Automatic Headlight

Automatic Headlight Dipper Unit

ABSTRACT

The number of vehicles on our roads is burgeoning day by day. This is turn forced

almost all this vehicle manufactures to think about the extra safety instruments and

electronic controls to attach with these products for giving the users a safety derived in all

road conditions through a mass flow traffic. If asked, one should always mention that the

right driving is very cumbersome due to the dazzling light problems and the frequent

dipping of headlights by manual means that often causes fatigue to the driver particularly at

the time of peak traffic. So naturally to get rid of this perennial problem, an automatic

mechanism has to come up to dip the headlamp automatically whenever required. For

keeping a motor vehicle under perfect control and reins of the driver, different types of

controls and accessories are provided in an automobile around the driver’s seat, on the

dashboard and at the footboard. Simply, an automatic dipper is a unit, which can

automatically judge when the headlight beam needs to be lowered, and which dip the

headlamp from which beam to a dipped beam. As the dipper unit is well connected to the

lighting system of the vehicle, we have to look short into the type and construction of a

head light before discussing the wiring diagram or the construction of Automatic dippers.

INTRODUCTION

The number of vehicles on our roads is burgeoning day by day. This is turn forced

almost all this vehicle manufactures to think about the extra safety instruments and

electronic controls to attach with these products for giving the users a safety derived in all

road conditions through a mass flow traffic. If asked, one should always mention that the

right driving is very cumbersome due to the dazzling light problems and the frequent

dipping of headlights by manual means that often causes fatigue to the driver particularly at

the time of peak traffic. So naturally to get rid of this perennial problem, an automatic

mechanism has to come up to dip the headlamp automatically whenever required.

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For keeping a motor vehicle under perfect control and reins of the driver, different

types of controls and accessories are provided in an automobile around the driver’s seat, on

the dashboard and at the footboard. There are controls like clutch, brake pedal, accelerator

pedal, and sharing the same importance, the dimmer switch is changed with time, and its

pace in the filed of automobile safety is one of the uppermost.

Simply, an automatic dipper is a unit, which can automatically judge when the

headlight beam needs to be lowered, and which dip the headlamp from which beam to a

dipped beam. As the dipper unit is well connected to the lighting system of the vehicle, we

have to look short into the type and construction of a head light before discussing the

wiring diagram or the construction of Automatic dippers.

HEADLAMPS

The modern lighting system consists of switches, lamps, wiring harness, and fuses

or circuit breakers. It may be mentioned that the primary purpose of the headlight design is

to produce illumination over considerable distance ahead of the vehicle and enable the

driver to drive at reasonable speeds at night with safety. But the provision should also be

made that the drivers of other vehicles coming from the opposite direction to not experience

a glare. For this purpose a dipped or meeting beam is also provided for maintaining the

reasonable speed with safety without dazzling the coming driver. To prevent dazzle to the

on coming driver during particularly misty or hazy conditions the light about the horizontal

should be cut off. This is called dipping of the head light beam.

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In an average car, the lighting system consumes about 70 – 75% of electrical energy

when driven at night. In terms of amperage the consumption may be from 24 – 40 A at

night for al purposes including the radio, heater, and transmission controls.

Light Source

There are two kinds of light sources, namely, the one that emits light and the other

that reflects light. In the case of headlamp used in automobiles, both the things are

combines in A. The filament of the electric lamp is the primary source, while the reflector

is referred to as the secondary source. The intensity, colour and distribution are the

important characteristics of any light source.

The headlight is composed of three elements:

1. The light filament that gives off light when a current flows through it.

2. The parabolic reflector that reflect the light in front: and

3. The lens that refracts of distorts the light beam into an illuminating pattern.

Construction

The present day headlights are the outcome of a lot of research and development.

Earlier a single electric bulb of the carbon filament type was employed. The bulb was

placed at the focus of a parabolic silvered reflector in order to give a parallel beam of light.

The following figure shows a parabolic reflector with bulb, the lines showing light rays

emitted from the filament of the bulb in all directions. This type of headlight given a

parallel light beam, that saves greater illumination nearer the axis. It may be mentioned

that the bulb itself and the intensity of light fall off towards the outer portion of the beam

block a small amount of light.

From figure it may be seen that if the bulb filament is moved from position ‘d’, the

focus of reflector, to a position ‘a’, the light beam ‘abc’ will no longer be a parallel one but

will become divergent. On the contrary, if the filament is moved to position ‘f’ the beam

will take the course a shown by ‘fbg’ and will meet at a point on the axis of the bulb. It

may be mentioned that by a single adjustment of the bulb, the beam cane be concentrated at

a ore-determined distance ahead of the vehicle in order to give a spot light effect.

