Cockpit Light AN3038-2A

Here is a WWII-era Cockpit Light AN3038-2A, made by Grimes, part number B4821 as used in aircraft of the US Army Air Force and US Navy. This light is designed to hold an ultraviolet fluorescent lamp (not included), to illuminate instruments and panel markings for legibility under low ambient lighting conditions. 

The lens appears black, but we are assuming that with the bulb installed and illuminated, the ultraviolet light wavelength should penetrate. When a normal incandescent bulb is placed behind the lens, red light can be seen through the lens. 

The lens cover can be removed and retained by a chain, see photos. The lamp is affixed to a mounting bracket.

The lamp measures ~1.5 inches diameter and ~3 inches long, and is in reasonable condition given its age.