EC102 Cruciform Filament Lighthouse Lamp

Illustrated here is a typical high power lamp formerly used in English and Welsh lighthouses operated by Trinity House Corporation, and Scottish lighthouses of the Northern Lighthouse Board. Its is classified by Trinity House as lamp type EC102 (Engineering Chief's codes), and is very similar to the British Standard BS1546 type L/18 but 4000W and 18lm/W instead of 4500W 17.5lm/W.

It is designed for 80V circuits, a low voltage which used to be provided by diesel generators or batteries prior to the extension of the mains electricity grid to the remote and offshore locations of British lighthouses. The filament has the classical cruciform shape originally developed by Philips, which consists of two interlocking grid-shaped filaments arranged in an X-configuration. This elegant construction helps to ensure that the lighthouse appears equally bright from all viewing angles at sea level. The light signal from such lamps used to be coded into brief pulses of precise and repetitive duration to aid identification, by a system of optical lenses rotating around the lamp, and spatial variations in luminous intensity from the filament may present an incorrect signal.

The filament assembly is mounted on a massive soft glass stem having four seals to heavy-guage dumet wire, and laterally tubulated to the exhaust tube via the old-fashioned Jaeger technique. This is conventionally sealed into a huge spherical soft glass bulb. The cap is of the standard E40 GES Goliath Edison Screw pattern, hand-turned in heavy gauge copper, and lacks the later pre-focussing collars that were added to avoid the need for manual re-alignment in the optical system after each lamp change.
Manufacturer: Siemens Brothers Type EC102
Lamp Power: 4000 Watts
Lamp Voltage: 80 Volts
Lamp Current: 50 Amperes
Cap Type: E40s/82x82 Copper & porcelain
Bulb Type: GS-295 GS-93 in eighths/inch
Bulb Finish: Clear Soda-lime silicate glass
Filament Type: 2C-13X Cruciform
Filament Size: 26mmx42mm
Atmosphere: Argon-Nitrogen Red phosphorus getter
Luminous Flux: 72,000 Lumens
Luminous Efficacy: 18.0 Lumens per Watt
Luminance:
Colour Temperature & CRI: CCT: 3000 Kelvin CRI: Ra 100
Chromaticity Co-ordinates: CCx: 0.452 CCy: 0.409
Rated Lifetime: 800 hours
Burning Position: Vertical cap down ± 30°
Overall Length: 535±15 mm 21 inches
Light Centre Length: 260±3 mm 101/4 inches
Factory: Strand Road, Preston UK
Date of Manufacture: January 1948 Date Code: 25
Original / Present Value: Unknown Unknown
 
References: 1) United Kingdom Ministry of Defence Directorate of Standardisation, DefStan 62-6, Nato Stock Nr. 996-7835
2) AEI Mazda Manufacturing Specification for Lamp 85-6901.