BY MATT STROUD AND PAUL BINDON
As you are driving one evening, you round a corner, and all of a sudden you are blinded by bluish-white beams piercing the dark. Have you come face to face with a UFO? A 747’s landing lights? The entrance to the Pearly Gates? No, you have just witnessed high intensity discharge (HID) lighting at its finest.
Today, HID lighting seems to be installed in all kinds of vehicle makes and models. It used to be only in high-end BMW or Lexus models, but now it is in that multicolored 1985 Honda Civic, truck accessory lighting, and motorcycles. You might even have it installed on your fire apparatus as floodlights.
HOW HID LIGHTING WORKS
The use of HID lighting began in the early 1990s in higher-end European car models. The U.S. and Japanese car manufacturers adopted the HID system in the mid-1990s. Lincoln, Acura, and Lexus were just a few of the companies using this technology. Since then, almost all manufacturers have offered models with the HID headlight system as standard or optional equipment.
How do the HID systems work? To better understand this new technology, you must first have a good idea of how conventional headlight systems function. Conventional systems use a bulb containing a filament that produces light when voltage is applied; just like a standard lightbulb you use in your home, these bulbs have a short life span and are fragile. The light produced has a yellowish hue and is rated in watts. Most conventional headlight systems are Department of Transportation-rated at 55 watts, and the voltage they use to produce their light is 12 volts.
HID headlight systems work differently. Rather than using a filament, the HID bulb is comprised of a quartz capsule that contains xenon gas, mercury (2004 and earlier HID bulbs), and metal halide salts with tungsten metal electrodes at each end. A high-voltage current produced by the HID control unit in each headlight assembly forms an arc in the capsule. This control unit draws 12 volts from the vehicle and steps it up to as much as 25,000 volts.
Figure 1. Operation of an HID System
Think of it as a controlled lightning strike in a small bottle. The light emitted from this process is rated about 4,000 Kelvin (K). A Kelvin rating is a method used to describe theoretical temperature of color. To put this in perspective, a conventional headlight bulb is rated about 2,800 K, which produces a yellow- or amber-colored light. A halogen headlight bulb is rated about 3,200 K. These bulbs produce a much whiter color of light. HID bulbs produce a bluish-white color of light, rated about 5,000 K, which is closest to natural sunlight at midday. Emitting this color of light from the front of a vehicle at night allows the operator to see and react faster and more accurately to obstacles in the road.
This is normal operation in a vehicle driving down the road. What happens when the vehicle crashes? As emergency first responders, you know that nearly 99 percent of vehicles in accidents sustain some sort of damage to the front end. The headlights are probably broken. What about that nice bluish-white, light-emitting, 25,000-volt headlight system?
The HID system does not care that the car has been damaged; the system is still trying to function. The controlled lightning strike we mentioned still needs a place to go. This can create a serious hazard for first responders who could come in contact with this extremely high voltage. To put this in context, if you have ever been shocked by a spark plug wire on a lawnmower or vehicle, you probably remember how that felt. The HID system voltage is a constant 25,000 volts and works more like a Taser® or stun gun. It has a higher refresh rate and therefore a much higher shock danger and can also pose a greater risk of igniting a fire.
When responding to a motor vehicle accident, you commonly need access to the engine compartment for fire suppression or to disable the 12-volt battery. When you attempt to open the hood, if your hands (or other body parts) come in contact with the rogue high-voltage arc, involuntary convulsive reactions can cause personal injury, and you will likely be thrown from the vehicle. However, if the HID system has been damaged, the vehicle body itself will not be charged with high voltage—your body must come in contact with the arc. Since the HID output is a low-amperage system, the risk of death by electrocution from this system is very low.
Now that you know the facts, you must take care when approaching the front of any vehicle with an HID lighting system. It is important to know that simply turning the ignition off will not turn off the headlights on most vehicles. They will remain operational until you turn them off at the switch or disconnect the 12-volt battery. You must disconnect the 12-volt battery to disable the supplemental restraint system (SRS) air bags, and this will also disable the HID system.
Note: The 12-volt battery may not be under the vehicle hood. Alternate locations for battery placement are becoming more common, especially on hybrid vehicles.
As you can see, vehicle technology has advanced to the point where first responders’ jobs have become more complicated and potentially hazardous. Hybrids, alternative fuel vehicles, SRS air bags, and complex body structures are just some of the technologies that can present complications and hazards when you are performing a rescue or an extrication. Up-to-date training has become one of the most critical tools when dealing with all of these technologies.
MATT STROUD is a 23-year veteran of Toyota Motor Corporation; he is a Toyota certified master diagnostic technician and an ASE certified master diagnostic technician, with 10 years certified in hybrid technology. He founded MGS TECH in 2007 with the goal to teach firefighters/EMS personnel how to safely manage hybrid and new technology vehicle incidents.
PAUL BINDON is an ASE master certified auto technician with more than 23 years of experience in the automotive field. He has been employed with Lexus Dealerships for the past 16 years, receiving master diagnostic specialist and hybrid certification through factory training in the latest automotive technologies. He joined MGS Tech in 2008 as a research specialist and an on-site trainer and has completed extrication training at the Corona-X seminar.
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