Lesson 4/Learning Event 2
Use of Reflector
A lamp bulb is mounted within a reflector so that the light can be gathered and directed in a
confined beam. The best light beam from a lamp is obtained by the use of a parabolic or bowl-
shaped reflector, which is the type in general use. There is a focal point near the rear of the
parabolic reflector at which the light rays from the lamp are picked up by the polished surface of
the reflector and directed in parallel lines to give a beam with a circular cross section. Any other
position of the lamp will not give as limited a beam, but will tend to scatter the light.
Use of Prismatic Lens
The light beam is distributed over the road by means of a prismatic lens. When a prismatic lens is
fitted to a parabolic reflector, the lens bends the parallel rays from the reflector so that the light is
distributed over the road. The vertical flutes of the lens spread the light rays so that the beam is
flattened, with the edges thrown out toward the side of the highway.
Many combinations of light beams are possible. A combination commonly used is where the beam
from the right headlight is projected high to the right side of the road and low to the left side, and
the beam from the left headlight is projected high to the left side and low to the right side. Some
portions of the beam are deflected lower than other portions because of the design of the lens.
When the right and left beams are not the same, the lenses for right and left headlights are not
interchangeable. These beams combine to give a nearly symmetrical beam for driving. With some
headlights, the left light illuminates the right side of the road, while the right light illuminates the
left side of the road. Both lights together give a symmetrical beam.
Older headlights focus and direct the light. Focusing means bringing the lamp filament to the focal
point of the reflector; aiming means pointing or directing the light properly.