Evening star., 1923-05-06

A good automobile headlight with
well designed lens viii throw
most of its light on the road when
properly adjusted. according to tests
conducted by the bureau of standards
of the Department of Commerce. The
road is brightly lighted for several
hundred feet ahead. yet there is quite
a sharp cutoff line at the level of
the lights. and above that level there
is not sufficient glare to dazzle
driver approaching from the opposite
direction.
When two cars passing each other
are equipped with such lights the use
of DINNERS is neither necessary nor
desirable. The bright light on the
road enables the driver to see be-
Eond the approaching car, but there
shield
Few cars are equipped with really
good lights Most of them become
there are many types of lenses on the
market which fall short of the ideal
requirements.
Types OF Lenses.
The object of using lenses or other
devices. instead of plain glass. is. of
vices have been tried. but not Il
great many can be really called sue
cesSful
The most obvious method to think
OF is to scatter the light. For this
purpose some use ground glass. or
glass otherwise roughened: others
use various types of irregular sur
faces. such as small lenses scattered
all over the lens like the eye of a
NY, circular prism sections, etc.
All OF these methods work by scat
tering the beam. If they make the
glare less intense they also reduce
same effect could be obtained by
using a lamp of lower candlepower.
Use of Screens.
Other attempts consist of cutting
OF a part of the beam by means of
screens. etc. These are all of doubt
ful utility and tend to cut down the
illumination without distributing the
light over the road. Probably the
least sensible of all are those which
attempt 10 hide the filament. The
direct light from this tilament is
usually about twenty candlepower:
whereas the beam from a good re-
fector Is often 10000
The type which first shows a COM
nendable erort TO make a good lens
is the tiuted lens. Such a lens spreads
the beam sideways while Keeping it
concentrated vertically. But it is of
even more Importance that the beam
should not rise above the level of the
lamps. and to bring this condition
about with such Il lens it is necessary
to tilt the headlight down
perhaps the best type of all COM
pines the Huted lens with an arrange
nent of prisms which serve to throw
the light downward. There are many
such types on the market. all differ
ing in details Some of these diff
the distribution of light: others to
avoid infringing some one elses
patent.
In general. a lens of this type an
fn hn Il h,.l Ia.
vertical lines into number of sec
tions. Closer inspection shows the
horizontal lines to be the joining
lines of prisms, while the Vertical
lines are ridges or hollows between
flutes. In some cases, the vertical
lines are absent. the whole outer sur
face being concare.
Several patented types of refiectors
are so designed as to obtain the same
distribution with a plain glass, and
these compare favorably with the
lenses.
Home Adjusting Station.
An adjusting station can easily be
made and can be set up on any level
roadway. 1t consists of screen
about six feet or more in length and
Ave feet high On this screen is
marked horizontal line at the height
of the headlights on the car, and two
vertical lines the same distance apart
as the headlights.
When using lens that require the
headlight to be tilted, another hori-
zontal line should be made on the
screen below the first distance equal
10 the required tilt in inches at
twenty-five feet.
The car should be placed twenty
five feet from the screen. II should
he fully loaded, and the road should
he such that the parts holding the
car wheels and the bottom of tue
screen should be on a level with each
other.
Remove the doors or rims and
lenses from both lamps. Cover one
lamp while working on the other
Adjustment of Lamps.
The lamps should be so adjusted
that their beams are parallel and fall
at the intersection of the horizontal
line with the vertical lines. In cases
where the lens used requires a tilt
the lower horizontal line is used In
other cases the one on a level with
the lamps is used.
Few cars are provided with means
for turning or fitting the lights They
are usually aimed and tilted correctly
when the car Ia made. and future ad-
justment in this respect is usually