Osram Miniature UV-A Source HgN 13W

During WW2 there was a heightened requirement for small sources of UV-A energy for operation on low voltage DC power supplies, for illumination of vehicle interiors - in particular for aircraft cockpits but also for train and truck dashboards. Until then it had been standard practice to employ miniature incandescent lamps, and this called for large numbers of lamps with complex illumination systems. It was also difficult to uniformly light large surfaces, with the result that some areas appeared brighter than others.

Parallel developments in fluorescent lighting at that time were resulting in new luminescent materials, and by painting these onto control panels the phosphors could be illuminated uniformly by floodlighting the area with invisible UV-A radiation. Another advantage of this approach was that the total light level was greatly reduced, making such vehicles less obvious to enemy aircraft.

One of Osram's first lamps was this HgN 13W (HgN = Quecksilber Niederdruck, Low Pressure Mercury), conceived by Dr. Ernst Summerer and Dr. Hans Ewest, and intended to be operated behind a violet glass filter. The short discharge gap of just 30mm has a potential of only 13-15V, and as such can be ballasted by an ohmic resistance in series with the 24V supply of commercial vehicles. The anode is a metal ring at the far end of the bulb, and the cathode is a tungsten coil enclosed within a small ceramic cylinder, which is momentarily preheated to strike the discharge. A starting electrode located just infront of the anode is connected to the cathode via a resistor sealed into a glass tube. The bulb is pinch-sealed at one end, and is equipped with a 3-pin bayonet cap to ensure correct polarity of the DC supply.
Manufacturer: Osram KG
Lamp Power: 13-15 Watts  
Lamp Voltage: 13-15 Volts  
Lamp Current: 1 Ampere  
Cap Type: B22d-3 Brass + Vitrite
Bulb Type: T-22 T-7 in eighths/inch
Bulb Finish: Clear Glass UV-A transmitting
Electrodes: Tungsten Coil cathode Metal ring anode
Electrode Gap: 30mm 1.18 inches
Atmosphere: Hg | Ar
Luminous Flux: 35 lm
Luminous Efficacy: 2 lm/W
UV-A Irradiance: 2.5 mW/m² @ 1m distance
Colour Temperature & CRI: CCT: 11,500K CRI: Ra7
Chromaticity Co-ordinates: CCx: 0.250 CCy: 0.320
Rated Lifetime: Unknown
Warm-up & Re-strike Time: 1 minute Instantaneous
Burning Position: Universal
Overall Length: 80 mm 31/8 inches
Factory: Werk-S Charlottenburg Berlin, Germany
Date of Manufacture: 1950 September? Date Code: p30 A6776
Original Value: Unknown
References: 1) Eine Lampe zur Fluoreszenzanregung für Sonderzwecke, E.Summerer, Technisch-Wissenschaftliche Abhandlungen der Osram-Gesellschaft, 1943 p66.
2) Instruction and wiring sheet supplied with lamp.