HID headlight

HID headlight terminology

An HID headlight bulb requires much higher current than a Halogen bulb to start the arc and build brightness to a steady state. So there are really three current levels; striking current, run up current and stead state.

HID headlight bulbs require AC current, so the ballast not only boots voltage, but also acts as an inverter, changing DC to AC current at around 250 to 450Hz.

HID Striking Current

The amount of amps and voltage needed to start the arc. During the strike phase, the ballast consumer about 6.5-amps per HID bulb and generates approximately 25,000 volts. A traditional halogen bulb consumes 4.2-amps and runs at normal battery voltage, around 12-14 volts.

HID Run up current

HID Run up current is the power used after the arc is struck and the bulb is dim but building brightness rapidly to its steady state. The Run up period, where the HID bulb builds heat and brightness lasts only a few seconds.

Steady state current

As the bulb reaches it’s full brightness and stabilizes (around 15-30 seconds after striking), it draws less power— around 3.8-amps per bulb. the ballast drops This is the very high current needed to start the arc inside the HID bulb.

HID Ballast

A step up transformer and inverter that converts 12-volts DC to AC voltage

HID Igniter

A step up transformer that step up voltage from the HID ballast to achieve a 25,000 volt striking voltage

HID bulb

An HID bulb contains two electrodes and two quartz envelopes to withstand the burn temperature of up to 1,500°F.. The inner envelope is filled with Xenon gas and a small amount of mercury and metal salts. It contains two electrodes. When a powerful current is applied to the electrodes, it lights an ARC, forming two bright or “hot” spots, one near each electrode. The arc is ionized gas that produces a plasma discharge that generates high intensity light.

©, 2018 Rick Muscoplat