POWER LEDs-
Lighting the Future
K. Vijay Kumar Gupta
Light
Emitting Diodes or ‘LEDs’ as we better know them as, are fast revolutionizing
the lighting scenario.
LEDs aren’t
just for control panels anymore. As a matter of fact, they’ve become a primary
tool for architects, interior designers and lighting professionals who’ve gone
beyond the limits of conventional light sources...and found something better.
If you still think LEDs are only for little red indicator lights on electronic
gizmos, then this article will enlighten you on how LEDs are slowly emerging as
the most sought after light sources in major applications. White LED lighting
has played a major role in this changing scenario. With capabilities to take
place of FTLs/ CFLs, it is fast becoming popular.
LEDs score
over other conventional light sources in many ways.
A Range of Colors:
LED produce high purity colored light that can be mixed to create millions of
colors. Stand-alone colors include violet, blue, cyan, pure green,
yellow-green, yellow (amber), orange, red-orange, red and "white".
Compact Size:
With their small size, LED can be used in places unreachable with conventional
lighting. By producing less heat than conventional lighting, LED-based fixtures
are smaller, resulting in applications that can be safely positioned
inconspicuously
Long Lifespan:
With an expected lifespan of 50,000 to 100,000 hours (approximately 6 to 11
years of 24 / 7 use), LEDs last approximately 50 to 100 times longer than the
typical incandescent bulb.
Robustness:
LEDs are extremely robust - resistant to shock, vibration, mechanical and
thermal stresses, and vandalism. Being fully epoxy sealed, making them
waterproof, and are a suitable option for "hostile" environments like
extreme cold or high humidity. For this reason they are used on cars and
trucks, in airplane cockpits, even in space.
Safety: The low
operating voltage of LEDs eliminates sparks and qualify for UL low-wattage
certification. Reduced weight cuts down on equipment and injuries, and long
lifespan reduces need for maintenance in high, hot and hazardous environments.
With battery back up systems, LED traffic signals, EXIT signs and other forms
of signal lighting continue to operate during power outages. In addition,
increased visibility and immediate illumination enable motorists to respond
faster in emergency situations. Light emitted by LED lights is UV light free
unlike light emitted by halogens. These lamps do not contain mercury unlike the
fluorescent tubes.
Power Efficient :
Since LEDs run on low current and low voltage and efficiently convert
electricity into light, they require less energy than conventional light
sources. While LEDs emit 100% of their energy as visible light, incandescent
bulbs waste 90% or more of their energy in light blocked by the colored lens or
filter. For example, blue LEDs are 20 times more efficient than color-filtered
incandescent bulbs and red LEDs are 3 times more efficient. So LEDs score over
other sources whenever an application as required by FTL or CFLs calls for
filters or red, green, amber as in traffic signs and automobile lamps, in power
panels and even in medical application as blue light for baby incubators and
dental cement curing.
Negligible response time:
100-1000 times faster response in switching on which can render driving safer
when used as automobile brake lamps.
Design Flexibility:
LEDs can be arranged in virtually an infinite number of configurations to
create new design solutions. In addition LED are readily controllable and
easily programmed to make subtle changes in color, color temperature and
qualities of light. Unlike FTLs and CFLs, LED lights can be dimmed or
brightened to suit need of the occasion.
Styling Possibilities:
By manipulating color and brightness, LED lamps can control environments and
moods, complement product appearance and features, and enhance product
placement. They create different looks in retail and commercial environments -
from traditional to contemporary to futuristic. LED lights do not flicker too.
Operational voltage:
LED lamps can operate on low-voltage DC voltages. So they stand ideally matched
for automobiles, solar panels, UPS, emergency lamps and many other similar
applications. This avoids expensive inverter circuits.
Low Maintenance:
LEDs are rarely replaced, which saves on labor and puts an end to unsightly
burned out bulbs or tubes and saves cost on maintenance personnel.
Color Rendering Index (CRI): It is interesting to note that in a psycho-physical test s
have shown that a low-CRI-LED light source was preferred to a high-CRI halogen
or incandescent light sources. CRI of a light source is a measure of the degree
to which the perceived object colors illuminated by a test source conform to
those of the same objects illuminated by a standard source such as an
incandescent light source. CRI also determines the quality of reading light.
