EC111 Rapid Nigrescence Lighthouse Lamp

The EC111 lighthouse lamp was developed by Osram-GEC for Trinity House Corporation of Great Britain. It is unusual in its electrical rating, optical configuration of the filaments, and its mode of operation. Earlier British lamps had low voltages of 50-100V, because they were operated from batteries or diesel generators in remote places beyond the reach of the electricity grid. The higher power lamps had one or two filaments, and their light output was coded with massive rotating optical systems. By the 1960s mains supplies had reached the larger lighthouses and a 240V lamp became feasible - and efforts were made to pulse the light signal electrically.

The first lamp for this purpose was the 240V 3000W EC111 developed by Osram-GEC. It employs six small 500W filaments, each arranged in pairs to form a triple cylindrical arrangement. The low thermal mass of these small filaments reduces the nigrescence time as they cool after switching off, to achieve more precisely defined light pulses.

The lamp is hand-made throughout and has a ferociously complex construction. Each pair of filaments is mounted on its own stem assembly, these three glass tubes being fused to a larger glass stem having a concentric exhaust tube, which is then sealed to the bulb neck. The filaments are supported on fine molybdenum wires held in ceramic rings. The bulb is mouth-blown in soda-lime glass by the Osram Lemington glassworks, and the cap hand-turned from solid copper by Lamp Caps of Chesterfield. The EC111 lamp was both expensive to produce and very fragile, and around 1975/76 it was superseded by the rather simpler EC111A lamp designed by Thorn Lighting.
Manufacturer: Osram-GEC Type EC111
Lamp Power: 3000 Watts
Lamp Voltage: 240 Volts
Lamp Current: 12.5 Amperes
Cap Type: P89s/82x75 Solid Copper & Porcelain
Bulb Type: GS-240 GS-75.5 in eighths/inch
Bulb Finish: Clear Soda-lime silicate glass
Filament Type: 6C-15 Triple Cylindrical
Filament Size: 16mm x 50mm
Atmosphere: Argon-Nitrogen Red phosphorus getter
Luminous Flux: 43,500 Lumens
Luminous Efficacy: 14.5 Lumens per Watt
Luminance: N/A
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: 435 mm 171/8 inches
Light Centre Length: 235±3 mm 91/4 inches
Factory: Wembley England
Date of Manufacture: March 1969 Date Code: 35
Original Value: GB£23.45 (1974)
References: 1) Osram-GEC Lamp Catalogue, 1975
2) Trinity House Engineering Chief's Specification of Electric Lamps for Stores Supplies, 1962/63.
3) Lighting Industry Federation Schedule of Projection Lamp Types, London, 1982.
4) Twenty Years in Lighthouses 1924-1944, F.W. Cooper, Lighthouse Department, Chance Brothers Limited, 1979, pp.19-20.
5) Private Communication, Ian Tutt, Trinity House Lighthouse Corporation Ltd, Cowes, Isle of Wight, August 1995.
6) Private Communication, Bill Bellion, Watermarks Ltd., Hayling Island, September 1995.
7) Private Communication, Graham Skeldon, Osram Wembley, 1995.