The HID headlamp system has a newly developed mercury-free discharge bulb, as well as a controller (ballast) that controls lighting of the discharge bulb.
KOITO and Philips developed the mercury-free discharge bulb using a mercury substitute. KOITO and DENSO developed the ballast for lighting the mercury-free discharge bulb. Together, these developments led to the world's first mercury-free HID headlamp system that provides bright lighting and long bulb life, equal to the conventional HID headlamp system.
"In 2003, about 20 percent of new vehicles had the HID discharge system in Japan," said Mikio Tsuruta, director, General Affairs Department of KOITO Manufacturing Co., Ltd. "But we expect our mercury-free HID discharge system will expand the HID system share worldwide."
In addition to adopting the mercury substitute for the bulb, the bulb tube design was changed to maintain the long bulb life.
To control the lighting of the newly developed mercury-free discharge bulb, the ballast was improved to apply increased initial operating wattage and operating current to the bulb.
"Our ballast achieves an approximate 50 percent reduction in volume and 25 percent weight reduction over conventional ballasts, despite its increased initial operating wattage and operating current," said Hiromi Tokuda, managing officer of the Powertrain Control Systems Business Group, DENSO Corporation. "We achieved these reductions by increasing the switching frequency of the DC-DC converter contained in the ballast and enhancing the heat resistance of the ballast."