Lesson 4/Learning Event 2
Modern development has brought about a radical change in what is
considered good road illumination. The high-intensity beam of light has given way to the principle
of more illumination and lower general intensity. The 32-candlepower lamp is sufficient with a
narrow, high-intensity beam, but with the general floodlighting effect desired today, a larger light
source is necessary. The sealed-beam headlamp has been developed to meet these requirements.
With the increased use of high-powered lamps have come laws enforcing the proper focusing of the
lights and the use of dual-beam headlamps. The dual-beam headlamp is designed so that one
filament will be at the focal point of the reflector, and the other filament will be out of focus
slightly so that the rays will be turned downward. Depressing the beam is accomplished by a
switch that changes the current from one filament to the other.
ELIMINATION OF GLARE
Cause of Glare
Any light source is said to produce glare if it reduces the clarity of vision of anyone looking toward
it. Practically speaking, the blinding or dazzling effect of light is not due to the brilliance of the
light but to the lack of illumination in the immediate vicinity through which the rays are projected.
The headlight, for example, that produces glare on a dark road at night would not produce glare on
a well-lighted street, and in the daytime with the sun shining, it would hardly be noticed. If the
strong light rays can be kept below eye level, the nuisance of glare will be eliminated.
Many tests have been conducted by the Society of Automotive Engineers and by manufacturers to
eliminate headlight glare as much as possible and still have enough light for safe driving. Two
beams are specified to meet these requirements: an upper beam to provide enough light in front of
the vehicle while driving, and a depressed beam to avoid dangerous glare under normal conditions
of passing. The driver is responsible for selecting the proper beam. The maximum and minimum
intensity at important points of both beams are definitely specified and can be checked with the
light intensity or foot-candlemeter.