Equipment: Lamps and Gear - Road Lighting: Fundamentals, Technology and Application - page 109

Chapter 10
Equipment: Lamps and Gear
Abstract Since 1932, the low-pressure sodium lamp, the first commercially-used
gas-discharge lamp, has bathed many roads in its yellowish light. Within a few
years it was joined by the high-pressure mercury lamp providing bluish-white light.
The high-pressure sodium lamp, introduced in the late 1960s, with its yellow-white
colour and much higher efficacy, then relatively-quickly replaced the high-pressure
mercury lamps in a large number of applications. There, where lighting levels were
not high and white light was preferred, fluorescent lamps, usually of the compact
type, were sometimes also employed.
In the last part of the last century induction lamps with extremely long lifetimes
were introduced. Around the same time, metal halide lamps with their high-quality
white light became available with lifetimes long enough for them to be employed
for road lighting—high lighting-level road lighting with high quality white light of
high efficacy had become a possibility.
The beginning of this century marked the commercial introduction of a funda-
mentally new type of light source, made of solid-state semiconductor material: the
light-emitting diode, or LED. Today, LEDs have taken over from many gas-discharge
lamps used in road lighting. The principle of operation, the construction and the appli-
cation possibilities of all these light sources are widely different and will be described
in this chapter, as will the auxiliary electrical devices, such as ballasts, igniters and
drivers, needed for their proper functioning. Because of their importance today, extra
attention is given to LED light sources.
Both gas-discharge lamps and solid-state light sources are used for road lighting for
motorized traffic. Figure 10.1 groups the lamps used for this application according
to the technology employed.
In the middle of the past century, the high-pressure mercury (HPM) and the low-
pressure sodium (LPS) were those that were used for road lighting. HPM was used
mainly in built-up areas while LPS was used for motorway lighting 1 . Sometimes,
twin or three-lamp tubular-fluorescent (FL) lamps were also used.
After the introduction of the high-pressure sodium (HPS) lamp in the late 1960s
of the last century, this lamp type replaced most HPM lamps because it has twice the
1 In the United Kingdom, low-pressure sodium lamps were also widely used in built-up areas,
including residential areas.