Light technologies comparison:
products - general
Inefficient Light Technology
Incandescent bulbs use
a 100-year-old technology that generates light by passing a large
amount of electrical current through a small wire. This wire glows
white-hot (almost) and radiates energy in all directions. A
consequence of this method of generating light is that only 15% of
the energy produced is visible light; the remaining 85% is
dissipated as heat!
Out of the rainbow of
colors that make up white light, you have to filter out all of the
light, except the color you want the lantern to emit (i.e., a blue
lens blocks or filters out all light except blue). In the end,
very little of the energy emitted by the incandescent lamp is seen
by the observer through the colored filter.
above, for filtered interior incandescent bulbs, the
intensity depends on the color. For blue, the filtered
transmission is about 0.4%, for green, about 1%, and for
red, about 1.5%. The rest of the energy is wasted in heat
Compact Fluorescent Lamps
Fragile, Complex and Environmentally Hazardous
lamps (CFLs) were developed as a relatively efficient alternative
to incandescent bulbs and many solar-powered outdoor lighting
products utilize these lamps as their light source.
In short, fluorescent
lamp technology consists of a thin glass tube filled with
argon/mercury vapor. At each end of the tube are metal electrodes
coated with an alkaline-earth oxide that gives off electrons
easily. When a current is passed through the ionized gas between
the electrodes, the fluorescent lamp emits ultraviolet radiation.
The inside surface of the fluorescent tube is coated with
phosphors, typically zinc silicate or magnesium tungstate. These
phosphors absorb the ultraviolet radiation and re-radiate the
energy as visible light. A fluorescent lamp will operate until the
alkaline-earth oxide coating on its electrodes is depleted.
When starting a
fluorescent lamp, the unit requires a "boost" in the form of a
starter and ballast that provide up to four times the operating
voltage in the beginning.
Disadvantages of CFLs:
illumination. Similar to incandescent bulbs, CFLs create
unfocused light, and produce an uneven illumination. To
compensate, systems using fluorescent lamps typically install
reflectors to redistribute the output, which is inefficient and
creates an additional level of complexity and cost to the
consumption. CFLs can consume up to 20 watts, depending on
their application (although the tubes are listed at a lower
wattage, it is important to consider that the driving ballasts
use energy as well). This level of power consumption requires
large, expensive solar modules and associated installation
hardware to generate the required energy. In addition, large
batteries are required for power storage and typical reserves
are less than a week - this doesn't leave enough autonomy to
compensate for seasonal or poor climatic conditions.
Difficult to power
manage. CFLs tend to be either "on" or "off". Although it is
not impossible to adjust the output dynamically, it is a
complicated process. This makes power management difficult,
imprecise, or non-existent, which is a liability for
solar-powered lighting products where the source of power varies
according to seasonal fluctuations and prevailing weather
life. The rated life of typical CFLs is about a year and
products using them require regular maintenance. This increases
the life cycle cost of the product in terms of servicing labor,
storage costs and proper disposal (fluorescent tubes and their
ballasts are considered hazardous materials).
degradation. Manufacturers of CFLs conduct their rated life
and light output calculations under ideal operating conditions
and temperatures that usually do not reflect the actual
environmental conditions. The performance and lifespan of CFLs
is dramatically degraded by extremes in ambient temperature.
Another drawback with CFLs is that they are composed of fragile
glass tubing. If the fixture is impacted with minimal force, the
tube will break and the lamp will cease to operate. Moreover,
the resulting glass fragments are sharp and dangerous.
materials. The EPA in the United States regulates the
disposal of CFLs because of they contain highly toxic mercury.
The ballasts are also regulated under the Toxic Substance
Control Act (TSCA) and Comprehensive Environmental Response
Compensation and Liability Act (CERCLA) because they contain
PCB's and other toxic components.
State-of-the-Art Light Technology
At the heart of a
Light Emitting Diode (LED) lamp is a silicon "chip" about the
size of a grain of salt and made of a special blend of
crystals. When a small electrical current is passed through
the chip it generates light.
LEDs offer a number
of technical advantages over any other type of lighting,
The color of the
light produced by LEDs is dependent on the combination of
crystal materials that comprise the silicon chip. Therefore,
LEDs produce only one color, as needed, for a particular
light application. Almost all the energy required by the LED
is usable as the intended color without the need for
filters. Currently, LEDs are available in white, amber, red,
green and blue output colors.
incandescent bulbs or even fluorescent lamps, almost all of
the energy used by LEDs is converted to light, rather than
examples in the graph above indicate, the luminous
efficiency for an LED ranges from about 5% for blue to
just over 20% for red, and almost no energy is wasted
through heat dissipation.
Furthermore, the shape of the LED package focuses the
light without the need for additional optical
components, making them more efficient and
cost-effective at utilizing the light produced. The
isotropic nature of incandescent or fluorescent lamps
requires external optics to collect the emitted light
and direct it in a usable fashion.
combination of these effects makes LEDs many times
more efficient at producing light than incandescent
bulbs or fluorescent lamps. In addition, the lifetime
of an LED is about 100,000 hours (27 years assuming
the LED is on continuously for 10 hours per day); this
is about 20 times as long as the best incandescent
bulbs (5,000 hours) and twice as long as the best
fluorescent lamps (cold cathode CFLs are rated at
about 50,000 hours).
extremely durable. Vibration or shock easily breaks
the fragile filament in an incandescent bulb and the
glass tubing of a fluorescent lamp. LEDs, on the other
hand, are completely solid-state technology and are
In addition to
being robust, efficient producers of light, LEDs are low
voltage devices that are naturally suited to
solar power . Further, with recent advancements in LED
technology, including increased color choices and brightness
capability, LEDs provide a natural technical synergy for
producing solar-powered LED lighting.