| THE
CONCEPT OF AUTO DIPPING.
In an automobile headlight, a 'meeting' beam (dip beam) is
provided in addition to the driving beam (high beam) so as
to reduce the dazzle for those approaching head-on to the
vehicle.
The Auto Dipping Device for a head light
is intended to automatically change the Headlight Circuit to
either driving beam or dip beam given a particular set of
road conditions, without the intervention of the driver. The
present practice is to operate the dip switch manually.
The function of the headlight is to
illuminate the road ahead of the automobile so as to reveal
objects ahead from a safe distance; at the same time it
should cause minimum discomfort and glare for drivers coming
from the opposite side.
The most extensively used and universally
accepted anti-dazzle arrangement is the bifocal or double
filament bulb. These bulbs have two filaments in which one
filament is positioned in relation to the reflector to give
the main forward beam, while the other filament gives the
dipped beam. The driver controls this system; either by a
foot operated switch or by a switch mounted on the steering
column.
Problems
associated with manual dipping:
Manual dipping is not being done
satisfactorily in India due to a variety of reasons, which
includes sheer physical strain involved in operation of the
dipper switch hundreds of times every night. (The total for
a single night will be 1000 if we consider 8 hours of
traveling and one encounter every one-minute and could
exceed this number if one travels on roads with dense
traffic). The other reason includes a general tendency of
paying more attention to steering control at the cost of
dipping during a critical vehicle meeting situation
especially in the case of heavy loaded vehicles. More
reasons are the physiological and psychological state of a
driver, which is influenced by a variety of factors like
working hours, economic issues and social factors etc.
Another major cause is 'ego problem', which makes each one
wait till the other person initiates dipping, which may not
happen.
Studies on
dipping practices on Indian Roads:
A study carried out by Central Road
Research Institute, New Delhi, (Road Research Paper No.216),
reveals the poor state of affairs on the Indian roads,
regarding dipping.
The observations and recommendations of
the study group on road safety constituted by the Government
of India vide Resolution No.19T (14) 68, dated June 3, 1969,
is as follows:
6.1.6 Night Driving
"A frequent cause of accidents at nights
is the glare caused by oncoming vehicles which momentarily
blinds the driver's vision. It takes three to eight seconds
for a person with good eyesight to recover from the glare
and during this time the vehicle will have covered a long
distance in utter darkness and it will be sheer luck if it
escapes an accident. A glare recovery test should be carried
out to gauge the applicant's ability in this direction,
followed by tests pertaining t color and night blindness."
3.1.1.4 Driving at Night with Main Beam
of Headlights ON
"This is one of the common failings
of our drivers in night driving, specially on dark or badly
lit roads that we generally have in rural areas and also
along many of the roads in our cities and towns. Driving
courtesy imposes a special responsibility on the driver,
that the oncoming driver is not handicapped by the dazzle of
headlights. To avoid this, it is imperative that as the
vehicles approach from opposite directions, the main beams
should be switched OFF and the dipped beams used instead, so
that the two vehicles can pass each other safely. Country to
the above requirement, many of our heavy vehicle drivers are
given to the practice of blinding oncoming vehicles drivers
by using both the main and dipped beams of their headlights
simultaneously, to gain on advantage over the oncoming
driver."
While the above refers to the culture of
road users, the road situation itself is disheartening in
our country. The highways in developed countries are mostly
of 6 lanes divided type, meeting very good geometrical
requirements so as to minimize glare whereas in India only
1.48% of the total length of National Highway is of the
standard multi-lane type (Source: Basic Road Statistics of
India, Ministry of Surface Transport Government of India).
The observations of the study group on
road safety (Constituted by Government of India vide
Resolution No.19 (14) 68, June 3, 1969) regarding the
conditions of our national highways are:
"The Indian roads are all essentially
very narrow, tortuous in their alignment and suffer from
many inadequacies, vis-à-vis the present day motor traffic
which has registered a phenomenal increase during the
post-Independence period. The other conditions of the roads
like poor shoulders, narrow culverts and bridges, sharp and
numerous curves and steep gradients which limit the sight
distance, numerous low level causeways and submersible
bridges are perennial hazards. All the above tell on the
nerves of the driver, causing fatigue and leading to errors
and misjudgment while driving.
All the above indicate the importance of
dipping of headlights in a country like India, so as to
avoid the problem of glare which impairs the visibility
which is vital for safe driving in a meeting situation
during the night. This leads to the conclusion that an Auto
Dipping Device can go a long way towards safety enhancement.
Driver Vision and Glare
The human eye, one of the most complex
organs and the greatest gift of nature, is equipped with a
variety of adaptation abilities. However, it is
incapacitated by glare.
