N’ key physical differences between C7 and C9 bulbs
There are 5 key physical differences between C7 and C9 lights:
- Size – C9 lights are larger by about ¾” in length and are typically wider.
- Light Output – C9 lights tend to produce greater amounts of light
- Energy Consumption – C9 bulbs typically consume more electricity than C7 bulbs
C9 vs. C7 size
C9 bulbs are typically 2 ¼” in length, with varying widths depending on the manufacturer. C7 bulbs are typically 1 ½” in length, again with varying widths depending on the manufacturer.
Bear in mind that the C7 and C9 designations do not require the bulbs to be a specific length or width. The above is stated as what is typical.
What does the ‘C’ stand for?
The ‘C’ in C6, C7, and C9 stands for ‘Candle’, ‘Cone’, or ‘Christmas’. The definition has changed throughout the last 100 years and varied based on the manufacturer.
General Electric originally sold their lights with the ‘C’ standing for ‘Cone’ and then, later changing that designation in 1972 to ‘Christmas’. Other manufacturers have used ‘C’ to designated the design, hence ‘Candle’ and the candle shape of the bulb.
What does the 7 or 9 stand for in C7 or C9?
The number indicates the base size of the bulb, which is the most important point to know.
A C7 bulb has an E12 candelabra base and a C9 bulb has an E17 intermediate base. The numbers in each of those bases sizes, E12 and E17 relate to the diameter of each base in millimeters. Therefore, an E12 base is 12mm (0.472 inches) in diameter and an E17 is 17mm (0.669 inches) in diameter.
As a point of reference, the standard light bulb in your home is an E26.
C9 vs. C7 light output
C9 bulbs generally produce greater amounts of light than their C7 counterparts. However, this will vary greatly across different brands, models, and manufacturers. These are the other factors to consider:
- Incandescent vs. LED
- Physical size of the bulb’s glass or polycarbonate case
- Type of glass or polycarbonate – faceted, smooth, opaque, etc.
Below is a table of the output of light in lumens of a few different bulbs tested.
C9 vs. C7 Energy Consumption
C9 bulbs will generally consume more electricity than C7 bulbs; however, the exception to this is with LEDs.
Manufacturers will often use the same LED(s) in a C7 and C9 bulb and simply adjust the shell. There’s nothing wrong with this, as LEDs are incredibly bright, regardless of their quantity or size – the difference would be negligible.
LED bulbs consume well under a watt of electricity per bulb as it stands (most being around 0.8 watt). Incandescent bulbs consume significantly more at around 5 to 8 watts.
With an incandescent bulb, the energy consumption is a factor as, for example, a C7 bulb may consume 5 watts of electricity, while a C9 may consume 7 or 8.