Lamp Guide: General Information Posted on February 16, 2017February 16, 2017 by Brandy McNeil Maximum Overall Length (in inches)- includes the sockets for incandescent bulbs and pins for fluorescent bulbs (MOL). Lamp Diameter – Lamp diameter is expressed in eighths of an inch (1/8″). For example: an A21 bulb is 21 – eighths of an inch or 2 5/8″ in diameter at it’s maximum dimension (DIA). Beam Spread Legend- (NSP – NARROW SPOT) (SP – SPOT) (NFL – NARROW FLOOD) (FL – FLOOD) Incandescent HID Compact Fluorescent Fluorescent DIAMOL DIA MOL MOL Nominal Length is the dimension from back of socket to back of socket Post navigation UL Fuse ClassificationLamp Guide: Fluorescent