SON-T 250W High Pressure Sodium

This lamp represents the standard style of SON lamp being manufactured by Philips at the start of the 1980s, shortly after production had relocated from Eindhoven to Belgium.

The arc tube is of densely sintered polycrystalline alumina as manufactured at Philips' ceramic facility in Uden, the Netherlands. The electrical feedthroughs take the form of thin-walled niobium-1% zirconium tubes, into which an electrode is brazed with a titanium alloy. The backspacing of the electrodes is set by scraping the tips of three small knives into the side of the niobium, working towards the electrode end. This not only makes a scratch in the niobium surface, but also scrapes back a small amount of this soft alloy such that three small ridges of raised metal are left at the end of the scratch marks. These ridges make the tube too large in diameter to fit into the plugged end of the PCA tube and they effectively set the electrode insertion depth.

Arc tube seals are of the monolithic type in which the tube ends are initially partly closed by an annular plug, with a hole only a fraction larger in diameter than the niobium feedthroughs. Once one electrode assembly is inserted a small ring of frit glass is dropped over it, and fused in a vacuum furnace, filling the interface between niobium and PCA. The amalgam dose is added and the second seal made in a xenon atmosphere which forms the final arc tube fill.

The mount assembly is of the classic Philips style in which the number of welds is reduced by making use of a single long frame wire extending from the stem press. Expansion of the arc tube is catered for by a free-moving lower end, and a traditional barium getter ensures high vacuum quality.
Manufacturer: Philips Lighting
Lamp Power: 250 Watts
Lamp Current: 3.0 Amps
Lamp Voltage: 100 Volts
Cap Type: E40s/45 Nickel plated, vitrite
Bulb Finish: Clear Hard glass
Bulb Type: T-46 T-14½ in eighths/inch
Overall Length: 257 mm 10 1/8 inches
Light Centre Length: 160 mm 6¼ inches
Arc Length:
Electrodes: Backwound Tungsten Barium Calcium Yttrate
Atmosphere: Na,Hg | Xe Outer: Hard Vacuum
Luminous Flux: 26,000 lm (@ 100 hrs) 25,000 lm (@ 2,000 hrs)
Luminous Efficacy: 104.0 lm/W (@ 100 hrs) 100.0 lm/W (@ 2,000 hrs)
Colour Temperature & CRI: CCT: 2000K CRI: Ra 23
Chromaticity Co-ordinates: CCx: CCy:
Burning Position: Universal
Rated Lifetime: 24,000 hours to 50% survival
Warm-up & Re-strike Time: 4 mins (to 90% lumens) 15 minutes max
Factory: Turnhout Belgium
Date of Manufacture: March 1980 Date Code 0C
Original & Present Value:
References: 1) Philips UK Comprehensive Catalogue, 1980.