- C9s are the bigger bulb and the professional standard for rooflines that are seen from the street.
- C7s are smaller and suit single-story homes, walkways, railings and close-up spots.
- They use different sockets: C7 has a candelabra (E12) base, C9 an intermediate (E17) base.
- In LED, either one costs little to run. The choice is about looks and viewing distance.
The difference in one table
| C7 | C9 | |
|---|---|---|
| Size | About an inch wide | About 1.25 inches wide, noticeably taller |
| Screw base | Candelabra (E12) | Intermediate (E17) |
| Typical incandescent wattage | About 5 watts | About 7 watts |
| LED wattage | Under 1 watt | Under 1 watt (about 0.96 W in Christmas Designers' example) |
| Best seen from | Close up | The street |
| Common uses | Walkways, railings, storefronts, small homes | Rooflines, gables, tree trunks, driveways |
Sizes from Christmas Designers; wattage varies by product – check the box.
When to choose C9
C9s are made to be seen from a distance. Christmas Designers describes them as the bulb that draws people in from down the street, which is why they are the default for rooflines, especially on two and three story homes where a smaller bulb disappears. If you are hiring a professional, expect C9s on the roofline unless you ask for something else.
When to choose C7
C7s look right where people see them up close: along a front walk, on porch railings, around a storefront window, or on a low single-story roofline where C9s can look oversized. They are also a good accent bulb alongside C9s – for example C9s on the roof and C7s on the path.
Spacing
Sockets are usually 8, 12 or 15 inches apart. Twelve inches is the common roofline choice; wider spacing gives a cleaner, more classic line and uses fewer bulbs. To count bulbs: feet of roofline × 12 ÷ spacing in inches. Our guide to measuring your roofline walks through it.
Stringers vs bulk line
Store-bought stringers come with bulbs attached and fixed lengths. Professionals mostly use bulk light line cut to the exact length of your roofline, fitted with separate retrofit bulbs that can be swapped when one fails. That is a big part of why a professional roofline looks tidier.
Keep reading
- Warm white, cool white or multicolour
- How to measure your roofline
- How much it costs to run Christmas lights
- Christmas light glossary
Sources
- Christmas Designers – C7 vs C9 Christmas lights – read September 22, 2026
- Christmas Designers – C7 vs C9 Christmas lights: when to use – read September 22, 2026
- Christmas Designers – How much do LED Christmas lights cost to run? – read September 22, 2026
Written by the Christmas Lights Outdoor Installation editorial team. Figures are dated and linked to their source; national numbers vary by area – confirm with local installers.
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