The light bulb has come
full circle.
More than 150 years ago, the incandescent light bulb transformed the way
we live—extending the workday, opening the door for new businesses, and
altering the way we design homes and commercial buildings. While the
technology evolved over the years, the light bulb became an everyday
item, fading into the technological background. Then came the
introduction of smart lighting, a catalyst that has taken the technology
to a level that Edison could never have imagined, piquing the
imagination and fascination of consumers and engineers alike.
Lighting technology has helped to trigger unprecedented energy
consumption and the inevitable development of a power infrastructure to
support a growing range of services. Rising demand and the cost of
energy has led lighting providers to constantly seek new ways of
achieving greater energy efficiency. As a result, the market has become a
patchwork quilt of lighting technologies, serving a shifting assortment
of applications. An examination of each technology’s design, operating
principles, strengths and weaknesses, and applications offers a glimpse
of the role it may play in the future.
Incandescent Lighting
Perhaps the most common form of lighting until recently, incandescent
bulbs produce light by passing electric current through a thin
filament, which becomes white-hot, emitting light over 360 degrees.
Perhaps
the most common form of lighting in North America, the incandescent
bulb has begun to fade from the lighting landscape, driven by its high
energy consumption. Only its low price point has extended its market
presence. Image source: GE Lighting Because of the
light’s omnidirectional emission, the bulb must have reflectors to focus
a large portion of the light on the desired area. Although the
incandescent bulb’s lifespan is short—roughly 1,200 hours—the bulbs
maintain their luminescence well throughout their operating life.
Incandescent bulbs provide a range of color temperatures, but the
three primary options for consumers include soft white (measured at
2,700–3,000 degrees Kelvin), cool white (3,500 K–4,100 K) and daylight
(5,000 K–6,500 K). Incandescent lights turn on almost instantly, and
they are sensitive to voltage inputs, dimming as voltage is reduced.
Incandescent dimming, however, greatly affects power consumption,
operating life and color temperature.
The technology’s Achilles heel lies in its efficiency. An
incandescent light bulb wastes 95% of the energy it generates, consuming
four times more energy than a fluorescent alternative and six times
more than LED bulbs. Incandescent source efficiency—the amount of light
emitted from the bulb—measures about 10 lumens per watt, and its system
efficiency—the amount of light that reaches the target area—is even
lower. This inefficiency has led many parts of the world to pass
legislation phasing out this type of lighting.
The technology’s slide toward extinction, however, may be reversed by
recent design improvements that promise to make the incandescent bulb
more efficient. Researchers at MIT have created a secondary structure
around the incandescent filament made from a specially developed
photonic crystal. The structure captures infrared energy and allows
visible light to pass through. The scientists contend that the new
design achieves an efficiency of 6.6 %—three times the efficiency of a
standard bulb—and they think the bulb’s efficiency could be increased to
40%, which would surpass the performance of both LEDs and compact
fluorescent lights (CFLs).
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Halogen Lamps
Closest in design to the incandescent light bulb, halogen lamps
consist of tungsten filaments, enclosed in a quartz envelope filled with
high-pressure halogen gases, such as iodine and bromine.
The
halogen lamp offers better energy efficiency than the incandescent
bulb. Unfortunately the excessive heat generated by halogen lamps
restricts the applications in which the technology can be used. Image
source: GE Lighting These gases enable the lamp’s filament
to heat to higher temperatures than incandescent bulbs. This causes the
tungsten atoms to evaporate and combine with the halogen gas,
triggering a chemical reaction that redeposits evaporated tungsten back
onto the filament, increasing its life and maintaining the clarity of
the envelope. This produces 12–22 lumens per watt and higher
color temperature than incandescent lamps, with a lifespan of 1,000 hours.
However this technology has a number of shortcomings that must be
considered when included in a design. Because the heat is concentrated
on a smaller envelope surface and the surface is closer to the filament,
halogen lamps get hotter than incandescent bulbs. The high temperature
is essential to their operation, but it can pose burn and fire hazards.
While halogen lamps offer slightly greater luminous efficacy than
traditional incandescent lamps, their performance is still low compared
with alternatives like fluorescent and LED lighting.
On the plus side, halogen lamps do not contain any mercury, and
manufacturers like General Electric (GE) claim the lamps do not contain
any materials that can be classified as hazardous waste. Also, the small
size of halogen lamps permits designers to use the technology in
compact optical systems for projectors and illumination. Perhaps the
greatest advantage of halogen bulbs is the quality of lighting they
provide.
Consequently halogen lamps are used in a variety of applications,
including home and retail lighting, as well as automobile
headlights. But even in these applications, halogen lighting’s days are
numbered.
Fluorescent Lights
A high-efficiency light source, fluorescent lamps provide excellent
illumination for areas where lighting is left on for prolonged periods
of time, and for applications that do not require full brightness.
