Mazda Bayonet Capped Silicate Fluorescent
The first hot-cathode fluorescent lamp produced in Britain was a 3ft 30W rating, introduced in 1938 by the inventor of that technology, Osram-GEC. It was a crude article with poor efficacy and cable connectors, much less refined than the 4ft 40W tube that GE of America introduced in the same year, based on the original GEC work. Both lamps employed a mixture of phosphors to create a white light, these being pink zinc-beryllium silicate plus blue magnesium tungstate.

Owing to the outbreak of war, production of the GEC lamp was suspended because it would have been intolerable to introduce this completely new concept, which required a new electrical ballast and new end caps. The British lamp was quickly re-designed around materials that were readily available. The smallast ballast then in use was intended for 80W high pressure mercury lamps - the length of the tube was therefore increased to what has since become the standard British size of 5 feet. Lamp caps were taken from ordinary incandescent lamps, resulting in the most unusual and exclusively British design of this 5ft bayonet-capped tube. Later an 8ft BC tube was introduced to operate on 125W high pressure mercury ballasts. The high electrical loading of these tubes made them somewhat inefficient though, and after the war when effort could be devoted to creating new ballasts, they were adjusted to 65W and 85W, and adopted the American-style bi-pin end caps.

The design was quickly copied by the GEC's competitors, of which this is a typical example. This particular lamp is notable for its great weight, some three times that of a modern 5' tube. This is owing to the glass tube having been drawn by hand with much greater wall thickness than usual.
Manufacturer: The British Thomson-Houston Co. Ltd.
Lamp Power: 80 Watts
Lamp Current: 0.87 Amps
Lamp Voltage: 100 Volts
Cap Type: B22d/25x26 Brass + Vitrite
Bulb Type: T-38 T-12 in eighths/inch
Bulb Finish: Warm White (ZnBe)2SiO4:Mn and MgWO4
Electrodes: Coiled-Coil + Anode Plates Triple Carbonate emitter
Discharge Length:
Atmosphere: Hg | Ar
Luminous Flux: 2,800 (initial) 1,920 (average)
Luminous Efficacy: 35 lm/W (initial)
Colour Temperature & CRI: CCT: ~3000K CRI: ~Ra 50
Chromaticity Co-ordinates: CCx: CCy:
Rated Lifetime:
Warm-up & Re-strike Time: 1 minute Instant
Burning Position: Universal
Nominal Length: 1527 mm 60 inches
Factory: Rugby England
Date of Manufacture: January 1945 Date Code: B0137
Original Value: £1 4s 0d (1947)
 
References: 1) BTH-Mazda Lamp Catalogue, UK, 1947
2) Metrovick Lamp Catalogue, UK, 1947
3) Thorn Lighting Comprehensive Catalogue, UK, 1969
4) The GEC Research Laboratories 1919-1984, R.Clayton & J.Algar, publ. Peter Pereginus 1989, ISBN 0 86341 146 0, pp.79-80 & 87-92
5) Lamp Phosphors, H.L.Burrus, publ. Mills & Boon 1972, ISBN 0 263 05133 1, pp.9-13