Thorn 49-1101 - LED GaAsP Red

Thorn Lighting was one of the early pioneers of LED research and manufacturing. Its first products appeared in the 1972 catalogue and a large range quickly developed, but by the later 1970s these operations were abandoned. It soon became clear that the extremely low light output was not really compatible with the company's lighting business, and the much greater resources of the larger semiconductor companies were required to make significant improvements.

All Thorn LEDs are based on Gallium Arsenide Phosphide, the As:P ratio being adjusted to influence the colour of light from red through yellow to green. The base crystal is made of GaAs upon which an n-type GaAsP epitaxial layer of the desired As:P ratio is grown. Its surface is doped with zinc to form the p-type layer. Individual diodes are constructed by etching away part of the surface to leave an array of raised circular plateaus called mesas. Gold contacts are metallised across the back face of the array of diodes, and a small dot is deposited at the centre of each mesa. The crystal is finally sliced into multiple small dice. Each die is brazed onto a TO-18 transistor header, and a gold wirebond makes the connection from the top metallisation to the terminal post - note the crude early weld here. The whole is encapsulated in transparent epoxy to maximise light extraction and afford the necessary mechanical protection.

The mesa construction marks a considerable improvement over the ring-shaped metallisation on earlier devices such as Monsanto's MV-1. Energy in the older design was wasted by light emission even in the area under the metallisation, but with the mesa arrangement, the only light emission that is blocked is the tiny area under the gold wirebond.
Manufacturer: Thorn Lighting Ltd.
Lamp Voltage: 1.80 Volts
Lamp Current: 20 mA Nominal 40 mA Maximum
Lamp Power: 37 mW Nominal 74 mW Maximum
Cap Type: Insulated Au plated wires Ø 0.0175" x 0.1" Pitch
Bulb Type: TO-18 transistor
Bulb Finish: Red epoxy
Die Chemistry: GaAsP
Luminous Flux: 0.0015 lumens
Luminous Efficacy: 0.03 lm/W
Peak Intensity: 0.5 millicandela
Beam Distribution:
Peak Wavelength: 670 nm
Colour Temperature & CRI: CCT: N/A CRI: N/A
Chromaticity Co-ordinates: CCx: CCy:
Junction Temperature 100°C max.
Rated Lifetime: 100,000 hours
Overall Length: 19mm max.
Light Centre Length: 2.5mm
Factory: Leicester England
Date of Manufacture: Circa 1972-1975
Original / Present Value:
References: 1) Thorn Lighting Comprehensive Catalogue, UK, 1972/73, p.8:8
2) Thorn Lighting Comprehensive Catalogue, UK, 1973/74, p.8:14
3) Gallium Arsenide Phosphide Lamps, R. Hall, Thorn Lighting Journal No.8 pp.6-8, Spring 1972