 |
In 1964 Sylvania made a major breakthrough with the invention of yttrium vanadate phosphor. Originally intended as an improved red emitter for the company's cathode ray tubes, its high efficacy and thermal stability also made it an excellent phosphor for mercury lamps. This led to Sylvania's introduction of the Deluxe Mercury (DX) lamp in 1966.
Despite the notable improvement in red content and colour rendering, the colour temperature was still rather high. Between 1969 and 1971 Sylvania therefore introduced the Warm Deluxe (WDX) mercury lamp featured here. It is believed to employ a thicker coating of the same vanadate to deliver even more red. This caused a decrease in colour temperature to around 3300-3600K (depending on wattage) which made it more acceptable for indoor lighting. However the chromaticity is shifted slightly below the blackbody locus which gives it a pinkish colour. The extra absorption also decreases the light output about 6-9% vs regular DX lamps, and due to the greater proportion of light generated by the phosphor the lumen maintenance and life was inferior.
In 1975 Westinghouse achieved a further improvement with its Style-Tone /N colour, which delivered a still warmer light but without the pinkish hue. That was originally achieved using a blend of both yttrium vanadate and the earlier magnesium fluorogermanate phosphors. In 1976 Sylvania adopted the same principle with the launch of its Warmtone /N lamp, and the old /WDX was discontinued.
This particular lamp is old enough to still feature the famous Sylvania girder-frame unitised mount assembly, which delivered a notable improvement in mechanical strength. |