Civil Engineering Reference
In-Depth Information
additives. The life-span is generally 6,000-7,000 h with a depreciation factor of
more than 75 %.
The high-pressure sodium is the most efficient high-intensity discharge lamp. Its
golden-white color quality is a limiting factor for interior use, but improvement in
color rendition (from 20 to 80) has made it acceptable also for interiors. The color
temperature is around 2,000 K and efficiency is very high, up to 130 lm/W. The life-
span is generally 10,000-15,000 h.
Low-pressure sodium lamps operate as discharge lamps. They need a
special ballast. They have the highest efficiency up to 180 lm/W and higher but
their monochromatic yellow light limits their use. The life-span is generally
10,000-15,000 h.
14.3.4 Light-Emitting Diode Lamps
An LED (light-emitting diode) lamp is a solid-state semiconductor device that
converts electrical energy directly into light. Basically, it includes two regions:
the p-region that contains positive electrical charges and the n-region with negative
electrical charges. When voltage is applied and current begins to flow, the electrons
move across the n-region into the p-region through the n-p junction by releasing
energy. The dispersion of this energy produces photons with visible wavelengths.
An LED driver is always required to convert input power into a current source
which remains constant in spite of the voltage fluctuation; a dimmer regulates the
input power from 20 to 100 %.
LED lamps have good efficiency (up to 100 lm/W and even a little higher), high
color rendition (80-90), and a color temperature of 4,000 K and higher. The life-
span is generally 25,000-50,000 h with a depreciation factor of 85 % at the end of
the life.
14.3.5 Luminaires
With all kinds of lamps, luminaires play an important role in lighting systems.
The efficiency of luminaires is highly dependent on the reflectance of
their interior surfaces (reflectors with silver films may reflect more than
90 % of the incident light), and exterior surfaces such as lenses (with
polarizing materials and deflectors). Typical values range between
60 and 75 %.