Formerly the headlight was provided with certain means of adjusting the bulb

holder with respect to the reflector along with the bulb axis in order to focus it. It had to be

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done up every time the bulb was changed. This was essential, otherwise it would cause

increased dazzle to other motorists. The filament is encased in an airtight bulb in order to

prevent burning up of the white-hot filament because of oxygen in the air. The reflector is

generally of polished metal and it throws all the light rays into a cylindrical beam.

The lens is made up of a number of glass prisms molded together and they bend the

beam of light into an oval pattern which is aimed ahead of the vehicle and somewhat in the

downward direction. A part of the light is spread out in front of the vehicle for providing

local illumination, whereas the rest of it is focused into a hot spot that provides distant

illumination.

The first major advancement in headlight design took place with the introduction of

pre-focused bulbs. It has two filaments, one for normal driving and the other for city

driving or for overtaking. These days even two sets of headlights are used for the above

said purposes. Generally a foot selector switch is provided, which enables the driver to

select either the normal driving or the passing beam.

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The parabolic reflector showing light

rays emitted from the filament of the bulb

The effect of changing the position of

filament on the nature of the light beam

Sealed-Beam Headlights

In a sealed beam headlight, the filament and the reflector along with the lens are

sealed in an airtight unit. The front face of the sealed beam unit is a lens, which is fused to

the reflector after the two filament units, has been inserted through the center of the

reflector and sealed in position. The complete unit is then evaluated and filled with inert

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gas. With these units the only service required is to aim them. This type of headlight

introduced in 1940 in the U.S.A.

Sealed beam headlights have the following advantages:

1. The glass unit is self-contained with accurately focused filaments.

2. Dust, moisture, etc. are prevented from entering from the back of the lens

and the reflector.

3. A greater amount of light is provided in the beam because, of the absence of

a filament bulb and

4. The beam of light obtained is greatly improved due to the pre-focused

filament and permanently bright reflector.

It is essential to have a provision for horizontal and vertical adjustment of the beam

by titling the sealed beam unit in its body housing. Two adjusting screws, as shown in the

following figure, generally do it. Fig. shows an improved version of a selected beam unit

with the provision of a metal mask or shield in front of the upper filament to prevent stray

light rays from escaping upwards and reflecting back to the eyes of the driver. This type of

headlights gives a brighter beam pattern and further reduces the repair and maintenance

time. Such type of units are, however, more expensive or replace than plain or pre-focused

type of units. Recently headlights of 50-60 W for the lower filament and 40-45 for the

upper filament have been used, thus increasing their light output.

Control of Headlight Beam

The circular beam can be spread horizontally to any desired extent with the help of

prisms, molded in the inside of the headlight cover glass, as shown in the figure. The

horizontal light intensity can be controlled in any desired way by a suitable design of the

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headlight. The circular beam can also be controlled in the vertical direction with the help of

prisms molded in front of the glass, thus redirecting the light rays in the downward

direction. This way the downward reflected beam does not obstruct the vision of the other

road users coming from the opposite side. With these two combinations, any required main

beam illumination, combined with side illumination nearer to the vehicle can be produced.

RECENT DEVELOPMENTS

Technology improves day and day in the field of automobile headlamp construction

and it left out the earlier single electric bulb of the carbon filament type and in place

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modern sealed beam headlights are using nowadays. The light circuits of today’s vehicles

can consist of more that 50 light bulbs and hundreds of feet of wiring. Incorporated within

these circuits are circuits’ protector, relays, switches lamps, and connectors. In addition

more sophisticated lighting systems use computers and sensors. The lighting circuit

consists of an array of interior and exterior lights, courtesy lights and so on. Federal laws

largely regulate the lighting circuits, so the systems are similar between the various

manufactures.

Halogen lamps

The halogen lamps are mostly introduced and consist of tungsten filaments in the

atmosphere of some halogen element such as chlorine, bromine, or iodine. The tungsten

evaporated from the filaments reacts with halogen gas to form tungsten halide, which is

decomposed back into halogen and tungsten due to high temperature at the filaments, thus

causing the tungsten to get redeposit on the filaments. In this way the life of the bulb is

increased.

