what is the difference between an ordinary bulb and an enrgy saver bulb?explain which thing saves enrgy in an enrgy saver?

Compact Fluorescents lamps or bulbs (CFL).have a small
integral ballast made up of electronic components such as Rectifiers (Diodes) Coils
(Inductors), Storage Capacitor and an Integrated Circuits (IC). The electronic circuit
thus produced is used to rectify or change AC (Alternating Current) to DC (Direct
Current) and Voltage Regulator or Booster to produce the high voltage required to ionize
the gas inside the bulb. The ionized or high energy particles then hit the mercury
deposited inside bulb promoting the electrons into a higher orbit.  As the electrons
fall back to a lower orbit characteristic white light is
produced.

As you can imagine producing the electronic
circuit adds substantial cost to manufacturing the bulb. Over time the storage
capacitors degrade and the bulb begins to produce pinkish light. Sometimes the circuit
may fail prematurely.

Disposing of the used or burnt-out
bulbs is an environmental hazard so study the disposal instructions printed on the bulb
package and follow your local code on how to get rid of CFL.