IAEEL newsletter 3-4/97
Low frequencies and other ceramic updates
Low frequencies and other ceramic updates
Osram is following Philips´ path in ceramic metal-halides by currently testing its lamps with lower frequency electronic ballasts.
In reaction to the article "metal halide lamps use more ceramics" in IAEEL newsletter 2/97, both Osram and Philips clarified that the increase in system efficacy is due more to the fact that the ceramic discharge tube allows for higher operating temperatures than to the properties of the electronic ballasts (Ms. Yoko Hoshi of Osram pointed out that the ceramic burner runs about 100 degrees hotter than a normal quartz metal-halide (MH) burner, not 200 degrees C, as stated in their Hannover 1997 catalogue). Mr. George Kok at Philips pointed out that the main features of their electronic, low-frequency gear (200Hz) is the absence of visible flicker, which is typical for 50Hz systems, and some further improvements in color spread and life that can be ascribed to the constant power output. For 220240V systems, the efficacy improvement due to the ballast is only 1-2 lm/W compared with standard ballasts. For lower-voltage (100120V) systems, as in North America, the savings are greater owing to the inefficiency of the conventional (CuFe) gear, according to Mr. Kok, who also says that ceramic lamps cannot be operated on high-frequency gear (1 kHz) because acoustic resonance will damage the lamps.
As for Osram, Ms. Hoshi clarifies that Osram never officially recommended their electronic high-frequency Powertronic ballast for ceramic lamps. The company is currently testing ceramic MH lamps with their 120 Hz version of the Powertronic ballast.
The typical improvement in ceramic MH color rendering versus quartz lamps is Ra 810 points for lamps of similar color temperature, according to Philips.
Furthermore, Philips claims that their measurements show that ceramic lamps require less maintenance than quartz lamps. With a standard 50-percent failure rate, lamps in vertical burning positions will last for at least 9000 h, and those burning in a horizontal position will last for 12 000 hours, or longer. Hot restrike is not possible yet, but it may be with new ballasts.
Nils Borg