Topic summary
Light bulb
Extracted from the Wikipedia article Electric light.
Form factor
Many lamp units, or light bulbs, are specified in standardized shape codes and socket names. Incandescent bulbs and their retrofit replacements are often specified as "A19/A60 E26/E27", a common size for those kinds of light bulbs. In this example, the "A" parameters describe the bulb size and shape within the A-series light bulb while the "E" parameters describe the Edison screw base size and thread characteristics.