The human eye's inability to refuse glare
sources in the normal visual field (the sun does not fall in
the normal visual field) during the long evolution process
might be because nature was unaware of man's potential to
create disabling sources-the most serious of which is
vehicle headlight glare. The visibility of an object is
determined by many factors apart from background luminance.
Mere reduction of background luminance by an auto dipper in
a particular situation need not necessarily result in clear
perception of the objects on the road through visual
information. The physical dimensions of the object, the
luminance reaching the object, it's reflectance factor, its
colour contrast, its time constancy, its movement in space,
etc. determine the nature and quantum of visual information
available. The actual perception is dependent on the
physical condition and the perception method of the viewer.
The headlight systems of the vehicle, including the number
and type of lamps, their alignment and their efficiency, all
play a vital role in influencing the visibility of objects
on the road.
An auto dipper could play a crucial role
in shifting the headlights from driving beam to meeting beam
and vice versa. This will improve visibility by minimizing
glare, a major cause of momentary loss of vision. The
realization of the ultimate goal of total road safety
through creating ideal visibility conditions is dependent on
efforts in all other related areas mentioned above.
WHAT IS THE
AMERICAN EXPERIENCE AS STATED BY NHTSA
Extracts from
the reports:
DEPARTMENT OF TRANSPORTATION
National Highway Traffic Safety Administration
49 CFR Part 571
[Docket No. 01-8885; Notice 01]
RIN 2127-AH81
Glare from Headlamps and other Front Mounted Lamps
Federal Motor Vehicle Safety Standard No. 108;
Lamps, Reflective Devices, and Associated Equipment
1. Background
At the turn of the Twentieth century,
with the automobile industry still in its infancy, some
vehicles began to be equipped with kerosene lamps for use as
night time road illumination. Within ten years, vehicle
manufacturers began to use electric headlamps on vehicles.
In 1914, members of the Society of Automotive Engineers (SAE)
who were involved in the design and specification of motor
vehicle lighting began to express their first concerns about
the glare produced by these headlamps. Since that time, SAE
members, who were primarily lighting and optical engineers,
and human factors scientists have sought various ways to
reduce glare for other drivers and, at the same time,
improve the roadway illumination for drivers. Over the
years, hundreds of variations of headlamps and unique
technologies have been implemented on motor vehicles. For
example, there were many variants of glare reducing devices,
before lower and upper beams became the norm, that were
achieved by a mechanical metal shield that was rotated into
place in front of the bulb within the headlamp, typically by
using a driver actuated cable. The effect was to reduce the
emitted light, either direct or reflected, leaving only
light directed away from oncoming drivers. Another example
from about 1929, was General Electric's Tung-Sol Blue-Wite
TM headlamp bulb. It was advertised as providing whiter
light for safer road illumination and added comfort, with
courtesy extended to others. The pale blue color of the
glass, reduced the red content of the light emitted. It was
claimed to be the latest development at the time.
Many reams of paper in the form of formal
research reports, technical papers and meeting minutes of
the World's motor vehicle lighting experts have been
generated over the last nine decades to discuss and tune the
delicate balance between glare and vision at night from
motor vehicle headlamps. These resulted in fairly consistent
decisions among the headlamp researchers and designers
around the world. The resultant beam pattern specifications,
with some subtle variations to accommodate specific roadway
and driving conditions in different countries, have been
incorporated in the lighting regulations of many countries
for many decades.
The balance the agency has maintained
between visibility for the vehicle operator while minimizing
glare for other operators has changed very little since its
federal codification. In 1968, however, light trucks
represented only 10 percent of light vehicle sales and the
most advanced technology used then for lighting was
incandescent filament type sealed beam lamps.
The allowable range of total illumination
performance is fairly wide. There are points in the beam
that require minimum levels of intensity, maximum levels and
some that have both minimums and maximums. Between those
points, there are no requirements. The NHTSA assumption has
been that the nature of headlamp optics tend to make
additional test points not necessary.
The nature and response to glare is
interesting. Whether from headlamps or lamps in your home,
there is a distinction between glare that is disturbing and
glare which is disabling. Essentially, as the intensity of a
light source increases, the impression of the light seen by
observers can range from barely noticeable to disturbing,
and eventually disabling. The particular response of an
individual to any glare source varies based on its
luminance, the intensity of ambient lighting, the distance
and angle between the light source and the observer, the
duration of observation, the age of the observer, and many
other factors. Controlling the intensity of the light source
is one variable among many dozens that affect the glare for
drivers. Controlling the location of the light source,
relative to the observer's line of sight, whether direct
view or indirect view (e.g. from mirrors) is another way.
Quote from the same report:
QUOTE
Some lighting
researchers have suggested that net visibility would be
maximized if all drivers would use only upper beams. While
this may sound incredible, it is based on findings that the
increase in roadway illumination would provide greater
benefit than the high glare from upper beams would take
away. While this is an interesting observation, the driving
experience at night would not be optimized, based on the
volume of complaints of glare with current headlamps. This
raises the issue of whether NHTSA's balance between glare
and roadway illumination should move toward less glare even
if that means less visibility of the roadway environment.