Besides, the filament can operate at still higher temperature, which increases its

light intensity. However, the halogen attacks metals at cold temperatures. Thus other

metals within the enclosure, viz. the metal shield and the second filament, which is not

being used, are attacked by the halogen. To avoid this happening, pure halogen is replaced

by dibromomethane gas, which does not cause deterioration of the cold metals. With these

headlamps quartz glass is used since ordinary glass tends to crack due to higher operating

temperature.

Composite headlights

Many of today’s vehicles have a halogen head light system using a replaceable bulb.

This system is called composite headlights. By using the composite headlight system,

vehicle manufacturers are able to produce any style of headlight lens by desire. This

improves the aerodynamics, duel economy, and styling of the vehicle. Many manufacturers

vent the composite headlight housing because of the increased amount of the heat

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developed by these bulbs. Because the housing is vented, condensation is not harmful to

the bulb and does not affect the headlight operation. When the headlights are turned on, the

heat generated from the halogen bulbs will dissipate the condensation quickly. On systems

using non-vented composite headlights, condensation is not considered normal. The

assembly should be replaced.

HID Headlamps

High Intensity Discharge (HID) headlamps are the latest headlight development.

These headlamps put out three times more light and twice spread on the road then

conventional halogen headlamps. They also use about two-thirds less power to operate will

last two to three times larger. HID lamps produce light in tooth ultraviolet and visible

wavelengths. This advantage allows highway signs and other reflective materials to glow.

This type lamp first appeared on select models from BMW in 1993, Ford in 1995, and

Porche in 1996.

These lamps do not relay on growing filament for light. Rather light is provided as

a high voltage bridges an air gap between two electrodes. The presence of inert gas

amplifies the light given off by the arching. More than 15,000 volts are used to jump the

gap between the electrodes. To provide this voltage, only about 80 volts is required to keep

current flow across the gap. The great light output of these lamps allows the headlamp

assembly to be smaller and lighter. These advantages allow designers more flexibility in

body designs as they attempt to make their vehicles more aerodynamic and efficient.

HEADLIGHT DAZZLE

The dazzle effect is one of the major problems faced by a driver in night driving.

So one has to stop the high intensity light from the eyes of the incoming driver or road

users to prevent the dazzle effect. Automatic Dipper is one such mechanism, which is

employed for safety night driving without the intense dazzling effects. Without much

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efforts from the driver which otherwise has to dim the lights every seconds by manual

means may lead to fatigue to the driver especially during peak traffics. So it will be better

to know ‘what is meant by dazzle?’ and ‘what all devices are often used in preventing

dazzle effect?’ before mentioning the advantages and uses of an auto dipper.

The problem of headlight dazzle is linked with many factors of which, the human

eyes is the most important. In fact, it is the final judge in respect of dazzle and

illumination. It may be mentioned that for driving, bright illumination is essential. In

short, condition of illumination, should be such that there is clear vision for all motorists.

Dazzle is nothing but brightness, which causes interference with vision. The various

factors, which govern it, are: brightness, contrast, and the angle subtended by the bright

area on the eye. It is the contrast between the bright and dark areas, which is one of the

main causes of dazzle. However, it is difficult to lay down in terms of quantity the fixed

ratio of the brightness of the two areas which is likely to produce or eliminate the effect of

dazzle since it is controlled by the brightness of the lighter of the two areas. The ratio

between the absolute black area and a dimly lit area may be quite great but there will be no

dazzle effect. Further, an intensity bright area with very dark surroundings, does not give a

dazzling effect.

The dazzling effect can be prevented by,

Reducing the brightness of the headlights of the vehicles.

Stopping high intensity light from entering the yes of on-coming drivers or

road users.

Reducing the contrast between the surrounding area and the headlight of the

vehicle.

DIPPING OF HEADLIGHTS

When the vehicle is driven on the highways, it is required that light beam should be

of high density and should illuminate the road at a distance sufficiently ahead. However

when a vehicle coming in the opposite direction approaches a vehicle fitted with such

headlights, driver of that vehicle will experience a glare, which will blind him. To avoid

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this, a separate filament is fitted at such a position that that light beam from this filament is

deflected both down and sideways so that the driver of the oncoming car is not blinded.

Some of the ways in which this can be achieved are shown in the following figure.

The main filament may be placed at the focus with the dipper filament slightly

above it or the main filament and the dipper filament may be placed slightly below and

above the focus respectively, with the reflector tilted. Another popular method is to place

the main filament at the focus and the dipper filament slightly in front of the same with a

mental shield placed below the dipper filament. In this only this upper half of converging

beam comes out of the reflector. Thus it prevents the other rays from setting reflected from

the lower half of the reflector and emerging in the upward direction to cause glare. The

beam (main or dipper) are selected by the driver y means of a foot operated or steering

column mounted stick type dimmer switch but in case of automatic dippers the light from

the oncoming vehicle will trigger the dipper unit. The illumination of road by main bam

and the dipper beam is shown in the above figure.

