Sylvania Warm Deluxe Mercury H33-1GL/WDX

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. 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.

In 1972 Westinghouse achieved a further improvement with its Style-Tone /N colour, which delivered a still warmer light but without the pinkish hue. That was achieved with a blend of yttrium vanadate and magnesium fluorogermanate, plus a light-scattering coating of fine silica powder that reflected transmitted blue back into the phosphor coating. In 1976 Sylvania adopted a similar principle with the launch of its Warmtone /N lamp, and the old /WDX was discontinued.
´╗┐Manufacturer: GTE Sylvania
Lamp Power: 400 Watts
Lamp Current: 3.25 Amps H33 or H1 Ballast
Lamp Voltage: 140 Volts
Cap Type: E39s/41 Ni plated brass + vitrite
Bulb Type: BT-117 BT-37 in eighths/inch
Bulb Finish: WDX Phosphor Leaded Borosilicate
Electrodes: Backwound tungsten Double carbonate emitter
Arc Length:
Atmosphere: Inner: Hg | Ar (5 atm) Outer: Nitrogen
Luminous Flux: 21,000 lm @ 100 hrs
Luminous Efficacy: 52.5 lm/W @ 100 hrs
Colour Temperature & CRI: CCT:3600K CRI: Ra47
Chromaticity Co-ordinates: CCx: 0.400 CCy: 0.380
Lifetime: 24,000h to 50% survival 10,000h to 70% lumens
Warm-up & Re-strike Time: 4 minutes 15 minutes
Burning Position: Universal Horiz. lumens 5% less
Overall Length: 292 mm 11┬Ż inches
Light Centre Length: 178 mm 7 inches
Factory: Drummondville Canada
Date of Manufacture: June 1973 Date Code: 30
Original Value: US $16.50 (1973)
References: 1) Sylvania Engineering Bulletin O-346, Mercury Lamps, April 1977 (USA).
2) Sylvania Lamp Catalogue, 1969 USA (/WDX lamps not yet listed)
3) Sylvania Lamp Catalogue, 1971 USA (/WDX 400W lamps listed)
4) Sylvania Lamp Catalogue, 1973 USA (/WDX 250W and 400W lamps listed.
5) Sylvania Lamp Catalogue, 1976 USA (/WDX 250W and 400W lamps listed, alongside the new /N in 175, 250, 400W)
6) Sylvania Lamp Catalogue, 1977 USA (/WDX lamps delisted and replaced by /N types).