Lighting Technologies:
Making the Right Choice
KEY POINTS
• Understanding different lighting technologies
can help you make the right choice for
your application.
• Incandescent, fluorescent, HID and LED
technologies produce light differently.
• Lighting technologies can be compared in
terms of efficacy, color quality and operating
life.
• Duke Energy offers rebates on a variety of
lighting technologies and other types of energy
efficiency equipment.
Lighting accounts for up to 45 percent of the total energy
used in commercial buildings. Conventional light sources are
highly inefficient, leading to a substantial amount of research
over the years to improve lighting performance and develop
new technologies. Upgrading your lighting system is a great
way to save energy and reduce operating costs.
INCANDESCENT LIGHTING
Incandescent lamps are the oldest type of electric light
bulb – and still the most commonly used in homes today.
A bulb consists of a screw-in base, which holds two stiff
wires attached to a coiled tungsten filament, and a glass
enclosure that’s filled with argon gas. An electric current
carried through the wires heats the tungsten filament,
causing it to glow. Tungsten is used because of its extremely
high melting point. The argon gas reduces the evaporation
of the tungsten, increasing the life of the bulb.
Halogen lamps are a type of incandescent lighting. A capsule
filled with halogen gas (iodine or bromine) surrounds the
filament to increase bulb efficiency and lifespan. Halogen
bulbs are 25 percent more efficient – and can last up to
three times longer – than traditional incandescent lamps. FLUORESCENT LIGHTING
Fluorescent lights consist of glass tubing coated on the
inside with fluorescent powders known as phosphors.
The tube also contains a low-pressure gas, usually argon,
and a small amount of mercury. Two electrodes (electrical
conductors) are sealed at each end of the tube. A voltage
spike elevates the energy level of the mercury and gases,
creating ultra-violet radiation, which causes the coating to
produce visible light.
Tubular fluorescent lights commonly used in offices and
other commercial and industrial facilities come in T12, T8,
and T5 varieties. The T stands for “tubular,” while the number
refers to the diameter of the lamp in eighths of an inch. For
example, a T8 lamp has a diameter of one inch – or 8/8 of
an inch. Most tubular fluorescent lamps use a bi-pin base
that attaches to the fixture. T12 and T8 lamps use the same
medium bi-pin base, while T5 models are slightly shorter
and have a miniature bi-pin base.
T8 and T5 lamps are more efficient than T12s, due to their
smaller diameter and use of electronic ballasts. T12 lights
primarily use older magnetic ballasts and are being phased
out of production by higher federal performance standards.
A general overview of past and upcoming changes (as
dictated by federal mandates) that will impact availability of
less-efficient fluorescents are spelled out below.
• March 31, 2006 – The last day lighting manufacturers
could incorporate T12 ballasts into new fixtures with fullwattage T12 lamps. The ballasts continue to be produced
for replacement purposes.
• July 1, 2010 – T12 magnetic ballasts ceased to be
manufactured. T12 replacement bulbs continued to be
produced for replacement purposes.
• July 14, 2012 – The majority of T12 bulbs may no longer be
manufactured or imported for replacement purposes.
Specifically, these lamp types will no longer be produced:
• Most 4-foot, linear full-wattage and energy-saving T12 lamps
• All 2-foot, full-wattage and energy-saving U-shaped T12
lamps
• All 75-watt F96T12 and 110-watt F96T12HO lamps
• Most 60-watt F96T12/ES and 95-watt F96T12/ES/HO lamps
• All 4-foot T8 basic-grade 700/SP series lamps rated at
2,800 lumens
• Some 8-foot T8 Slimline single-pin 700/SP series and
8-foot T8 HO RDC-base lamps
Compact fluorescent light bulbs (CFLs) are similar in
operation to tubular fluorescents and are commonly used
in homes and businesses. Screw-base CFLs can be used
with standard sockets, while pin-base models plug directly
into ballasts. The spiral-shaped bulb is the most familiar,
although twin-, triple-, and quad-tube, as well as circular CFL
lamps, are also available.
CFLs use less energy and last much longer than conventional
incandescent bulbs. However, they cost more to purchase
and contain a small amount of mercury sealed within the
glass tubing – an average of 5 milligrams – about the amount
that would cover the tip of a ballpoint pen.
