C9 lights are large, traditional lights that are used outdoors.  When people speak of traditional Christmas lights, they can be referring to either the C7 (indoor) lights or the very large C9 (outdoor) lights.  C9 lights are heavy-duty, weather resistant and designed for outdoor use.  A C9 bulb is 2.5 inches tall and has an elongated egg shape.  Contrary to popular myth, they are still easily available.  They can be bought at large chain department stores, on the Internet or on eBay.

It is easy to confuse the C9 lights C7 lights and vice-versa.  However, there are some major differences between them and they are not interchangeable.  The biggest difference is the size.  The C9 light is bigger than the C7 light and it requires a bigger socket than the C7.  In addition, the C9 light is designed for outdoor use; the C7 light is designed for indoor use.  Below, I have included a picture of a C9 light and a C7 light to illustrate their differences.     

History

C9 lights were first introduced in 1927 by General Electric.  They were designed for outdoor use and GE and other Christmas light manufacturers sponsored neighborhood "decorating with colored light" contests, in an effort to boost sales.  Early versions of the C9 light had a swirl pattern, which was later retired in favor of a smooth look.  C9 light sets used the parallel circuit, which meant that if one light went out, the others stayed lit.  After World War II, C9 lights became extremely popular for outdoor use. 

Some interesting facts

C9 lights can still be purchased today.  The best places to go to buy C9 lights are large chain department stores, the Internet and eBay.  They are available as clear or colored bulbs or as opaque or transparent.  The technical term for opaque lights is ceramic.  The technical term for the see-through lights is transparent.  Below, I have included pictures of ceramic and transparent C9 lights. 

Ceramic                                                        Transparent

I always recommend using ceramic bulbs, because they give off a warm, soft and cheerful glow and not the harsh glare of the filament.  Transparent lights are hard on the eyes.  Whatever you do, don't mix ceramic lights with transparent lights.  Together, they look as good as a tuxedo with tennis shoes. 

I always recommend using mulitcolored sets of lights.  Using lots of different colors makes your tree, bush or outdoor display look bright, cheerful and festive.  Using all white or clear bulbs creates a washed-out look.  With lots of colors, you can't go wrong and they'll add greatly to whatever other outdoor displays you use. 

Some other interesting facts

• C9 lights use parallel circuits.  That means that if one light goes out, the others stay lit.  No more searching for the burnt-out bulb. 
• C9 lights are long-lasting.  You can easily get a good five years out of a string of C9 lights.  With the C9 lights, you won't have to buy new lights every year.  In the long run, that saves you money.   
• C9 lights burn at 7 watts each.
• C9 lights are easy to see from outside.  A tree, bush or holiday display that uses C9 lights is very visible and visible from a great distance.  Used outside, the little twinkle lights are barely visible.
• The sockets of C9 lights have molded clips.  You can clip the sockets on to your tree or bush's branches and they'll stay put, unlike the little lights, which slide around. 

Some outside applications

C9 lights can be used in a number of ways outside.  Your only limit is your imagination.  The most common ways that C9 lights are used outside is on trees and bushes and around buildings.  You can decorate your front bushes or trees with C9 lights or put them around your front door or your front porch.  If you plan to put lights around your front door, you should use a dark green garland as a backdrop.  A string of lights by themselves look forlorn.

In addition, C9 lights can be used to decorate a tree that is fifteen feet tall or higher.  They are great if you have a very large tree to decorate--inside or out. 

Bush

A typical C9 light set

Your standard C9 light set comes with twenty-five bulbs.  The usual length is twenty-five feet, with twelve-inch spacing between sockets.  The light set can be connected to another light set; you can connect up to two strings of C9 lights.  The color of the cord and sockets is usually green.  On a multicolored set, the bulbs are usually available in the colors of red, blue, white, orange and green. 

One color that you would expect to find, but never do is yellow.

Yellow C9 lights are very hard to find.  They can not be found at any stores in the U.S., yet a tree without yellow lights is like a sandwich without bread.  Below, I have included a drawing of two bushes, one with and one without yellow lights.  See the difference!

Without yellow lights                                   With yellow lights

Fortunately, it is possible to buy yellow ceramic C9 lights on the Internet and on eBay.  As eBay's advertising slogan goes, 'Whatever IT is, you can find IT on eBay.'  That goes for yellow C9 lights.  Yellow C9 bulbs can easily be added to existing sets and will complete the color spectrum. 

Lighting tips

To figure out how many C9 lights you'll need for your tree or bush, multiply length X width X 2. 

When buying C9 lights for your outdoor decorating, always buy more sets than you think you'll need.  You may end up needing more sets than you had intially thought and though C9 lights are heavy-duty, you can count on at least one light burning out during the holidays.  If you have an extra set, you'll have a ready source of replacement lights.  In the unlikely event that a string should short out, you can quickly replace it with that extra set you bought. 

C9 lights are not cool burning, so they should not be used for indoor displays.  They are designed for outdoor use only.  They are not cool burning and pose more of a fire hazard than the slightly smaller C7 lights, which are designed for indoor use.

In conclusion

I hope this guide has been helpful and that it has given you some fresh ideas about how to decorate for Christmas or the holidays.  With the C9 lights, you should have an easy time making your house stand out and be the talk of the neighborhood.