Incandescent bulbs create light by passing electricity through a metal filament until it becomes so hot that it glows. Incandescent bulbs release 90% of their energy as heat.
An electric current is driven through a tube containing gases in CFL. This reaction produces ultraviolet light that gets transformed into visible light by the fluorescent coating on the inside of the tube.
LED lighting products like LED Down Light use light emitting diodes to produce light very efficiently. The movement of electrons through a semiconductor material illuminates the tiny light sources we call LEDs. A small amount of heat is released backwards, into a heat sink, in a well-designed product; LEDs are basically cool to the touch.