L/9 Bunch Filament Lighthouse Lamp

Illustrated here is an early form of low 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 the Lighting Industry Federation as type L/9, also known under its fuller reference BSL9 according to British Standard 1546, and sometimes referenced under the Trinity House Engineering Chief's nomenclature EC114.

It is designed for operation directly on the 240V mains supply, which indicates that it would have been used for a land-based lighthouse close to areas of civilisation, because most British lighthouses at this time were in remote locations and employed low voltage lamps driven from batteries or diesel generators.

This particular model is in fact a slight modification of the type B1/3 floodlighting lamp. Such lamps were normally equipped with an E40 GES Goliath Edison Screw cap, however for lighthouse service the filament had to be better aligned, and the L/9 lamps therefore make use of a P40 pre-focus cap. This avoids loss of time in re-focussing the optical system after replacing a failed lamp. The filament construction is the standard bunch design employed in Class B1 floodlighting lamps, having a semi-cylindrical shape. One drawback of this for lighthouses is the non-uniform luminous intensity distribution around the lamp axis, which may cause variations in the apparent brightness of the signal from different directions. Although this was tolerable for the lower wattage lamps having limited signalling range, higher power lamps such as the L/25 tended to make use of a double filament having a full cylindrical shape.
Manufacturer: Osram-GEC Type L/9 (EC114)
Lamp Power: 500 Watts
Lamp Voltage: 240 Volts
Lamp Current: 2.08 Amperes
Cap Type: P40s/45 Brass & Porcelain
Bulb Type: G-130 G-41 in eighths/inch
Bulb Finish: Clear Soda-lime silicate glass
Filament Type: C-5 Bunch
Filament Size: 13mm x 17mm
Atmosphere: Argon-Nitrogen Red phosphorus getter
Luminous Flux: 7,250 Lumens
Luminous Efficacy: 14.5 Lumens per Watt
Luminance: 300 cd/cm²
Colour Temperature & CRI: CCT: 2900 Kelvin CRI: Ra 100
Chromaticity Co-ordinates: CCx: 0.444 CCy: 0.406
Rated Lifetime: 800 hours
Burning Position: Vertical cap down ± 30°
Overall Length: 195 mm 711/16 inches
Light Centre Length: 80±3 mm 33/16 inches
Factory: Hammersmith England
Date of Manufacture: March 1956 Date Code: 75
Original Value:
 
References: 1) Osram-GEC Lamp Catalogue, 1975
2) BS 1546 - British Standard Specification for Electric Lamps for Lighthouses, 1963.
3) Lighting Industry Federation Schedule of Projection Lamp Types, London, 1982.
4) Trinity House Engineering Chief's Specification of Electric Lamps for Stores Supplies, 1962/63.