The CRI of Incandescents as well as halogens is 98. The CRI value attained by
RGB LEDs of 465, 525 and 640nm is 23, which goes up to 70 when Red (640nm) is changed
to Amber (615). For phosphor coated White LEDs the CRI is 82. Thanks to this
fact, now more efficient white LEDs are being developed.
It used to be that white
LED was possible only by "rainbow" groups of three LEDs -- red,
green, and blue -- and controlling the current to each to yield an overall
white light. Now a blue indium gallium nitride inside chip with a phosphor
coating is used to create the wave shift necessary to emit white light from a
single diode. This process is much less expensive for the amount of light
generated. Amount of phosphor decides the shade of white- Cool white which is
the brightest shade has the least amount of phosphor followed by pale white and
incandescent white in decreasing order of brightness.
A 1.2 watt white
LED light luster is as bright as a 20-watt incandescent lamp (bright enough to
read by).
As
white LEDs have a very steep Current vs Voltage curve, a small change in
voltage (say 0.2V) will change current by more than 20mA which could lead to
the LED burnout. Hence, it is imperative to have controls in place to achieve
consistent results. Various controls are underpower, resistance, constant
voltage control and constant current control.
Underpower
is where LEDs are connected to a battery which does not have enough voltage to
drive them to normal current levels. There is no power loss but the LEDs are
dimly lit as they cannot draw full power.
The
most common way to control power in LEDs is to use a resistor in series with
the LED.
Constant
voltage power supply is aided by small, light weighted and reliable power
supplies whose supply voltage is matched to the LED driving voltage. This
technique is also the most energy efficient driveConstant current regulator is
more complicated than a constant voltage power supply but it eliminates
matching the voltages. But it requires at least 3 volts in excess to LED
voltage.
Imagine never
having to change lamps, which consume too little electricity to notice. LED
lights work well for rooms with TV or radio because they do not generate radio
frequency interference as some compact fluorescent lamps do. They produce
little heat, and can operate in hot or cold environments. LED white Lamps do
not emit UV Rays that could be carcinogenic.
The biggest
limitation to LED lamp application for common residential use is the cost of
manufacturing due to still-limited production runs. Manufacturers claim
production will increase considerably by 2008, further lowering prices. The
input power that a LED can take is so limited because LEDs chip is hardly 0.3mm
to 1mm square. Main effort is focussed on producing bigger LED structures that
retain the efficiency of smaller chips.
Applications
of Power LEDs is limited by imagination alone.
Kwality’s
EVERON Power LEDs fall in this lighting category of LEDs. Available in various
packages of Superflux or
internationally popular ‘Piranha’, and PLCC-SMD LEDs more popularly
called TOP LEDs, these EVERON LED Lights have very high thermal efficiency with
extremely short thermal path paving way for cooler operation of the chip at
currents as high as 70-100mA. Conventional LEDs cannot operate these currents .
The kwality’s EVERON series of 1Watt white LEDs can take 350mA input and replace
multiple LEDs. EVERON series is also available as 1.2w & 2.4wattt clusters
of 23mm diameter with kwality’s proprietary thermal spreader technology. EVERON
Power white lamps with focussed beam assembly are also slated to be released
soon. All EVERON lamps are available with optional compact constant current
regulators at low cost.
LED lamps
could consume less than a quarter of the electricity that GLS lighting does,
and last about twenty times as long. Until recently, though, the price of an
LED lighting system was too high for most residential use. With sales rising
and prices steadily decreasing, it's been said that whoever makes the best
white LED will open a goldmine.
LED-It’s
the future of light.
The author is Managing Director
of Kwality Photonics Private Limited ,and
is the Member of the CSIR – Expert Committee on New Millennium Indian
Technology Leadership Initiative on Development of White LEDs for General
Lighting and past president ELCINA.
Captions for the figures
Fig1 : Kwality’s EVERON PLCC_SMD
LEDs can be Single color, Bi-Color and even Tri-color and have wide 120 degree
View Angle.
Fig2: Kwality’s EVERON Superflux
LEDs combine the beam-shaping lens with High Power
Fig3: Kwality EVERON PLCC- SMD
Clusters are available in 1.2W and 2.4W ratings in all colors and white.