UNQUOTE
All the above point
to the fact that dipping is a solution and if manual dipping
is not dependable then auto dipping is the best solution.
What is an Auto Dipper?
An Auto Dipper is a device capable of
changing over the circuit of head light without the
intervention of the driver given a particular set of
objective road conditions. Its primary aim is to reduce the
dazzle for the observer approaching ahead of the vehicle
while ensuring that the user will not be put to
inconvenience.
THE FUNCTIONAL
REQUIREMENTS ON A DARK ROAD
The basic function of an auto dipper is
to maintain the head lamps in either driving beam or meeting
beam automatically depending on the opposing traffic.
AUTOMATIC DRIVING BEAM
It has to bring into operation the
driving beam if there is no oncoming vehicle. Necessarily
this means the auto dipper must be immune to the signals
from; street lamps, moonlight, road reflectance, solar
radiation during the late dusk and early dawn.
AUTOMATIC DIP BEAM
It has to bring into operation the
meeting beam from both headlights whenever an oncoming
vehicle approaches to within about say 250 meters with its
headlights in driving beam until the vehicle is about to
pass. The auto dipper, after bringing into operation the dip
beam, should logically be capable of continuing the
operation of the headlights in dip beam, if the headlights
of the oncoming vehicle were also shifted to the dip beam.
THE ABILITY OF RESTORING MAIN BEAM IN
THE EVENT OF GLARE
The ability is to restore the driving
beam, when the oncoming vehicle approaches with its head
lights in driving beam position during the safe stopping
sight distance. This ability will result in increasing the
luminance towards the objects in the visual field and will
result in an improved visibility against a high background
luminance. The above said ability will have its relevance
and utility (even if one assumes that all the vehicles are
equipped with an auto dipper) due to the following reasons:
- A wrongly aligned meeting beam can sometimes cause as
much dazzle as is caused by a driving beam.
- The road geometry in a particular situation can be
such that even a properly aligned meeting beam can cause
disability glare.
- The meeting beam's light distribution pattern can get
totally disturbed if proper bulbs are not used.
- The most important factor is that this ability will
bring into operation an auto dipper fitted to an opposing
vehicle at a longitudinal distance which is higher than
the safe stopping sight distance, which ensures that both
vehicles will pass in meeting beam during the safe
stopping sight distance.
THE FUNCTIONAL
REQUIREMENTS ON A LIT ROAD
If the road is lit the visibility of the
user will be aided by the road lighting and his dependence
on the vehicle lighting system will be drastically reduced.
Consequently when the automobile is traveling on a lit road
the auto dipper can maintain the head lamps in dip beam.
This functional behavior will also help the other road users
like cyclists, rickshaws and other non motorized traffic.
In order to ensure the above the auto dipper should be
provided with the capability to assess the road lighting
status. The above ability of assessing the road lighting
status will enable the auto dipper to change it's
operational behavior automatically in accordance with the
road lighting status.
AUTO DIPPER AND
RELATED AREAS
In fact there is an inseparable
inter-relationship between efforts in areas like uniform
head light systems, restrictions on use of non-standardized
headlight, alignment practices a properly designed dip beam
etc to derive full advantage of auto dipping.
Raksha is designed based on the above
conceptual framework and is believed to cater to the actual
road conditions in a way convenient to the user and is
expected to relieve him from the repetitive task of
operating the dipper switch. The auto dipper is not to
replace the human judgment but only to assist the user and
the ultimate control is left with the user.
AUTO DIPPER AND
RELATED AREAS
Head lamps: Automobile head lamps are fitted with Low level DC bulbs of reasonably high wattages of say 60 W to 100 W on either side. Consequently the DC current needed to maintain the lamp output runs into 15 to 25 Ampers depending on the voltage system. For example if a car is fitted with 120/100 W bulbs on either side of the head lamps then the total wattage of Main beams runs into 240W and the total wattage of the DIP beams runs into 200 W and if the voltage system of the car is 12Volts DC then the current runs into 20 Amps plus and if the actual voltage level is high of say 14 volts the current level will go up still further.
The normal head lamp switch provided in the automobile will have the capability to switch this head lamp load but the life of this switch will be limited to about 100 thousand operations since the switch is mechanical and is prone to arching at the time of breaking the contact and is prone to contact welding at the time of making of the contact. Any failure of this part of the switch will call for replacement of the entire combination switch which many users would prefer to avoid for various reasons.
Electromechanical relays have come into the market to offer a solution of enhancing the life of the combination switch and also to reduce the voltage drop in the cable carrying the high DC lamp load . Many models of relays available in the market and a few are shown below.
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