cone family, belong on greenery rather than architecture: wrapped around tree trunks and branches, woven through shrubs, along garland. They are too small to define a roofline from the road. A professional display commonly uses C9 or C7 on the structure and minis on the plantings, and the two together are what makes a house look finished rather than outlined.

Spacing, finish and colour

Three more choices decide the look, and installers will make them for you unless you ask.

• Spacing. Twelve-inch spacing on C9 is the default because it reads as a clean line of separate points from the street. Nine-inch reads as a denser, brighter line and uses a third more bulbs. Fifteen-inch is lighter and more traditional. Ask to see photos of each on a house like yours; the difference is bigger than the numbers suggest.
• Faceted or smooth. Faceted bulbs have a cut-glass surface that sparkles because each face throws light in a different direction. Smooth bulbs glow evenly, closer to the old incandescent look. Faceted is the common professional choice for LED C9 because it hides the single point of light inside the bulb; smooth suits a softer, vintage display.
• Colour temperature. Warm white around 2700K is the traditional choice and pairs with brick, stone and wood. Pure white, around 5000K or higher, reads crisp and modern and pairs with grey, white and dark trim. Mixing the two on one house is the most common mistake in DIY displays; decide once.
• Multicolour. Red, green, blue, orange and warm white in rotation, or a two-colour pattern. Ask whether the sequence repeats cleanly at corners; a good installer plans the bulb order so the pattern does not stutter where runs meet.

Pre-wired strings versus socket wire

Retail Christmas lights come as fixed-length strings with the bulbs permanently attached. Professional roofline lighting is more often built from socket wire: a spool of weatherproof cable with empty sockets at a set interval, cut to length on site, with bulbs inserted afterwards. The socket-wire approach is what allows the custom lengths, the exact corner placement and the bulb swaps described above. It also means a failed bulb is a bulb, not a string: you replace one, and the run carries on.

The trade-off is that socket wire is a professional material. It needs plugs fitted, runs planned within the wire's rated load, and a clip system to hold it to shingles, gutters or fascia. That is the work you are paying for when you hire, along with the ladder time. If you are comparing a professional quote against doing it yourself with boxed strings, you are comparing two different products, not two prices for the same one.

What to tell an installer

You do not need to specify everything. You need to know enough to answer the questions and to recognise a good answer. Tell the installer what the house is made of and what colour the trim is, whether you want traditional or modern, and which parts of the house matter most to you from the street. Then ask:

1. Which bulb size and spacing are you quoting, and why for this house?
2. Warm white or pure white, and what colour temperature?
3. Faceted or smooth?
4. Are the lights yours or mine after the season, and is takedown and storage included?
5. How is the run powered, and will it need more than one outlet?
6. What happens if a section fails in December?

Installers are listed by state and city under Christmas light installers, and a city page such as Denver shows who covers a specific area. If you are weighing a permanent system instead of hanging lights each year, the permanent Christmas lights guide covers what changes.