Question about C7-1/2 Light Bulbs

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I recently had a question from a potential buyer about C7-1/2 light bulbs. She wanted to know the difference between a C7 and a C7-1/2 bulb

So, not being able to find this particular answer in my search of the web, here’s what I think.

  • It does not refer to the Base Size. The part that screws into the socket comes in three sizes: miniature, candelabra and intermediate. Most C7 Christmas lamps use a candelabra base. I’ve never seen any difference between the base size of C7 and C7-1/2 lamps.
  • It does not refer to the Shape of Glass. The C part of the description describes the shape of the glass envelope. C= conical, G= globe or globular, T= tubular. So the shape of the glass is the same, Conical.
  • I think that it refers to the Envelope or Glass Size. Standard sizes are as follows:
    • Size 6=6/8″ wide
    • Size 7= 7/8″ wide
    • Size 9= 9/8″ wide

    I think that the envelope size for a 7-1/2 bulb is slightly larger than 7/8 inches wide, most likely 15/16 inches wide. But I haven’t measured to be sure.

Anyone have better information?

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2 Responses to Question about C7-1/2 Light Bulbs

  1. David Smith says:

    It refers to the wattage of the lamp. The original C7 1/2 lamp was 7 1/2 watts. The bulb was reduced to 7 watts and called C7. Current C7 candelabra base Christmas lamps have been reduced to 4 or 5 watts. The no longer produced C6 lamp produced 6 watts and the large C9 1/2 outdoor intermediate base lamp produced 9 watts. Current intermediate base lamps are called C9 lamps and produce 7 watts. The older lamps got really hot and were a major fire hazard. I don’t know if the wattage was reduced due to legal requirements or to reduce power consumption.

  2. mee says:

    7 1/2 is the enery used (Watts).

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