High-bay lighting: Opportunities for Mercury reduction and energy efficiency
High-intensity discharge (HID) light sources, such as metal halide and
high-pressure sodium lamps, have long dominated the market for
lighting indoor spaces with high ceilings. These high-bay spaces are
typically found in warehouses, factories, large retail stores, and athletic
facilities. In recent years, however, improvements in fluorescent
lamps and the emergence of new high-intensity fluorescent fixtures
have made fluorescent lighting the most cost-effective choice for
lighting high indoor spaces. These high-intensity fluorescent systems
are more energy efficient than HID solutions and feature lower lumen
depreciation rates, better dimming options, virtually instant start-up
and re-strike, better color rendition, and reduced glare.
The Lamp Choices
HID lamps produce intense light in such a small area that
they are considered "point sources." As a result, they are often
installed in fixtures that direct their light using parabolic
reflectors. Compared with other installations (of the older
T12 fluorescent lamps, for example), an HID installation
may require fewer individual fixtures, which sometimes
allows for lower capital and installation costs. HID lamps are
popular in applications that feature large expanses lit by
distant fixtures, such as indoor and outdoor sports facilities,
factories and warehouses with high ceilings, and street lighting.
Although there are several different kinds of HID lamps,
the most popular types for indoor applications are metal
halide and high-pressure sodium lamps. A key difference
between these two is the type of vaporized metal that constitutes
the gas within the inner glass vessel of the lamp, through
which the electric arc is struck. Of these two types, metal
halides—with their high-quality light, high efficacy, and wide
range of sizes—are more versatile.
Fluorescent lamps emit diffuse light from long glass tubes.
This characteristic of diffusivity has enabled fluorescent fixtures
to dominate the market for lighting commercial,
institutional, and industrial spaces with ceilings less than 15
feet high. In recent years, however, the emergence of more
intense and efficient fluorescent lamps (such as T5s) coupled
with specially designed reflecting fixtures has enabled fluorescent
systems to break through the ceiling-height barrier and
compete directly with HID lamps in indoor applications.
Case Study: New Lighting at
Timken Aerospace
In 1999, Timken Aerospace implemented a lighting
upgrade project for its 142,000 square foot (ft2) manufacturing
facility in Lebanon, New Hampshire. This
facility produces precision ball bearings and requires
high-quality lighting in the manufacturing areas, which
operate continuously (8,760 hours a year). Timken
chose to replace all 543 of the facility's 400-watt metal
halide low-bay light fixtures with 2-ft x 4-ft T5 fixtures
supplied by MetalOptics. The new fixture draws only
232 watts, compared to 455 watts each for the metal
halide fixtures. The project was executed using Timken
personnel, cost a total of $268,000, and qualified for a
rebate of $91,500 from Timken's utility, Granite State
Electric. As a result of this upgrade, Timken Aerospace
has reduced its demand by 120 kilowatts, and is saving
more than a million kilowatt-hours per year and cutting
its annual energy costs by $70,200, resulting in a
payback period of 2.5 years. The facility also benefits
from improved lighting quality and better color.
New Developments:
Occupancy Sensors and Ballasts
New developments give fluorescent fixtures even more
advantages over their HID rivals. One involves occupancy
sensors. With HID lamps, there is a delay of
several minutes between when the light is turned off and
when it can be turned on again. In contrast, the instant
re-strike capabilities of fluorescents make the combination
of fluorescents and occupancy sensors a practical
idea for spaces such as warehouses that are notoriously
over-lit and under-occupied. New line-voltage occupancy
sensors have reduced the installed costs for
occupancy sensors from approximately $150 to $50 per
sensor, making it cost-effective to consider installing one
sensor for each fixture in low-occupancy areas, resulting
in potentially huge energy and cost savings.
The other new development is in the area of ballasts.
Until recently, if an existing HID lamp was wired with
480 volts (V), replacing the lamp with a fluorescent
fixture would require a rewiring job. Now 480-V fluorescent
ballasts are available, making these replacements
much more feasible. In addition, four-lamp ballasts are
now available, reducing the installation costs for fluorescents
compared to the conventional two- or
three-lamp ballasts.
Economic Benefits
High-intensity fluorescent fixtures are more efficient
than most HID fixtures, so they tend to deliver significant
cost savings (Table 1). In addition, fluorescent
fixtures have much better dimming options than HID
lamps, which can translate into significant additional
energy savings. A set of fluorescent lamps can be
dimmed in two ways. First, because most fluorescent
fixtures have multiple lamps, they can be wired with
multiple circuits that can be switched to vary the light
levels. Second, light levels can be dimmed with a
dimming ballast. HID fixtures contain individual
lamps, so they don't offer the first option. They can be
dimmed, but only to about 50 percent of their full
output—and even then the dimming is not linear with
the energy consumed so that in some cases very little
energy is actually saved. In many applications where
dimming is required, the HID lamps are dimmed by the
use of shutters rather than dimming ballasts, which
results in no energy savings at all. For example, school
gymnasiums host several types of activities that require
less light than sporting events. A system of fluorescent
fixtures, each with multiple lamps, could be installed
and wired to allow several different lighting levels,
which would result in huge energy savings at the lower
levels compared to an HID lamp lighting system with
little or no dimming capabilities.
The cost-effectiveness of fluorescent lighting compared
with HID depends on several factors, including lamp
life, lumen depreciation, hours of operation, and electricity
prices. When evaluating costs of different lighting
technologies/fixtures, make sure to compare alternatives
that provide approximately equal amounts of light.
Table 1: Evaluating fluorescent fixture lighting retrofits
To determine whether the cost of retrofitting high-intensity discharge (HID) fixtures with fluorescent fixtures could be recovered in a
reasonable amount of time, we compared a typical HID fixture with two fluorescent retrofit options. Both of the retrofits produced greater net
design pupil lumens than the HID system. Both also yielded simple payback periods of less than three years, based on energy savings alone.
Other Benefits
In addition to lower energy consumption and better
dimming options, the new fluorescent fixtures designed
for high-bay applications have several additional advantages
over similar HID fixtures: lower lumen depreciation
rates, faster start-up and re-strike, better color rendition,
and reduced glare. Not only do these advantages make
fluorescent fixtures more cost-effective in many applications,
they also enable them to provide superior lighting
to the spaces they illuminate. The lamp life for fluorescents
is about the same as for HID lamps, but
fluorescents may have a slight advantage when you factor
in their lower lumen depreciation rates. There may be a
slight convenience advantage for fluorescent fixtures
when it comes to changing lamps: HID lamps need to be
replaced immediately when they fail, but when a fluorescent
lamp fails, several other lamps in the fixture will still
be working.
© Platts, a division of The McGraw Hill Companies, Inc.
|
 |
Downloads
This white paper:
High-bay lighting: Opportunities for Mercury reduction and energy efficiency
(28K) Adobe PDF
The most recent version of Adobe Acrobat Reader
|
back to top