Light Bulb Series Encoding

I needed to replace an “A19” light bulb. What does “A19” mean?

The “A” describes the shape of the bulb; in this case, the standard household-shaped bulb (💡).

“19” is more tricky. It’s the diameter of the bulb in 1/8ths of an inch, so my bulb is 19 times 1/8th of an inch, or 2 3/8 inches. Countries on the metric system call these “A60” for 60 millimeters, which is… better!

Everything is encoded! Signifiers like “BR30” (“Bulged Reflector”, 3.74inches x 8 ≈ “30”) are never random.