L/11 Bunch Filament Lighthouse Lamp
Illustrated here is a typical medium 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/11, also known under its fuller reference BSL11 according to British Standard 1546, and sometimes referenced under the Trinity House Engineering Chief's nomenclature EC105.

It is designed for 100V 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 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.

The filament assembly is mounted on a conventional hard glass stem, whose external leadwires are sheathed in Vidaflex sleeving to prevent accidental contact due to the variations inherent with the fully hand-made construction. It is sealed into a spherical bulb blown in borosilicate glass to withstand the high thermal loading. The cap is of the standard P40s mogul prefocus type, individually aligned to the filament centre to avoid need for refocussing the optical assembly after replacing the lamp.
Manufacturer: Victory Lighting Type L/11 (EC105)
Lamp Power: 1000 Watts
Lamp Voltage: 100 Volts
Lamp Current: 10.0 Amperes
Cap Type: P40s/45 Ni plated brass & Porcelain
Bulb Type: G-130 G-41 in eighths/inch
Bulb Finish: Clear Borosilicate glass
Filament Type: C-5 Bunch
Filament Size: 15mm x 20mm
Atmosphere: Argon-Nitrogen Red phosphorus getter
Luminous Flux: 18,000 Lumens
Luminous Efficacy: 18.0 Lumens per Watt
Luminance: 600 cd/cm²
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: 195 mm 711/16 inches
Light Centre Length: 80±3 mm 33/16 inches
Factory: Wembley England
Date of Manufacture: July 2001 Date Code: JG
Original Value: `
References: 1) BS 1546 - British Standard Specification for Electric Lamps for Lighthouses, 1963.
2) Lighting Industry Federation Schedule of Projection Lamp Types, London, 1982.
3) Trinity House Engineering Chief's Specification of Electric Lamps for Stores Supplies, 1962/63.