What is a type A19 light bulb?

The A19 light bulb is the most common shape of incandescent bulb, according to EagleLight. The A designation refers to the standard light bulb shape, and the 19 refers to the diameter of the bulb in eighths of an inch, indicating a diameter of 2 3/8 inches.

The Energy Independence and Security Act of 2007 brought the production of many standard A-style bulbs to an end as of December 2014 and calls for the use of more energy-efficient options in most applications. According to Bulbs.com, the act allows 22 types of exceptions for the older, Edison-type bulbs; however, the act encourages consumers to replace most of these bulbs for higher efficiency.