||The SOX-PSG lamp was launched by Philips in September 2003 as the result of a successful attempt to eliminate early failures right up to the point of half its usual service life. This offers a tremendous advantage to end users who can avoid the great expense of carrying out spot-replacements, which were commonplace with previous SOX lamps which suffered a significant proportion of premature failures.
SOX lamps have always employed a getter of barium to maintain high vacuum in the outer jacket, thus preventing heat losses and ensuring that lamp efficacy remains high. However the barium film, usually deposited in the neck area of the lamp, is electrically conductive and can come into contact with lead wires emerging from the stem. The electrified coating can then cause decomposition of the glass stem by electrolysis, which may ultimately lead to leaks or cracking, and premature lamp failure. Additionally if the indium coating makes contact with this getter film, it can draw sodium out of the arc tube, leading to very severe blackening as the sodium vapour attacks the indium film. To minimise this effect, a gap in the indium film is left just above the getter, but heat can be lost, raising lamp watts.
The PSG lamp eliminates the traditional barium getter and employs the Philips Solid-state Getter instead. It consists of a zirconium-cobalt pellet mounted on a stalk beside the arc tube, and is equally effective both for producing the initial high vacuum in the lamp, and maintaining it throughout life. Because the conductive barium film is eliminated, lamp reliability increases dramatically and failures before 6,000 hours are eliminated. The platinum catalyst from SOX-E is also used to break down hydrocarbons for higher efficacy.