The microwave sulpkur lamp was invented in 1990 by US scientist Michael Ury, at the end of a 4-year research period. Subsequently, in 1992, Fusion Lighting Inc, Maryland (USA) obtained all rights for the development of the light source, making it available commercially as the Fusion Light Drive 1000.

These sulphur lamps frequently use hollow light guides to distribute and transport the light, with 3M’s Light Pipe being a popular choice. We’ll talk more about light guides later on in this article.

Lamp development

The sulphur lamp bulb consists of a 35mm quartz sphere filled with a few milligrams of yellow sulphur powder and an inert gas (such as argon) which is weakly ionised using microwaves. When it is ionised, the argon heats the sulphur into a gaseous state, thereby forming diatomic sulphur molecules or "dimers". These dimers emit a broad continuum of energy as they drop back to lower energy states.

The light radiation that is produced is almost entirely within the visible spectrum, with very little undesirable ultraviolet or infrared radiation.

The microwaves are generated by two magnetrons operating at a frequency of 2.45GHz. As it is irradiated, the lamp bulb is spun at 3400 rpm (apparently to stabilise the plasma’s position within the bulb), with two fans providing forced air cooling. Fig.1 shows a schematic diagram of the lamp while Fig.2 is a more detailed view of the Fusion Light Drive 1000.

Note that the sulphur bulb is installed in the optical centre of a reflector system, to direct the light output.