An LED lamp is a light emitting diode (LED) product that is assembled into a lamp for use in lighting fixtures. The higher efficiency and longer lifespan of LED is already revolutionizing the field of illumination. When compared to the conventional incandescent lights and fluorescent lights , LED lights are way ahead in almost every aspects, thanks to the researches in the LED technology.
What is an LED?
An LED is basically a P-N junction Diode. When a light-emitting diode is switched on, electrons are able to recombine with holes within the device, releasing energy in the form of photons. This effect is called electroluminescence and the color of the light (corresponding to the energy of the photon) is determined by the energy band-gap of the semiconductor. This phenomenon invented by the British experimenter H. J. Round led to one of the most important discoveries of last century.
How come LEDs are so better?
Power consumption
LED lamps overshadow all the other lighting systems when comes to area of Power Consumption. The Operating Current of most of the LEDs are in milliamperes(mA) and with a suitable arrangement of numerous Diodes the power consumption can be minimal.
Power Output and efficiency
When it comes to the power output conventional incandescent light bulbs are nowhere near LEDs. Incandescent lamps emit 98% of the energy input as heat.A 100 W light bulb for 230 V operation emits about 1340 lumens, and about 13.4 lm/W whereas modern LED lamps emits about 70 to 100 lm/W. The efficiency of LED lighting fixtures is not affected by shape and size, unlike fluorescent light bulbs or tubes.
On-Off time and cycling
LEDs are ideal for uses subject to frequent on-off cycling, unlike fluorescent lamps that fail faster when cycled often, or HID lamps that require a long time before restarting. A typical LED will achieve full brightness under a microsecond.
Like incandescent lamps and unlike most fluorescent lamps (e.g. tubes
and CFL), LED lights come to full brightness without need for a warm-up
time; the life of fluorescent lighting is also reduced by frequent
switching on and off.
Lifetime
LEDs can have a relatively long useful life. One report estimates 35,000
to 50,000 hours of useful life, though time to complete failure may be
longer.
Fluorescent tubes typically are rated at about 10,000 to 15,000 hours,
depending partly on the conditions of use, and incandescent light bulbs
at 1,000 to 2,000 hours. The
reduced maintenance costs from this extended lifetime, rather than
energy savings, is the primary factor in determining the payback period
for an LED product
Cool light
In contrast to most light sources, LEDs radiate very little heat in the form of IR that can cause damage to sensitive objects or fabrics. Wasted energy is dispersed as heat through the base of the LED.
The light from a fluorescent lamp is not exactly white light although it seems so. But with LEDs natural white light (like sunlight) can be created.
Slow failure
LEDs mostly fail by dimming over time, rather than the abrupt failure of incandescent bulbs
Shock resistance
LEDs, being solid-state components, are difficult to damage with
external shock, unlike fluorescent and incandescent bulbs, which are
fragile.
But it will not be fair not to mention the disadvantages of LED.
- High initial price: LEDs are currently more expensive, price per lumen, on an initial capital cost basis, than most conventional lighting technologies. As of 2010, the cost per thousand lumens (kilolumen) was about $18. The price is expected to reach $2/kilolumen by 2015.The additional expense partially stems from the relatively low lumen output and the drive circuitry and power supplies needed.
- Temperature dependence: LED performance largely depends on the ambient temperature of the operating environment – or "thermal management" properties. Over-driving an LED in high ambient temperatures may result in overheating the LED package, eventually leading to device failure. An adequate heat sink is needed to maintain long life. This is especially important in automotive, medical, and military uses where devices must operate over a wide range of temperatures, which require low failure rates. Toshiba has produced LEDs with an operating temperature range of -40 to 100°C, which suits the LEDs for both indoor and outdoor use in applications such as lamps, ceiling lighting, street lights, and floodlights.
- Voltage sensitivity: LEDs must be supplied with the voltage above the threshold and a current below the rating. This can involve series resistors or current-regulated power supplies.
- Light quality: Most cool-white LEDs have spectra that differ significantly from a black body radiator like the sun or an incandescent light. The spike at 460 nm and dip at 500 nm can cause the color of objects to be perceived differently under cool-white LED illumination than sunlight or incandescent sources, due to metamerism, red surfaces being rendered particularly badly by typical phosphor-based cool-white LEDs. However, the color rendering properties of common fluorescent lamps are often inferior to what is now available in state-of-art white LEDs.
- Area light source: Single LEDs do not approximate a point source of light giving a spherical light distribution, but rather a lambertian distribution. So LEDs are difficult to apply to uses needing a spherical light field, however different fields of light can be manipulated by the application of different optics or "lenses". LEDs cannot provide divergence below a few degrees. In contrast, lasers can emit beams with divergences of 0.2 degrees or less.
- Electrical polarity: Unlike incandescent light bulbs, which illuminate regardless of the electrical polarity, LEDs will only light with correct electrical polarity. To automatically match source polarity to LED devices, rectifiers can be used.
source: Wikipedia
See luminous efficacy for an efficiency chart comparing various technologies.