Bifocal Bulb

In the earlier days, a dipping reflector was used as one of the popular anti-dazzle

devices. In this case, the movement of the reflector within the headlight casing dipped the

headlight beam. The solenoid, mounted at the back of the reflector, controlled the

movement of the reflector.

The bifocal both is an extensively used anti-dazzle device in the U.S.A and the U.K

this type of both has two filaments, one being either in front of or above the other filament.

The following figure shows this type of a bulb.

It will be seen that a metal shield is provided below the forward filament. Its main

purpose is to prevent the light rays from the filament striking the lower half of the reflector.

Switching over from one filament to the other may provide the normal and dipped beams.

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The figure & shows the manner in which the headlight beam is dipped while changing

over the normal to the dipped beam. The bifocal bulb is simple in installation and is also an

effective method of dipping the beam of the headlight.

Two Filament Bulbs

In two filaments modern headlights there uses a two-filament bulb with a fixed

reflector. In this case, one filament is meant for the dipping beam and the other main beam

filament is beneath it and it is located at the focus of the reflector. The nature of the dipped

beam can be controlled by the help of prisons and lenses provided at the front cover of the

headlight.

Anti-dazzle Devices

Most of the modern anti dazzle devices depend upon the redirection of the light

rays. This can be achieved by various ways as by lenses, by specially designed reflectors,

by bulbs of special design or by dipping reflector mechanisms. Now it is common practice

to control the beam from the driver’s seat, as and when required. If the initial focusing of

the lamp is correct, the dazzle effect is considerably reduced and at the same time it

provides sufficient illumination for the driver.

In the case, the upper and the lower levels of the reflector are displaced by an

amount equal to the filament length. It results in projection of light rays parallel and

downwards and not upwards. It may be noted the correct focusing of the filament with

respect to the two halves of the reflector will greatly help in the elimination of these upward

rays.

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Methods of getting dipped beams Bifocal bulb and the manner in which the headlight beam is dipped

A double – filament lamp

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AUTOMATIC DIPPER (AUTRONIC DYE)

Autronic dipper

An autronic dipper is a unit which can automatically judge when the head light

beam needs to be lowered. The auto dippers are basically switches, which dip the

headlamp from high beam to a dipped beam if a certain amount of light falls on its photo

sensor. This is a system, which electronically selects the proper headlamp beam for

country driving. It holds the lights on upper, or high, beam until a car trigger the system so

that it shifts the headlamps to the lower beam. When the other car had passed, the system

electronically shifts the headlamps back to the upper beam.

Location

As the operation of the auto dipper trigger out only when the light from the on-

coming vehicles falls directly on the photo sensor unit, it has to be ideally located in a place

where the light beams can freely entered without any obstruction. Commonly auto dipper

meters from the ground. The suggested position for passenger cars is in the place between

windshield and rear position f cabin rear view mirror.

Applications

Some American manufactures have first used photoelectric cells for automatic

dipping of headlights. In the ‘Autronic Eye’, the photoelectric cell senses the intensity of

light from the oncoming vehicles and dips the heedful accordingly; the driver does not have

to control the headlights. This type of system is very successful on American roads. But

on Indian roads with frequent curves etc., especially in case of rural areas and with non-

uniform light intensities automatic dipper has got not much use. But in high way driving

through level straight roads having a large number of vehicles and without having sharp

turns etc., the automatic dipper helps the drivers in eliminating the fatigue of operating the

dipper switch intensity level will always be there for satisfying he minimum intensity

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needed for the system to function even on small breathing turns which is often seen in high

ways.

Possibility of Manual Override

As the automatic dipper is particularly designed and good for the high way driving,

but the vehicle is meant for all type of roads, and for facing some particular situation where

the driver needs more light to see by etc., manual override is also fitted with the automatic

dipper unit by which the driver can operate the heedful becomes manually leaving out the

auto system inoperative. The driver has a sensitivity control, which allows adjustment of

the system to the surrounding light.

The override system can be used when the oncoming driver does not dim, the driver

needs more light to see by and also on rural road where not much vehicles are there at night

and also sharp turns are there.

