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In 2005 Philips introduced its 2nd generation ceramic metal halide technology, MasterColour Elite, a major improvement beyond the original CDM lamp of 1994. Whereas competitors chose mechanically-based improvements such as GE's 3-piece injection moulded arc tubes, and Osram's rounded Powerball arc tubes, CDM Elite marked the first notable performance breakthroughs based on a new lamp chemistry.
This lamp retains Philips' original 5-piece cylindrical ceramic arc tube, but with dramatically reduced dimensions - the 70W model being similar to the traditional 35W size. Ordinarily such an increase in wall loading would result in short life due to accelerated corrosion of the ceramic by the rare earth halide salts, along with thicker tungsten deposits from the electrodes leading to reduced light transmission. As detailed in International Patent WO2003/060949 the addition of 25-35% calcium iodide reduces the rate of corrosion, while a small trace of calcium oxide facilitates a tungsten-halogen cycle to prevent blackening.
This allows a reduction in arc tube volume, and the resulting increase in wall loading boosts the colour rendering index above 90, and luminous flux by about 7%. Moreover the hotter arc tube can be dimmed to about 60% of rated power while holding the colour temperature constant and CRI above 75. As such, combined with a new electronic ballast, CDM Elite became the worlds first dimmable metal halide system. Unfortunately it was hampered by quality problems, and Elite became known as Delete as it was swiftly withrawn from the market for a painfully long 2 years of redevelopment. The 2nd generation CDM Elite was eventually re-launched in 2007, although regrettably without dimming capability. |