Christmas tree lights come in a variety of sizes, types and colors including C7 and C9 and miniature lights. C7 and C9 lights are for outdoor trees, yard and house decoration projects. They use a base socket that holds the lights, and they can withstand rain and other elements. If one bulb in a string of C7 or C9 lights burns out, the remaining bulbs will still burn. This feature is ideal when using the lights to outline your house, when you can't or don't want to remove the string of lights. But there are differences between C7 and C9 lights.
Bulb Size and Bases
C7 bulbs are smaller than C9 bulbs by 1 inch. C7 bulbs are 2 inches long and C9 bulbs are 3 inches long. C7 bulbs sit in a base known as a candelabra base and can only fit in this specific type of base. C9 bulbs sit in a base known as an intermediate base. C9 bulbs will only work in an intermediate base.
The two bulbs' electrical wattage is also different. C7 bulbs' wattage range from 2.5 watts to 7 watts and C9 wattage range from 3.5 watts to 7 watts. You cannot mixed the two bulb types in the same string and you cannot mix two C7 or C9 strings that contain two different wattages. Both cases will lead to the lights not illuminating and posing a possible fire hazard.
C9 lights shine brighter than C7 lights and are more visible than C7 lights. C9 bulbs are ideal for tall structures including two-story houses, barns and other tall buildings you are outlining. Colored C9 bulbs containing less color are also brighter than color C7 bulbs.