This article is about the older Christmas light bulbs and not about the miniature lights of today.
That being said, you may have noticed that there is a confusing array of terms used to describe the sizes of vintage Christmas light bulbs. So here’s a quick guide to some of the terms used
- Base Size: the part that screws into the socket comes in three sizes: miniature, candelabra and intermediate. However, most of us commonly refer to these as C6, C7 and C9.
- Envelope or Glass Size: Size 6=6/8″ wide, Size 7= 7/8″ wide, 9= 9/8″ wide
- Shape of Glass: Describes the shape of the glass envelope. C= conical, G= globe or globular, T= tubular
So this means that a C6 light would have a cone shape, be 6/8″ wide and have a miniature base. A C7 light would have a cone shape, be 7/8 inches wide and have a candelabra base. A C9 light would have a cone shape, be 9/8″ wide and have an intermediate size base.
There’s nothing more frustrating than ordering a replacement lamp that is the wrong size. Hopefully the sizes and measurements here will help you sort out the seller’s descriptions. If it’s not clear, ask before bidding or buying.
I’m endebted to The Antique Christmas Light Site for their clear and accurate information. I treat them as an authority in the area. You should too.