Civil Engineering Reference
In-Depth Information
Tungsten halogen lamps are also classified as incandescent lamps; the main
operating characteristic is that the tungsten that evaporates and deposits on the bulb
walls is removed and redeposited on the filament. They have many advantages such
as maintaining the lumen output close to 100 % throughout life, higher color
temperature (3,000 K), higher lamp efficacy (20-25 lm/W), and a life-span equal
to 3,000-4,000 h.
14.3.2 Fluorescent Lamps
Fluorescent lamps require a ballast which provides an initial high-voltage pulse to
start the discharge through a conducting vapor or gas (mercury, argon, krypton,
others). The ballast also limits current flow through the lamp. Basically the ballast
can be an inductor or a high-frequency electronic device. The latter has the
advantages of (1) reducing power consumption of the lighting system by roughly
30 %, thus improving the luminaire efficiency, if used with fluorescent lamps
designed to work at high frequency, tens of kHz instead of 50-60 Hz, and (2) dim-
ming from 25 to 100 %.
The efficiency of the lamp increases with the arc length; this explains why
fluorescent lamps are generally tubular. Typical values are 70-100 lm/W. The
life-span is determined by the rate of loss of the electron-emitting material and it
is also influenced by the number of times the lamps are switched on (typical life-
span is 7,000-12,000 h instead of 1,000-2,000 h for incandescent lamps). The lamp
depreciation factor reaches 90 % after 1,000 h and then slowly decreases to 85 % at
the end of the life-span. The spectrum of the emitted light is modified by the
phosphor coating on the inside of the tube.
Notice that roughly 20 % of input energy is converted to light and 40 % to
infrared, while 40 % is dissipated as heat.
A choice of chromaticity and color rendering (generally 80-90) can be made
depending on the phosphor mix of the lamp.
14.3.3 High-Intensity Discharge Lamps
High-intensity discharge lamps include mercury vapor, metal halide, and
high-pressure sodium lamps. They work in the same way as fluorescent lamps
and require starting devices (ballasts).
Mercury vapor lamps provide good color rendition (50-60), color temperature of
3,300-4,300 K, and good efficiency (35-60 lm/W). When the arc is extinguished, it
cannot be switched on again until the vapor pressure is lowered to a point suitable
for the applied voltage (3-7 min). They have a long life-span (up to 10,000 h) and a
depreciation factor of more than 75 %.
Metal halide lamps have better efficiency (65-85 lm/W), better color rendition
(65), and a color temperature of 4,500 K, thanks to the inclusion of metal