The Environmental Protection Agency (EPA) recommends
that consumers take advantage of local recycling options
for compact fluorescent light bulbs. The EPA is working
with CFL manufacturers and major U.S. retailers to expand
recycling and disposal options. Consumers can contact
their local municipal solid waste agency directly, or go to
www.epa.gov/bulbrecycling or www.earth911.org to identify
local recycling options.
HIGH-INTENSITY DISCHARGE LIGHTING
High-intensity discharge (HID) lamps create light using an
electric arc, or an electrical breakdown of a gas. The lamp
consists of two electrical conductors typically made of
tungsten, and an arc tube filled with gas elements. Voltage
creates the electric arc, which ionizes the gases and allows
a continuous energy transmission to flow between the
conductors.
The arc produces both heat and intense light. Because of
their intense light, HID lamps are typically used for outdoor
lighting or high-ceiling indoor applications. They generally
require a warm-up time of several minutes and a cool-down
time before restriking. Three commonly used HID lamps are
characterized by their light-producing elements – mercury
vapor, metal halide and high-pressure sodium (HPS).
• Mercury Vapor. Mercury vapor is the oldest type of HID
lighting and is used primarily for street lamps. These
lamps cast a very cool, bluish-green white light. Mercury
vapor lamps have a long operating life but a low efficacy
(lumen output per watt input). To save energy, mercury
vapor lamps have been largely replaced by more-efficient
metal halide and high-pressure sodium lamps.
• Metal Halide. Metal halide lamps include both metal halide
(rare earth metal salts) and mercury gases. The addition of
metal halide gases improves efficacy and color rendition. • High-Pressure Sodium. HPS lamps use sodium as the
main light-emitting element, along with a small amount
of mercury. The lamps produce a warm, white light, and
are widely used because of their long lifespan and high
efficacy. LIGHT-EMITTING DIODES
Light-emitting diodes (LEDs) are the latest development
in energy efficient lighting. Technology advances have
increased the potential of LEDs, long used in electronics, in
task lighting and general illumination. Exit signs and traffic
lights are two areas where LEDs have already made great
inroads.
LED lights look more like a computer chip than a traditional
lamp. An LED is a semiconductor diode, which is a small chip
of silicon treated with chemical elements that create a positivenegative interaction. The positive side contains electron
holes, while the negative side contains free electrons. When
connected to a power source, the holes and electrons are
forced together, releasing energy in the form of a light photon. LED lights have a long life (up to 50,000 hours) and are very
durable. Unlike conventional light sources, which emit light
in all directions, LEDs focus light more narrowly. This makes
them especially useful for task lighting. However, standards
and testing for LEDs are still in development for this new
technology. And LED product performance may vary widely.
COMPARING LIGHTING TECHNOLOGIES
Lighting technologies have different operating characteristics,
and some are only suitable for certain applications. However,
a direct comparison of their performance can still be helpful.
The following table provides an overview of the efficacy,
color rendition, and estimated operating lifespan of each
lighting type. Efficacy is measured in lumens per watt. Color
rendition is quantified on a color rendering index (CRI) scale
of 1 to 100, as color rendering index (CRI), where 100 CRI is
equivalent to sunlight.
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Incandescent lights have excellent color rendition, but have the lowest efficacy and lifespan. Fluorescent lights are much
more efficient and have a longer lifespan, but cannot match incandescent lamps in color rendition. HPS lamps compare
favorably to metal halides in efficacy and have a much longer operating life, but possess a very poor color rendition. LED
lights combine a long lifespan and good color rendition but are still catching up in efficiency. As technology advances, the
use of LEDs in a variety of applications should continue to grow.
Lighting Technology Performance Comparison
Technology
Efficacy
(lumens per watt)
Color Rendering Index
(CRI)
Lifespan
(hours)
Incandescent
10 to 17
100
750 to 2,500
Fluorescent
30 to 110
50 to 90
7,000 to 30,000
Metal Halide
70 to 115
70 to 90
5,000 to 20,000
High-Pressure Sodium
50 to 114
25
16,000 to 24,000
LED
40 to 60
70 to 90
35,000 to 50,000
DEVELOPING A LIGHTING STRATEGY
A successful lighting strategy involves much more than just an understanding of available lighting technologies. It includes
proper design and maintenance, as well as the use of energy-saving controls. When considering a comprehensive design,
consult a lighting professional for help in developing a layout that efficiently and effectively meets all the lighting needs of
your facility.
Visit www.duke-energy.com for information on Smart $aver® incentives available for a variety of lighting technologies, as well
as other types of energy efficient equipment.
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