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WORKING OF AUTO DIPPER

Automatic headlight dipping automatically switches the headlight from high beam

to beams when light from oncoming vehicle strikes the photocell or phototube (Photo

amplifier) of the vehicle. Thus we can select the proper headlight during country driving

and it saves the driver from the trouble of depressing the foot switch for lowering this

headlight beam. It holds the lights on the upper beam until the vehicle approaches from the

other direction. And also the moment the other car passes by, it shifts automatically the

headlights back to upper beam. The auto dipper is a device, which is highly immune to

lights from street lamps, roadside light sources and other manual sources of light.

Modern automatic dipping systems use solid-state circuiting and electromagnet

relays to control the beam switching. Most systems consist of the following major

components.

1. Light sensitive photocell

2. High-low beam relay

3. Sensitivity control

4. Amplifier

5. Dimmer and auxiliary foot switch

6. Wiring harness.

We can analyze the working of the system by considering the following schematic

circuit diagram of the auto-dipper.

The phototube is a variable resistor that used light to change the existence. The

phototube amplifier is usually mounted behind the front grill or on the one side of the

dashboard or in the rear view mirror support where it will be in limn with the light from the

vehicle approaching from the opposite direction. The sensitivity control sets the intensity

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level at which the photocell amplifier will energize. This control of set by the driver and is

located next to, or is a part of, the headlight switch assembly. The sensitivity control is a

potentiometer that allows the driver to adjust the sensitivity of the automatic dipper

(dimmer) system to surrounding ambient light conditions. The driver is able to adjust the

sensitivity level of the system by rotating the control knob. An increase in the sensitivity

level will make the headlights switch to the low beams sooner (approaching vehicle is

further away). A decrease in the sensitivity level will switch the headlight to low beams

when the approaching vehicle is closer. If the knob is located at full counter clockwise

position, the system enters manual override. The high-low rely is a single pole, double

throw unit that provides the switching of the headlight beams.

When the light from the oncoming strikes the light sensitive plate provided in it, an

electric current is released. When the oncoming vehicle is nearing, its strong light sets the

amplifier unit into operation. A special electronic tube is contained in the amplifier unit

know as thyraton, which amplifies the current entering its grid. The thyraton greatly

amplifies the current provided by the phototube. It becomes strong enough to put the

power relay unit into operation.

Schematic Circuit Diagram of an Autronic Eye

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The windings of the power relay are connected to the thyraton. There are two sets

of points provided when the upper contacts are closed, the high filament of the headlight is

connected to the battery. When the lower contacts are closed, the low filaments are

connected to the battery. Depending upon the strength f the current from the thyraton, the

points open and close lighting the upper or lower beam.

An auxiliary foot switches also provided in addition to this arrangement which this

the driver can hold the upper beam on, even though the auto-dipper has operated, this

shifting the headlights to the lower beam. This switch is used when signaling to the other

motorists.

The above figure shows the simplified schematic diagram of the auto-dipper

(autronic eye). The switches, resistance units, and other components are not shown. The

curve in the phototube indicates the light sensitive plate. The dotted line in the thyraton

unit indicates the grid.

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CONCLUSION

Newer and better technologies always come with time and it will help in reducing

the manual labor and difficulties in the sectors where it is made use. And in our case, the

auto dipper can perform a great deal in reducing the manual efforts and fatigue of drivers in

dipping the headlamp frequently while driving through highways full of moving vehicles.

However, vehicles employed with automatic dippers are not very often seen in our cities,

and it may be due to lack of information about the system and also because of giving

attention to the people saying that it is not at all practicable in our highways. Yes, of course

it has got some drawbacks like that one which is most common, when we drive the vehicle

fitted with automatic dippers on a road in which different types of vehicles and hence

varying light intensities cause frequent flickering of the headlight. And also the operation

of the system eliminated or reduced by devising newer methods and technologies. The one

nowadays available is only useful in highways and straight width roads.

Truly speaking, auto dippers are devices, which will attain more and more

importance in the forthcoming years. In short, it is a device with a very bright future. The

number of vehicles and the condition of the roads are improving very fast and the day is

near, when the driving regulation, nature of traffic etc., are growing up to the levels which

is already their in countries like America who successfully using auto dippers in their

highways.

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REFERENCES

1 AUTOMOTIVE ELECTRICITY, ELECTRONICS AND COMPUTER CONTROLS

- Barry Hollem Beak

2 AUTOMOTIVE ELECTRICAL EQUIPMENT – P.L. Kohli

3 AUTOMOBILE ENGINEERING – Kirpal Singh

4 AUTOMOBILE ENGINEERING – R.B. Gupta

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Automatic Headlight