Kato, K. and Kunieda, Y., "Development of Mercury Free HID Ballast," SAE Technical Paper 2005-01-1012, 2005, doi:10.4271/2005-01-1012.
One of the key ingredients in a conventional high-intensity discharge (hereafter called “HID”) bulb is the heavy metal mercury. Legislation for mercury-free HID bulbs was proposed by the Japanese government in the year 2000 and backed up by the international lighting community adding two new categories of mercury-free HID bulb (D3 and D4) to ECE 99 in March of 2004. While conventional mercury-containing HID bulbs allow bulb voltage to vary between 20V and 85V during run-up to steady state operation, the range for mercury-free HID bulbs is only from 26V to 42V. This limitation required the development of a different power control algorithm. During initial investigation of the mercury-free bulb, a drastic variation in bulb voltage was noticed during bulb run up when the metal halide first begins to emit light. This discovery led to the development of a new control strategy for system warm up.