||Although Crompton is traditionally thought of as an incandescent lamp manufacturer, the company was quite innovative in both mercury and fluorescent lamp manufacture in the 1950's and 1960's.
Crompton's MA lamp was technologically unique and it survived in the fiercely competitive mercury lamp business by patenting its novel lamp construction technique. MA arc tubes do not require thermal insulation as do sodium lamps, all that is required is a stationary layer of gas since draughts can cause variations in light output by affecting the arc tube temperature. Whereas competitors went to the expense of sealing arc tubes into an outer bulb filled with carbon dioxide or nitrogen gas, Crompton was the first to adopt a low-cost air filled open design.
The Crompton arc tube is manufactured from Aluminosilicate glass sourced from GEC glassworks, and fabricated in the same way as an Osram lamp, making use of the efficient pinch-sealing technique and low cost drawn tubing rather than expensive hand-blown arc tube inners. A flared glass tube is fused into the dome of the outer bulb, and the arc tube is mounted between this flare and a similar double-ended flare to which the outer bulb is drop-sealed. Asbestos pads offer cushioning and permit thermal expansion of the arc tube. All that remained was for the outer bulb to be capped, and the slow, expensive exhaust process had been eliminated. However with the introduction of the more efficient Quartz MB type arc tube, this did require an inert atmosphere to protect the high temperature molybdenum seals. Crompton could not compete in this market and ceased mercury production when the MA market dried up.