Because there are variety of types of bulbs, different codes are given to them to tell which is which. C7 and C9 string lights are for outdoor trees, yard and house decoration projects. 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 light. These features make C7 and C9 very popular, especially in American market. But what’s the difference between C7 and C9 lights?

The first difference comes on the shape. C7 bulbs are short than C9 bulbs by 1 inch. C7 bulbs are 2 inches long and C9 bulbs are 3 inches long. So C7 looks short and fat, and C9 looks tall and thin.

Beside the shape，bases of C7 and C9 were also different. C7 bulbs sit in a base known as a candelabra base, and C9 bulbs sit in a base know as an intermediate base. We also have codes for bases, for C7 lights, the base is E12, and for C9 lights, it is E17.

When C7 and C9 are both osram lamp, because of their size are different, both the power consumption and illumination are different. But when LED comes into being, more and more factories start make C7 and C9 with LED bulbs, so the difference on power consumption and brightness is not big now, but difference on shape is still a way to tell which is C7 and which is C9.