Further details on many of these phosphors can be found at
http://www.lamptech.co.uk/Documents/M14%20Phosphors.htm/C = Colour Improved. (MFG / Magnesium Fluoro-Germanate MgFGe04:Mn4+)
This was the first important mercury lamp phosphor, invented by Luke Thorington of Westinghouse in 1950. It offered high temperature stability and a moderate colour rendering thanks to a red ratio of about 7.5%, however these lamps appear somewhat greenish. The phosphor has a slight yellow colouration, which absorbs some of the blue light from the mercury discharge, thus rendering the mercury green radiation relatively more powerful than normal. For fifteen years this was the worlds' principal mercury lamp phosphor. It was favoured for indoor lighting where colour rendering is important.
/W = White. (Strontium orthophosphate, eg (Sr,Mg)3(PO4)2:Sn2+))
This later development was intended to raise the light output of mercury lamps, but without increasing significantly the colour rendering properties. Owing to the white body colour of the phosphor, it does not absorb blue wavelengths so more radiation from the mercury discharge is able to escape. Since it does not filter the discharge, the colour also appears white. However there is reduced red content (only abot 5%) so the colour rendering properties are inferior to /C. This lamp type was popular in outdoor and industrial areas where colour rendering is less imoortant.
/Y = Yellow. This was basically the /C lamp with an additional yellow filter.
/X = Purple Stained. This Sylvania invention was basically also the /C lamp but with a purple filter to lessen the strength of the mercury green lines, and achieve a lower colour temperature light having a warmer appearance for indoor lighting. It only existed for a couple of years.
/DX = Deluxe. (Yttrium Vanadate YVO4:Eu3+)
This most important of the phosphors was invented by Frank Palilla and Albert Levine of Sylvania in 1964. It offers high temperature stability combined with better colour rendering than /C or /X and higher light output than /W, and a red ratio of 11%. It therefore made all three of those colours obsolete virtually overnight in all countries of the world except the Americas, and continues to be used today (although mainly now in Yttrium Phosphate Vanadate version which is slightly better again). Due to the Europium metal content it is a much more expensive phosphor than its predecessors and lamp prices were somewhat higher. These could be justified everywhere except USA where energy is traditionally very cheap (so payback times would be slow), and where it is traditionally always difficult to up-sell consumers to higher priced lamps offering better performance (which is excellent of course for lamp collectors since so many old designs are still fairly easy to obtain!). During a period of about 25 years however it did eventually succeed to dominate the Americas as well.
/R = Beaty Light (Yttrium Vanadate + suspected Strontium chloroapatite).
This was a Westinghouse development of the 1970s which attempted to improve on /DX. It in fact consists mainly of DX phosphor mixed with a second blue-radiating component, probably strontium chloroapatite, which serves to decrease the relative intensity of the mercury green lines and achieve a warmer colour tone. Red ratio is about the same as /DX lamps but the colour temperature is lower. It was not a great success and was only made for a few years.
/N = Natural (Yttrium Vanadate + Ce:YAG)
Another Sylvania development from 1975 which lasted in production only up to 1985, this was a mixture of the DX phosphor with cerium doped YAG, which has a strong yellow body colour. It offers a very low colour temperature of only 3000K and a high red ratio of 14%. It made a good colour match with incandescent and at one time was popular for indoor shop lighting, but was eminently superseded by metal halide developments.
