Dipped beam (low beam, passing beam, meeting beam)

Dipped-beam (also called low, passing, or meeting beam) headlamps provide a light
distribution to give adequate forward and lateral illumination without blinding other road
users with excessive glare. This beam is specified for use whenever other vehicles are
present ahead. The international ECE Regulations for headlamps specify a beam with a
sharp, asymmetric cutoff preventing significant amounts of light from being cast into the
eyes of drivers of preceding or oncoming cars.

Main beam (high beam, driving beam, full beam)

Main-beam (also called high, driving, or full beam) headlamps provide an intense, centre-
weighted distribution of light with no particular control of glare. Therefore, they are only
suitable for use when alone on the road, as the glare they produce will dazzle other
drivers.

Auxiliary lamps

i Driving lamps

High beam headlamps augmented by auxiliary driving lamps

"Driving lamp" is a term deriving from the early days of nighttime driving, when it was
relatively rare to encounter an opposing vehicle. Only on those occasions when opposing
drivers passed each other would the dipped or "passing" beam be used. The full beam
was therefore known as the driving beam

Many countries regulate the installation and use of driving lamps. For example, in Russia
each vehicle may have no more than three pairs of lights including the original-
equipment items.

ii Rallye and off-road lamps

Vehicles used in rallying, off-roading, or at very high speeds often have extra lamps to
broaden and extend the field of illumination in front of the vehicle. On off-road vehicles
in particular, these additional lamps are sometimes mounted along with forward-facing
lights on a bar (commonly referred to as a light bar) above the roof, which protects them
from road hazards and raises the beams allowing for a greater projection of light forward.

iii Fog lamps

Front fog lamps provide a wide, bar-shaped beam of light with a sharp cutoff at the top,
and are generally aimed and mounted low. They may be either white or selective yellow.
They are intended for use at low speed to increase the illumination directed towards the
road surface and verges in conditions of poor visibility due to rain, fog, dust or snow. As
such, they are often most effectively used in place of dipped-beam headlamps, reducing
the glare back from fog or falling snow
OPTICAL SYSTEMS – Reflector Lamps

Lens optics

A light source (filament or arc) is placed at or near the focus of a reflector, which may be
parabolic or of non-parabolic complex shape. Fresnel and prism optics moulded into the
headlamp lens then shift parts of the light laterally and vertically to provide the required
light distribution pattern. The lens may use both refraction and TIR to achieve the desired
results. Most sealed-beam headlamps have lens optics.

Reflector optics

The optics to distribute the light in the desired pattern is designed into the reflector itself,
called an "optic reflector". Depending on the development tools and techniques in use,
the reflector may be engineered from the start as a bespoke shape, or it may start as a
parabola standing in for the size and shape of the completed package. In the latter case,
the entire surface area is modified so as to produce individual segments of specifically
calculated, complex contours. The shape of each segment is designed such that their
cumulative effect produces the required light distribution pattern.

Optic reflectors are commonly made of compression-moulded or injection molded

Dual-beam reflector headlamps

Night driving has long been dangerous due to the glare of headlights from oncoming
traffic which temporarily blinds approaching drivers. Headlamps that satisfactorily
illuminate the road ahead without causing glare have long been sought. The first solutions
involved resistance-type dimming circuits which decreased the brightness of the
headlamps. This yielded to tilting reflectors, and later to double-filament bulbs with a
high and a low beam. Automatic headlamp dimmers were also introduced.

In a two-filament headlamp, there can only be one filament exactly at the focal point of
the reflector. There are two primary means of producing two different beams from a two-
filament bulb in a single reflector

American system

One filament is located at the focal point of the reflector. The other filament is shifted
axially and radially away from the focal point. In most 2-filament sealed beams and in 2-
filament replaceable bulbs type 9004, 9007 and H13, the high beam filament is at the
focal point and the low beam filament is off focus. For use in right-traffic countries, the
low beam filament is positioned slightly upward, forward and leftward of the focal point,
so that when it is energized, the light beam is widened and shifted slightly downward and
rightward of the headlamp's axis. Transverse-filament bulbs such as 9004 can only be
used with the filaments horizontal, but axial-filament bulbs can be rotated or "clocked"
by the headlamp designer so as to optimize the beam pattern or to effect the traffic-
handedness of the low beam. The latter is accomplished by clocking the low-beam
filament in an upward-forward-leftward position to produce a right-traffic low beam, or
in an upward-forward-rightward position to produce a left-traffic low beam.
The opposite tactic has also been employed in certain 2-filament sealed beams. Placing
the low beam filament at the focal point to maximize light collection by the reflector, and
positioning the high beam filament slightly rearward-rightward-downward of the focal
point. The relative directional shift between the two beams is the same with either
technique—in a right-traffic country, the low beam is slightly downward-rightward and
the high beam is slightly upward-leftward, relative to one another—but the lens optics
must be matched to the filament placements selected.

