Samir,
I did it as part of my PPL. If I recall correct, you have to do 5 hours of total night flying, in which you must do five take-offs and landings solo (just five circuits around the airfield) and you must have departed the circuit once and rejoined.
The five hours count as full towards your minimum 45 hours for PPL issue. You save some £/$ because you are not applying for a night qualification seperately. This means you can do some night flying in your hour building.