Mazda SL/H Dimmable Low Pressure Sodium
Manufactured using the same discharge tube design as the equivalent SLI 60W lamp, this is a very special dimmable version which was hand made in only very small quantities.  Produced in 60W and 200W ratings, the application of this lamp was as a dimmable light source for airfield installations where large arrays would be installed leading up to the runway.

The luminous flux of this lamp could be varied to suit the prevailing weather conditions, and low pressure sodium light was preferred for this application because of its monochromatic output near to the peak sensitivity of the human eye which ensures maximum visibility and minimal light scattering by fog and mist.

Low pressure sodium lamps can be dimmed easily, however beyond a certain point the wall temperature of the discharge tube falls to a level where there is insufficient sodium vapour in the discharge tube for efficient light generation.  For peak efficacy it is necessary to maintain the wall temperature at around 260 degrees celsius, and usually thermal insulation means would be designed to attain this value with the lamp operating at full power.  For a dimmable lamp a variable degree of thermal insulation is called for, in order to maintain sufficient sodium vapour at various operating levels.

This lamp makes use of a nichrome heater coil wound around a mica-clad glass sleeve surrounding the discharge tube.  As the lamp is dimmed, current through the heater must be increased to keep the discharge tube at full temperature.  The contacts are binding posts attached to a Sindanyo base.
Manufacturer: Associated Electrical Industries Ltd.
Lamp Power: 60 Watts
Lamp Current: 0.83 Amps
Lamp Voltage: 80 Volts
Cap Type: Triple Binding Post Sindanyo Insulator
Bulb Finish: Clear Soda-lime glass
Bulb Type: Inner: TD-16 Outer: T-38
Overall Length: 427 mm 16¾ inches
Light Centre Length: N/A
Arc Length:
Electrodes: CCC-6 Black Tungsten BCT emitter
Atmosphere: Na | 98.5% Ne, 1.5% Ar Outer: Vacuum
Luminous Flux: Dimmable
Luminous Efficacy: Variable
Colour Temperature & CRI: CCT: 1700K CRI: Ra-44
Chromaticity Co-ordinates: CCx: 0.574 CCy: 0.425
Burning Position: Horizontal ± 5°
Rated Lifetime: Not Published
Warm-up & Re-strike Time: 12 minutes Instantaneous
Factory: Leicester England
Date of Manufacture: Circa 1960
Original & Present Value: Unknown