The centerpiece of atypical LED is a diode that is chip mounted in a reflector cup and held in place by a mild steel  lead frame connected to a pair of electrical wires. The entire arrangement is then encapsulatd in epoxy. The diode chip is generally about 0.25 mm square. when current flows across the junction of two different materials, light is produced frim within the solid crystal chip. The shape, or width, of the emitted light beam is determined by a variety of factors: the shape of the reflector cup, the size of the LED chip, the shape of the epoxy lens and the distance between the LED chip and the epoxy lens.The composition of the materials determines the wavelength and colour of light.In additio to visible wavelengths. LEDa are also available in infare wavelengths. from 830nm to 940nm.
the definitin of 'life' varies from industry to industry. the useful life for a semiconductor is defined as the calculated time for the light level to decline to 50% of its original value. For the lighting industry, the average life of a particular lamp type is the point where 50% of the lamps in a representative group have burned out. The life of anaLED depends on its packaging configuraion, drive current, and operating environment. A high ambient temperature greatly shortens an LEDs life.
Additionally, LEDs now cover the entire light spectrum, including red, yellow, orange, yellow, green , blue and white.