LED's

    LED stands for light-emitting diode. A diode is a device that only conducts electricity in one direction. So all LEDs have a positive and a negetive side that hook up to the positive and negetive side of a battery.
    LEDs are semiconducters of light. This means that they can be controlled easily. Unlike a lazer which has a direct focused beam, LEDs emmit an "incoherent narrow-spectrum light" which means that they are more like a light bulb that elluminates lots of things. This is a type of  electroluminesense, light emitted when electricity is passed through the LED
        The color of an LEDs depends on condition of the materials used.The material can be infrared, visible, or near-ultriviolet.

This is all from wikipedia.