Interior Lighting for Designers

start fluorescent lamps can be dimmed
because voltage is supplied continuously to
the cathodes. When dimmed, the special
ballast maintains the cathode voltage so
that the cathodes remain heated to ensure
proper lamp operation. Because instant-
start and preheat lamp electrodes are turned
off after the lamps are started, they cannot
be dimmed.
Fluorescent lamps cannot be dimmed
all the way to “off.” If they are allowed to dim
too far, a flicker or spiraling light pattern
becomes visible inside the tube.
Many systems dim only 3- and 4-ft
lamps. For optimal performance, different
kinds of lamps (T4, T5, T8, or T12) are not
mixed on the same circuit. It is also advis-
able for all lamps that are controlled by a
single dimmer to be of the same length; dif-
ferent lengths dim at different rates.
Dimming fluorescent lamps that operate
either in a cold atmosphere or in an air-han-
dling luminaire sometimes results in varia-
tions in light output and color, which are
caused by the changes in bulb wall tempera-
ture. The color shift is slight; dimmed lamps
usually appear cooler in color.
Fluorescent lamp life is reduced by dim-
ming systems. Considering that a fluores-
cent lamp consumes up to one hundred
times its cost in energy, a slight loss in lamp
life is offset greatly by the savings achieved
through dimming.

HID Lamps
It is technically possible to dim high-intensity
discharge lamps over a wide range of light
output, but HID dimming ballasts are
uncommon: the long warm-up, restrike
delay, and color shift associated with HID
lamps limit their applications.Multilevelbal-
lasts are more frequently used, allowing the
light output to be changed in steps.
A discernible color shift occurs with
dimmed HID lamps. In mercury lamps, how-

ever, this slight change will be negligible; the

color is already inadequate. Clear metal

halide lamps shift rapidly toward a blue-

green color similar to that of a mercury lamp.

Phosphor-coated metal halide lamps exhibit

the same trend, but less distinctly. HPS

lamps slowly shift toward the yellow-orange

color that is characteristic of LPS lamps.

HID lamps have a shorter life as a result

of dimming. As with fluorescent lamps, the

shorter life is offset by energy savings

achieved through dimming.

Central Lighting Control Systems

Local, single-room systems typically consist

of one control station with switches or

manual sliders that control large amounts of

power. The dimmable wattage is limited only

by the capacity of the system. These local

systems are easily expanded to multiple

rooms and customized to offer many combi-

nations of manual, preset, assigned, and

time-clock control. They can incorporate

energy-reduction controls such as occu-

pancy sensors and photosensors, and can

handle emergency power functions.

Whole-building systems use local or

small modular dimmers, a central computer,

and master control stations to control all of

the luminaires in a home or commercial

building. Many of these systems also oper-

ate other electrical systems, such as motor-

ized shades, fans, air-conditioning, heating,

and audio systems, and they interface easily

with burglar alarms, “smart” building sys-

tems, and other electrical control systems.

In centralized systems, a microproces-

sor assimilates the data, determines the

required change, and initiates action to

complete the change. More sophisticated

processors can respond to a number of com-

plex lighting conditions in the space, collect

power and energy-use data, and supply

summary reports for building management

INTERIOR LIGHTING FOR DESIGNERS