(a)LED: Led is light emitting diode. It is a pn junction diode, which emits light when gets activated. When a suitable energy is applied , electron combines with the electron holes within the device releasing energy in the form of photons.LED lamps have a lifespan and electrical efficiency which are several times longer than incandescent lamps, and significantly more efficient than most fluorescent lamps.
(b)Insulated Gate Bipolar transistor: It is a transistor device and forms the basic component of all electronic devices. It used to amplify or switch electronic signals and electric power. IGBTs is also used to generate the ( mercury) discharge, which lights up the bulb. It can also fit in a small volume.
(c)Properties of tungsten: Tungsten has a very high melting point , it has low vapor pressure and greatest tensile strength out of all the metals. Because of these properties tungsten is used as filament in incandescent bulb.