HIGH-INTENSITYDISCHARGE HEADLIGHTSPARTS AND OPERATION High-intensity discharge (HID)headlights produce a distinctive blue-white light that is crisper,clearer, and brighter than light produced by a halogen headlight.High-intensity discharge lamps do not use a filament like conventionalelectrical bulbs, but contain two electrodes about 0.2 in.(5 mm) apart. A high-voltage pulse is sent to the bulb which arcsacross the tips of electrodes producing light.It creates light from an electrical discharge between two electrodesin a gas-filled arc tube. It produces twice the light with lesselectrical input than conventional halogen bulbs.The HID lighting system consists of the discharge arc source,igniter, ballast, and headlight assembly. b SEE FIGURE 56 19.The two electrodes are contained in a tiny quartz capsule filledwith xenon gas, mercury, and metal halide salts. HID headlights arealso called xenon headlights. The lights and support electronics areexpensive, but they should last the life of the vehicle unless physicallydamaged.HID headlights produce a white light giving the lamp a bluewhitecolor. The color of light is expressed in temperature using theKelvin scale. Kelvin (K) temperature is the Celsius temperature plus273 degrees. Typical color temperatures include:{ Daylight: 5,400°K{ HID: 4,100°K{ Halogen: 3,200°K{ Incandescent (tungsten): 2,800°KSEE FIGURE 56 20.HEADLIGHT AIMINGAccording to U.S. federal law, all headlights, regardless of shape,
must be able to be aimed using headlight aiming equipment. Older
vehicles equipped with sealed beam headlights used a headlight
aiming system that attached to the headlight itself. b SEE
FIGURES 56 22 AND 56 23. Also see the photo sequence on
headlight aiming at the end of the chapter.
LED HEADLIGHTS
Some vehicles, including several Lexus models, use LED headlights
either as standard equipment (Lexus LS600h) or optional. b SEE
FIGURE 56 21.
Advantages include:
{ Long service life
{ Reduced electrical power required
Disadvantages include:
{ High cost
{ Many small LEDs required to create the necessary light output
FIGURE 56 21 LED headlights usually require multiple units to
provide the needed light as seen on this Lexus LS600h.
FIGURE 56 22 Typical headlight aiming diagram as found in service information
FIGURE 56 23 Many composite headlights have a built-in
bubble level to make aiming easy and accurate.
FIGURE 56 25 A typical adaptive front lighting system uses two
motors: one for the up and down movement and the other for
rotating the low-beam headlight to the left and right.
FIGURE 56 24 Adaptive front lighting systems rotate the
low-beam headlight in the direction of travel.
FIGURE 56 26 Typical dash-mounted switch that allows the
driver to disable the front lighting system.
than normal if the rear of the vehicle is heavily loaded. b SEE
FIGURE 56 25.
When a vehicle is equipped with an adaptive front lighting system,
the lights are moved by the headlight controller outward, and
then inward as well as up and down as a test of the system. This
action is quite noticeable to the driver, and is normal operation of
the system.
ADAPTIVE FRONT
LIGHTING SYSTEM
PARTS AND OPERATION A system that mechanically moves
the headlights to follow the direction of the front wheels is called
adaptive (or advanced) front light system, or AFS. The AFS
provides a wide range of visibility during cornering. The headlights
are usually capable of rotating 15 degrees to the left and 5 degrees
to the right (some systems rotate 14 degrees and 9 degrees, respectively).
Vehicles that use AFS include Lexus, Mercedes, and
certain domestic models, usually as an extra cost option. b SEE
FIGURE 56 24.
NOTE: These angles are reversed on vehicles sold in countries
that drive on the left side of the road, such as Great
Britain, Japan, Australia, and New Zealand.
The vehicle has to be moving above a predetermined speed,
usually above 20 mph (30 km/h) and the lights stop moving when the
speed drops below about 3 mph (5 km/h).
AFS is often used in addition to self-leveling motors so that
the headlights remain properly aimed regardless of how the vehicle
is loaded. Without self-leveling, headlights would shine higher than normal if the rear of the vehicle is heavily loaded. b SEE
FIGURE 56 25.
When a vehicle is equipped with an adaptive front lighting system,
the lights are moved by the headlight controller outward, and
then inward as well as up and down as a test of the system. This
action is quite noticeable to the driver, and is normal operation of
the system.
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