Omaha daily bee. (Omaha [Neb.]) 187?-1922, 1911-03-19
THE EYE OF THE MOTOR CAR
Importance Of Sufficient Power in the
Headlight.
OARELEssNEss PROvEs OOsTLY
Three Principal Points to ne Con-
sidered by Ovvners-Best Method
OF Lighting the Road


WY
Few motoring experiences are more un-
pleasant than driving car equipped with
defective headlights along a strange road
on a dark night. The imperfect iliumina-
ton seems to define rather than to pene-
trate the surrounding blacSness. and there
is never absent from the motorists mind
the feeling that some unknown obstacle
may lie hidden in the obscurity ahead OF
him. While the actual danger I'm such
case may not be very great It is real and.
seeing that a motor car Is too valuable a
piece Of property to be exposed to unneces-
sary risks, the motorist, II he is well ad-
vised will not begrudge a little attention
devoted to his lamps to insure that op-
ticaiiy and I'm other respects they are all
that they should be-
Because II has no complicated parts and
calls for little care or manipulation, the
common tendency is to take the lamp for
granted and to regard the lighting prob
lem as a generation problem exclusively.
This Is doubly a mistake. In the first
place. whether electricity or gas be the
preferred illuminant, the most efficient
generating equipment will fail Of its pur-
pose II the construction Of the lamp which
It feeds be faulty In the second place,
badly designed lamps are commoner than
Is generally supposed. and many car
owner Is under the impression that his
lamps are not large enough when the real
trouble Is that they are inefficient.
The three principal points which must be
considered in connection with lamp eff
cheney are: "a The brilliancy or illumi-
mating power Of the flame or filament; Co
the consumption of gas or electricity; CD
the suitability of the optical devices en-
ployed to throw the light where it can do
most good. We shall consider these in the
order named and then pass on to one or
two other points which are worth looking
to, although their Importance is by com
parison secondary.
All physical quantities are for the pur-
poses of comparison estimated by means
of unit quantity of their own kind Thus
an area is measured in terms of some
standard area such as a square foot, and
| In the same way the intensity of a source
i Of illumination is measured by the Intensity
/ of the light from a standard candle made
OF either sperm or paraffine and Weighing
one-sixth OF a pound. For instance, the
intrinsic brilliancy Of the sun is equal to
900 candles per square inch. that of an
incandescent carbon filament to between
$50 and 200 candles and that of an acetylene
flame to between IS and 100 candles per
square inch OF surface in each case also.
Candle Power.
The candle power OF the unreflected
flame or filament of a headlight should
not be less than fifteen nor greater than
twenty. with acetylene as the illuminant
this will call for the delivery at most
OF z cubic feet OF gas per lamp per hour.
Where a gas tank is used charge of
100 cubic feet should thus be sufficient to
maintain two headlights in operation for
about seventy hours. The corresponding
consumption OF carbide where the acety-
lene is generated the car, would be
about twenty-five pounds for the same
, period and service. II in either case the
actual figures are in excess Of these, the
light is unnecessarily brilliant or the
burner is dirty or defective, or the gas
is being delivered at too great a pressure.
} II the lighting equipment is electrical and
tungsten or tantalum bulbs are employed
J the consumption OF electrical energy should
not exceed twenty-five watts per lamp.
The older the filament the greater the
cost, electrically, per candle power per
! hour
Since a flame projects its rays impartially
In all directions the amount OF iliumina-
tion produced in a given direction di-
minishes rapidly with the distance If we
imagine a source Of light to be placed at
the center of a sphere OF one foot radius,
the surface of that sphere will intercept
all the rays and each point on It will
receive a definite amount of illumination.
Now suppose the radius Of the sphere to
be doubled. It's surface will be increased
fourfold. and, therefore each point on II
will only receive a quarter of the light Il
did before. II the radius be trebled the
illumination at point on the sphere will
be ninth, and so on. the amount of Hgh,
intercepted by given area diminishing as
the square OF its distance from the center
of illumination. The degree OF illumination
produced by a standard candle at dis
lance OF one foot is known as q candle
foot.
Lenses and Renect0rn.
The purpose of the lenses and reflectors
with which lamp is fitted is to defect
the divergent rays from the flame or fila
ment and concentrate them In a parallel
beam. If the source OF illumination were
mathematical point. it would be possible
to direct every ray parallel TO every Other
ray In practice, however. inasmuch as q
flame or flament is not dimensionless, q
reflector which would be accurate for ons
point of It is inaccurate for another. In
choosing a lamp, Il Is, therefore well to
avoid one in which the area OF the reflector
is small for given the size OF the flame
the larger the surface at which its rayl
are reflected the less, relatively, will be-
the distortion OF the beam, due to the fac
that the center Of illumination is not !
; point. Another objection to the use Of I
: small mirror is that the reflected rays
; when their directions are Irregular, inter
, sect each other, the result being that tn,
brightness OF the projected beam varie,
abruptly from point to point.
The range OF lamp is the distance
at which the beam thrown by II may b,
! considered TO be practically effective. Al
a measure OF It. # Is convenient to TAX,
the distance along the center of the bean
at which the intensity OF the illumination
Is Just equal TO one-tenth OF a candle foot
In some comparative lamp trials recent,
made I'm England there was an astonish
ingly wide divergence with different lamp
in this particular, results coming out al
the way from thirty to 900 feet. humble
OF lamps under twenty candle-power 4
which the range lay between eighty and 10
feet were marked as very good.
| Other things eoual a rnodarafa ,,F.t.-,