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LED TECHNOLOGIES
LED technology is often heralded as the future of lighting – and for good reason. LEDs are easy to produce, generate very little heat, and are super energy efficient, using only one-eighth of the power of traditional bulbs and less than half that of fluorescent lights.
A light-emitting diode (LED) is a semi conduct light source. LEDs are used as indicator lamps in many devices and are increasingly used for other lighting. Introduced as a practical electronic component in 1962, early LEDs emitted low-intensity red light, but modern versions are available across the visible, ultraviolet and infrared wavelengths, with very high brightness.
An LED is often small in area (less than 1 mm2), and integrated optical components may be used to shape its radiation pattern. LEDs present many advantages over incandescent light sources including lower energy consumption, longer lifetime, improved robustness, smaller size, faster switching, and greater durability and reliability. LEDs powerful enough for room lighting are relatively expensive and require more precise current and heat management than compact fluorescent lamp sources of comparable output.
Typical indicator LEDs are designed to operate with no more than 30–60 mW of electrical power. Around 1999, Philips Lumileds introduced power LEDs capable of continuous use at one W. These LEDs used much larger semiconductor die sizes to handle the large power inputs. Also, the semiconductor dies were mounted onto metal slugs to allow for heat removal from the LED die.
Practical general lighting needs high-power LEDs, of one watt or more. Typical operating currents for such devices begin at 350 mA.
Solid state devices such as LEDs are subject to very limited wear and tear if operated at low currents and at low temperatures. Many of the LEDs made in the 1970s and 1980s are still in service today. Typical lifetimes quoted are 25,000 to 100,000 hours but heat and current settings can extend or shorten this time significantly. Like other lighting devices, LED performance is temperature dependent. Most manufacturers’ published ratings of LEDs are for an operating temperature of 25 °C.
The most common symptom of LED failure is the gradual lowering of light output and loss of efficiency. Sudden failures, although rare, can occur as well.
With the development of high-power LEDs the devices are subjected to higher junction temperatures and higher current densities than traditional devices. This causes stress on the material and may cause early light-output degradation. To quantitatively classify lifetime in a standardized manner it has been suggested to use the terms L75 and L50 which is the time it will take a given LED to reach 75% and 50% light output respectively.