This is a Burke & James amberlight darkroom bulb, as is printed on its top (not very easily seen on this one). It is made of true amber (or brown if you prefer) glass, not painted, and uses a double-loop, single-anchored carbon filament. This bulb's light output is rated in candlepower, which is unusual for a bulb made in the 40's. Candlepower ratings fell out of widespread use with the advent of the tungsten filament in the 1910's, although some carbon bulbs continued to use them for a short time after that, but eventually shifting to watts. This bulb is rated at 16 candlepower, but smaller 8 candlepower versions were also made. Below is the description provided by the seller on the eBay auction listing:
Vintage Amber Darkroom Light Bulb (1940)
This is a vintage darkroom amber light bulb. My grandfather was a professional photographer many years ago. I acquired this light bulb after his passing in the early 1970's and put it aside. He had a habit of writing the date on everything he bought. The original box was dated 1940 (I forget the exact date, the original box fell apart and is no longer with it). It still has the printing on the top. It is marked: "Amberlight - Burke & James - 16 C.P. - U.S.A.". It is in perfect condition and the amazing thing is that it still works, emitting a wonderful glow.
And the following info was kindly provided by Tim, from Falls Church, VA:
"Burke & James is an camera and photographic supply company which shut down in the early 1980's. It is likely that Burke & James provided two different colors of darkroom bulbs: Amber and ruby, which are generally referred to as "safelights". These bulbs were made by somebody else and labeled with the Burke & James brand name. The light from these bulbs is very deeply colored and relatively dim. There were several companies that provided safelight bulbs, and one or two companies still do. The newer safelight bulbs are painted on the outside and the paint tends to scratch or flake off.
Certain black and white darkroom materials are insensitive to certain colors of light and could be handled using special illumination. Black and white printing paper can be handled using the light from an amber light bulb."
