GE F5000 DC Blacklight Glow Discharge
The GE F5000 lamp is intended to provide a small source of UV-A energy for the illumination of aircraft cockpits, whose instruments & panels were labelled with fluorescent paints. It was developed during WW2 to reduce light levels within the cockpit, so as to maintain improved night vision of the pilots while also making aircraft less visible to the enemy. These lamps produce a small amount of visible light in addition to the UV energy at 365nm, and to remove this it was customary to use them behind a Wood's glass filter.

The earliest applications employed small tubular fluorescent lamps, but these were not efficient owing to the relatively high electode losses, and complex control gear to convert the low voltage DC electrical supply of the aircraft to high voltage AC for running the lamps. Developments therefore focussed on miniature fluorescent lamps for use on a DC supply, and this style is believed to have originated from GE in 1941. It employs the then just-invented '360BL' cerium-acivated calcium phosphate UV-A emitting phosphor. It also marks the first use of the RP-12 bulb, having a slightly reflector-shape and in which the phospor coating is thicker on the sides than the flat face, to act as a reflector and direct a higher UV-A irradiance from the front of the lamp.

The lamp contains an incandescent filament with emitter coating which is momentarily preheated, to initiate a small glow discharge to the adjacent anode ring visble in the X-Ray image. It is ballasted by a current-limiting series resistance. To ensure correct polarity it employs an asymmetric bayonet cap, the anode being connected to the contact beside the etch, the cathode to the cap shell, and the momentary filament positive to the other cap contact.
Manufacturer: General Electric U.S.A.
Lamp Power: 4 Watts  
Lamp Voltage: 11 Volts  
Lamp Current: 0.35 Ampere  
Cap Type: BAY15d Brass + Vitrite
Bulb Type: RP-38 RP-12 in eighths/inch
Bulb Finish: Ca3(PO4)2:Ce3+ Soda-lime glass
Electrodes: Tungsten Coil cathode Metal ring anode
Electrode Gap: 10mm 0.394 inches
Atmosphere: Hg | NeAr
Luminous Flux & Efficacy: 45 lumens 11.25 lm/W
UV-A Irradiance: 9.5 mW/m² @ 1m from bulb crown
UV-A Flux: 285 fluorens (1 fl = 1 mW UV-A)
Colour Temperature & CRI: CCT: 24,000K CRI: Ra15
Chromaticity Co-ordinates: CCx: 0.235 CCy: 0.270
Rated Lifetime: 300 hours
Warm-up & Re-strike Time: 5 minutes Approx 5 seconds
Burning Position: Universal
Overall Length: 63 mm 21/2 inches
Factory: Youngstown, Ohio U.S.A.
Date of Manufacture: c. 1950 Date Code: 36Ō BL
Original Value: US $1.10 1953
References: 1) GE Large Lamp Catalogue, USA, 1953, pp.62-63
2) GE Large Lamp Price List, April 1953, p.14
3) GE Mercury Lamps - Operating Characteristics & Applications, C.E.Weitz & C.L.Amick, Form LS-103 February 1947, p.5
4) Fluorescent and Other Gaseous Discharge Lamps, W.E.Forsythe & E.Q.Adams, publ. Murray Hill 1948, pp.203-204
5) Lamps for a Brighter America, P.Keating, publ. McGraw-Hill Book Company USA, 1954, p.205
6) New Ultraviolet Phosphors, H.C.Froehlich, Trans. Electrochem. Soc V91, 1947, pp.241-263
7) US Patent 2,341,990, Electric Discharge Device, G.E.Inman, A.E.Lemmers, R.N.Thayer (General Electric), Filed April 1941
8) US Patent 2,206,567, Fluorescent Material and its Manufacture, W.A.Roberts, Filed September 1941
9) Black Light Aids Night Fighters, Popular Science, November 1942, pp.62-63
10) Evolution of Aircraft Cockpit Ultraviolet Lighting at website of AAFRadio.org U.S. Military Aircraft Avionics from 1939 to 1945
11) Aircraft Cockpit UV Instrument Light at website of Brooke Clarke's Electro-Optical Gadgets
12) U.S. War Department Technical Manual TM 1-406, Aircraft Electrical Systems February 1945, pp.124-125
13) Model 54 Transmission and Reflection Fluorimeter, E.E.Parshall & L.F. Rader, Geological Survey Bulletin 1036-4, 1957, pp.240-241
14) US Patent 2,324,384 Ultraviolet Screen for Fluorescent Lamps, W.G. Grimes, Filed June 1941
15) Photoelectric and Spectroradiometric Measurements @ 350mA.