Raising the bar for performance and energy efficiency, these lamps
generate less heat than incandescent bulbs and convert electricity to
light more efficiently, with luminous efficacy of 40–70 lumens per watt
and life spans of 6,000–15,000 hours. Cost also works in favor of the
technology. Fluorescent lighting offers consumers a nice balance between
up-front cost and payback derived from energy savings.
To generate light, fluorescent bulbs pass electric current between
tungsten electrodes on opposite sides of the lamp through low-pressure
mercury vapor to produce ultraviolet (UV) energy. This energy excites
phosphor materials coating the inside of the bulb, creating visible
light.
Unlike many other light sources, fluorescent lights cannot receive electricity directly. Instead, they require
ballasts to regulate the flow of current. The ballast provides the starting voltage and limits the current that passes through the lamp.
Intended to replace
incandescent light bulbs,
a variant design—CFLs—uses a curved or folded tube to fit into the
space typically allotted for incandescent bulbs. Advances in
phosphor
formulations have improved the perceived color of the light emitted by
CFLs. In fact, some sources see CFLs "soft white" as similar in color to
standard incandescent lamps.
Despite all of these advantages, the light source suffers from significant disadvantages. All fluorescent lamps contain toxic
mercury,
which makes their disposal difficult. Also, the lamps take time to
achieve full brightness, and their diffused light falls short when a
focused beam is required. In addition, fluorescent lights are sensitive
to ambient temperature. As a result, their light output can decline in
cold conditions.
Compact
fluorescent lamps use a curved or folded tube to fit into the space
typically allotted for incandescent bulbs. While advances in phosphor
formulations have improved the perceived color of the light emitted by
CFLs and significant energy efficiency has been achieved, the use of
hazardous materials to produce the bulbs complicates disposal. Image
source: Philips
Poorly designed ballasts also cause a number of problems. Fluorescent
flicker can be irritating to users, and inferior ballasts can create
radio interference that disturbs nearby electronics or cause fires if
they overheat.
While fluorescent lamps provide excellent value for the money, their long-term prospects are not good.
Light-emitting Diodes
Light-emitting diodes, or LEDs, offer the highest luminous efficacy
and lifespan of all residential and commercial lighting options. While
they often come with the highest price tag, LEDs consume 75% less energy
than incandescent bulbs and 40% less than fluorescent lighting. LEDs
also outlive competing technologies, lasting 25 times longer than
incandescent and halogen bulbs, and three times longer than most CFLs.
In addition to energy efficiency, this lighting technology generates
little heat and boasts robust construction, owing to the fact that it
has no filament that can break.
Unlike other lighting options, LEDs are the offspring of the silicon
revolution. Essentially LEDs are simply tiny light bulbs integrated into
an electrical circuit that create light when electrons move through
semiconductor material.
A two-
lead semiconductor light source, an LED is a
p–n junction diode, emitting light when activated by the flow of electrical current. When a
voltage is applied to the leads,
electrons recombine with
electron holes within the device, releasing energy in the form of
light (an effect called
electroluminescence). The energy
band gap
of the semiconductor determines the color of the light, and LED
manufacturers use integrated optical components to shape the bulb’s
radiation pattern.
Often LEDs have a small footprint (some as little as 1 mm2). This
makes the light source an attractive option for designers confronted
with space constraints.
All in all, LEDs offer features that complement a wide variety of applications and enable a range of new features.
Light-emitting
diodes are poised to dominate the home and commercial markets, offering
the highest luminous efficacy and lifespan of all other lighting
options. Advances in the technology have improved light quality and
design aesthetics. Image source:
Raising the IQ Quotient of Lighting Systems
While LED lamps set the bar for energy efficiency, developers of
lighting technology saved the best for last with the introduction of
“smart lighting.” While this term means different things to different
people, common elements of all definitions include unprecedented levels
of energy efficiency and convenience. This metamorphosis has been
enabled by the addition of sensing and communications capabilities to
lighting systems, introducing degrees of control and interactivity that
traditional technology just cannot match.
Harnessing heat and motion sensors, smart lighting can decide when
illumination is required, based on room occupancy. Light sensors can use
natural lighting as a criterion for reducing man-made lighting. By
leveraging multiple sensor streams, smart technology goes one step
further, enabling bulbs and switches to determine when, where and how
much illumination is required. This level of visibility and control
opens the door for automated energy management that can make a real
difference. Simply dimming a lamp 5% to 10% can positively affect power
usage and help to prevent energy waste.
A number of smart LEDs also include wireless communications, such as
Wi-Fi, Z-Wave and Zigbee. With this connectivity, consumers can control
and adjust lighting remotely, using a smartphone or tablet.
The Lighting Revolution
All these advances in lighting promise to revolutionize the way we
live and work. They will add an extra measure of convenience, reduce
energy consumption, and even transform the basic light bulb into a
design element. As impressive as these changes are, they are only just
beginning.