European system

The traditional European method of achieving low and high beam from a single bulb
involves two filaments along the axis of the reflector. The high beam filament is on the
focal point, while the low beam filament is approximately 1 cm forward of the focal point
and 3 mm above the axis. Below the low beam filament is a cup-shaped shield (called a
"Graves Shield") spanning an arc of 165°. When the low beam filament is illuminated,
this shield casts a shadow on the corresponding lower area of the reflector, blocking
downward light rays that would otherwise strike the reflector and be cast above the
horizon. The bulb is rotated (or "clocked") within the headlamp to position the Graves
Shield so as to allow light to strike a 15° wedge of the lower half of the reflector. This is
used to create the upsweep or upstep characteristic of ECE low beam light distributions.
The bulb's rotative position within the reflector depends on the type of beam pattern to be
produced and the traffic directionality of the market for which the headlamp is intended.

Projector (polyellipsoidal) lamps

In this system a filament is located at one focus of an ellipsoidal reflector and has a
condenser lens at the front of the lamp. A shade is located at the image plane, between
the reflector and lens, and the projection of the top edge of this shade provides the low-
beam cutoff. The shape of the shade edge, and its exact position in the optical system,
determines the shape and sharpness of the cutoff. The shade may have a solenoid
actuated pivot to provide both low and high beam, or it may be stationary in which case
separate high-beam lamps are required. The condenser lens may have slight or other
surface treatments to reduce cutoff sharpness. Recent condenser lenses incorporate
optical features specifically designed to direct some light upward towards the locations of
retroreflective (A retroreflector is a device or surface that reflects light back to its source
with a minimum scattering of light) overhead road signs

Light sources

Incandescent light bulbs

Traditionally, an incandescent tungsten light bulb has been the light source used in all of
the various automotive signalling and marking lamps. Typically, bulbs of 21 to 27 watts,
producing 280 to 570 lumens (22 to 45 Mean Spherical Candlepower) are used for brake,
turn, reversing and rear fog lamps, while bulbs of 4 to 10 W, producing 40 to 130 lm (3 to
10 mscp) are used for tail lamps, parking lamps, sidemarker lamps and side turn signal
repeaters.

Halogen

Tungsten-halogen light bulbs are a very common light source for headlamps and other
forward illumination functions. Some recent-model vehicles use small halogen bulbs for
exterior signalling and marking functions, as well.
HID light sources (xenon and bi-xenon)

Xenon is currently the lamp used in single-source lighting systems being developed for
automotive use. HID stands for high-intensity discharge, the technical term for the
electric arc that produces the light. Automotive HID lamps are commonly called 'xenon
headlamps', although they are actually metal halide lamps that contain xenon gas. The
xenon gas allows the lamps to produce minimally adequate amounts of light immediately
upon startup and speed the warmup time. If argon were used instead, as is commonly
done in street and other stationary metal halide lamp applications, it would take several
minutes for the lamps to reach their full output. HID headlamps use a small, purpose-
designed burner which produces more light than ordinary tungsten and tungsten-halogen
bulbs. The light from HID headlamps has a distinct bluish tint when compared with
tungsten-filament headlamps. The high intensity of the arc comes from metallic salts that
are vapourised within the arc chamber.

The headlight pattern would not be limited to individual overlapping beams, but could be
channeled by electronic controls of the fiber optics to provide optimum visibility over an
extended range of driving conditions including in the fog, dust or snow. Individual lamps
would not be needed, just a mounting point for the optical fibers running back to the
single light source and computer controlled for colour, intensity and continuity.

