Mazda Dimmable Linear Low Pressure Sodium
Following the introduction of AEI's Linear Sodium lamp, it was quick to find an application in airfield lighting. The combination of high output and narrow diameter made it eminently suited to use in a parabolic mirror to produce a narrow beam of high intensity in runway approach lights, and the monochromatic yellow output was highly effective in penetrating rain and fog compared to other light sources. Rather inconveniently though it could not be used at night time because it caused too much glare to pilots, and LPS lamps cannot realistically be dimmed because the sodium vapour begins to condense out of the discharge.

This lamp was created to solve that problem, and allows the sodium lamp to be dimmed to suit the prevailing weather conditions and daylight level. A dimmable low pressure sodium lamp requires a varying level of thermal insulation, and that is provided here by a heater coil of nichrome resistance wire wound around a glass sleeve surrounding the discharge tube. The spacing between the turns must be kept constant so as to maintain a flat thermal profile along the lamp length, and this is ingeniously ensured by sandwiching a sheet of mica between the wire and the glass tube. The mica, originally a flat sheet, is held in its circular shape under compression of the resistance wire and as the wire elongates when heated up, the mica maintains enough force on the wire to prevent changes in the pitch of its coils.

The discharge tube is the same as that employed in the standard 60W general lighting lamp. End caps are machined from BTH's Sindanyo asbestos-substitute, and brass binding posts are used for the electrical terminals. These special Airfield lamps were made in both 60W and 200W ratings.
Manufacturer: Associated Electrical Industries
Lamp Power: 60 Watts
Lamp Current: 0.83 Amps
Lamp Voltage: 80 Volts
Cap Type: Triple Binding Post BTH Sindanyo Insulator
Bulb Type: T-38 T-12 in eighths/inch
Bulb Finish: Clear Soda-lime glass
Electrodes: CC-6 Black W + BCT emitter
Arc Length: 290 mm 117/16 inches
Atmosphere: Na | 99%Ne 1%Ar Outer: Hard Vacuum
Luminous Flux: 6,000 lm (@ 100 hrs)
Luminous Efficacy: 95 lm/W (@ 100 hrs)
Colour Temperature & CRI: CCT: 1700K CRI: Ra -44
Chromaticity Co-ordinates: CCx: 0.574 CCy: 0.425
Rated Lifetime: 6,000 hours 70% survival, 100% flux
Warm-up & Re-strike time: Approx. 15 minutes Instantaneous
Burning Position: Horizontal ± 20°
Overall Length:
Insertion Length: N/A
Factory: Leicester England
Date of Manufacture: Circa 1960
Original & Present Value: Unknown
 
References: 1) Patent GB 955,655, Improvements Relating to Discharge Lamps, AEI Lamp & Lighting Co. Ltd., Filed May 1959.