HID lamps have no conventional filament. There are two electrodes, metal salts & gasses inside the bulb. An electrical arc, much like a tiny lightning bolt, is formed between the electrodes when power is applied.
If you watch HID bulbs fire up, you can actually see them "arc up". (Simple things amuse my simple mind...)
Wait - it gets even better - shortly after the arc is achieved, the metal salts evaporate and the fourth state of matter, plasma, is formed, and you know we likes us some
plasma. 
Hopefully this helps explain why oncoming traffic high beams an HID laden vehicle - they're being blinded by science.
