Civil Engineering Reference
In-Depth Information
Other types of centralized systems use existing wiring to conduct signals to actuators
mounted inside fluorescent luminaires. Another type sends control signals through
wireless radio transmission to receivers mounted in ballast modules.
Almost all the controls just discussed are applicable to both new and existing build-
ings.
Lamp Efficacy and Characteristics
In most applications for a water treatment facility, lamps can be divided into several
categories: incandescent, fluorescent, and high-intensity discharge (mercury vapor,
metal halide, high-pressure sodium, and low-pressure sodium). The basic characteris-
tics of such lamps are shown in Table 30-5. In this discussion of lighting, the term
efficacy
is used to describe lamp light output divided by power input (lumens / watt).
The term
efficiency
is used in reference to luminaires and is the ratio of the light
emitted by the luminaire divided by the light emitted by the lamp.
Incandescent Lamps
Incandescent lamps have the poorest efficacy but are popular
because the fixture and lamp are inexpensive. In addition, no ballast is required to
modify the characteristics of the power supply.
Fluorescent Lamps
The fluorescent lamp is the most common light source in water
plants. Unlike the incandescent lamp, the fluorescent lamp requires a ballast to strike
the electric arc in the tube initially and to maintain the proper voltage and current to
the lamp to maintain an arc. Proper ballast selection is important to optimum light
output, lamp life, and overall efficiency.
Typical lamp sizes range from 40 to 125 W. The efficacy of a lamp increases with
lamp length [from 4 to 8 ft (1.2 to 2.4 m)]. The reduced-wattage fluorescent lamps
introduced since the mid-1990s use 10 to 20 percent less wattage than conventional
fluorescent lamps.
The cool white and warm white lamps provide very acceptable color and energy
efficacy ratings in most locations. New types of fluorescent lamps can produce color
that is similar to the incandescent lamps or daylight but at lower efficacy. Several
dimming technologies are available for fluorescent lamps. Some provide full-range
dimming; others permit limited dimming only but require no modification for existing
fixtures and ballasts.
Fluorescent lamp life is rated according to the number of operating hours per start—
for example, 20,000 hours at 3 hours of operation per start. The greater the number
of hours operated per start, the greater the lamp life. Because fluorescent lamp life
ratings have increased, the number of starts is less important. If a space is to be
unoccupied for more than a few minutes, lamps should be turned off.
High-Intensity Discharge Lamps
High-intensity discharge
(HID) is the expression
commonly used to describe mercury vapor, metal halide, high-pressure sodium, and
low-pressure sodium lamps. Each requires a few minutes (2 to 15) to reach full output.
In addition, if lamp power is lost or turned off, the arc tube must cool to a given
temperature before the arc can be restruck and light produced. Up to 15 minutes or
more may be required for metal halide lamps.
A mercury vapor lamp produces light when the electrical current passes through a
small amount of mercury vapor. The lamp consists of two glass envelopes: an inner
envelope where the arc is struck and an outer or protective envelope. The lamp requires