HID headlamp bulbs produce between 2,800 and 3,500 lumens from between 35 and 38
watts of electrical power, while halogen filament headlamp bulbs produce between 700
and 2,100 lumens from between 40 and 72 watts at 12.8 V. Because of the increased
amounts of light available from HID bulbs, HID headlamps producing a given beam
pattern can be made smaller than halogen headlamps producing a comparable beam
pattern. Alternatively, the larger size can be retained, in which case the xenon headlamp
can produce a more robust beam pattern.

HID headlamp bulbs do not run on low-voltage DC current, so they require a ballast with
either an internal or external ignitor. The ballast controls the current to the bulb. When
the headlamps are switched on, the ignitor provides rapidly pulsed current at several
thousand volts to initiate the arc between the electrodes within the bulb. Once the arc is
started, its heat begins to vapourise the metallic salts within the arc chamber, and the
ballast gradually transitions from startup operation to arc-maintenance operation. Once
the arc is completely stabilised, the ballast provides 85 V in conventional D1 and D2
systems, or 42 V with mercury-free D3 and D4 systems.

The arc within an HID headlamp bulb generates considerable short-wave ultraviolet (UV)
light, but none of it escapes the bulb. A UV-absorbing hard glass shield is incorporated
around the bulb's arc tube. This is important to prevent degradation of UV-sensitive
components and materials in headlamps, such as polycarbonate lenses and reflector
hardcoats. The lamps do emit considerable near-UV light.

Neon tubes

Neon lamp tubes were introduced into widespread production for the CHMSL on the
1995 Ford Explorer, and notable later uses included the 1998 Lincoln Mark VIII, with a
neon tube spanning the width of the trunk decklid, and the BMW Z8, which made
extensive use of neon. Numerous concept cars have included neon lamp features, from
such manufacturers as Volvo. Hella offered an aftermarket neon CHMSL in the late
1990s.
The linear packaging of the neon light source lends itself to the linear packaging favored
for many CHMSL installations, and neon lights offer the same nearly-instant rise time
benefit as LEDs. However, neon tubes require an expensive and relatively power-hungry
ballast (power supply unit), and as a result, neon lights have not found significant long-
term popularity as sources of light for automotive signaling.

Light emitting diodes (LED)

The limiting factors with LED headlamps presently include high system expense,
regulatory delays and uncertainty, glare concerns related to the output spectrum of white
LEDs, and logistical issues created by LED operating characteristics. LEDs are
commonly considered to be low-heat devices due to the public's familiarity with small,
low-output LEDs used for electronic control panels and other applications requiring only
modest amounts of light. However, LEDs actually produce a significant amount of heat
per unit of light output. Rather than being emitted together with the light as is the case
with conventional light sources, an LED's heat is produced at the rear of the emitters. The
cumulative heat of numerous high-output LED emitters operating for prolonged periods
poses thermal-management challenges for plastic headlamp housings. In addition, this
heat buildup materially reduces the light output of the emitters themselves. LEDs are
quite temperature sensitive, with many types producing at 30 °C (85 °F) only 60% of the
rated light output they produce at an emitter junction temperature 16 °C (60 °F).
Prolonged operation above the maximum junction temperature will permanently degrade
the LED emitter and ultimately shorten the device's life. The need to keep LED junction
temperates low at high power levels always requires additional thermal management
measures such as heatsinks and exhaust fans which are typically quite expensive.

LEDs are being used with increasing frequency in automotive lamps. They offer very
long service life, extreme vibration resistance, and can permit considerably shallower
packaging compared to most bulb-type assemblies. LEDs also offer a significant safety
performance benefit when employed in brake lights, for when power is applied they rise
to full intensity approximately 200 milliseconds (0.2 seconds) faster than incandescent
bulbs. This fast rise time not only improves the attentional conspicuity of the brake lamp,
but also provides following drivers with increased time in which to react to the
appearance of the brake lamps.

The commercial vehicle industry has rapidly adopted LEDs for virtually all signaling and
marking functions on trucks and buses, because in addition to the fast rise time and
concomitant safety benefit, LEDs' extremely long service life reduces vehicle downtime.

Variable-intensity signal lamps

Internationalized ECE regulations explicitly permit vehicle signal lamps with intensity
automatically increased during bright daylight hours when sunlight reduces the
effectiveness of the brake lamps, and automatically decreased during hours of darkness
when glare could be a concern. Both US and ECE regulations contain provisions for
determining the minimum and maximum acceptable intensity for lamps that contain more
than a single light source.