Laylatul Qadr is the calm, peaceful night. And our Prophet Muhammad PBUH has given these signs for us to determine the night.
Laylatul-Qadr (Arabic: لیلة القدر), The Night of Power, is the holiest night in the Islamic date-book. Muslims trust that on this night, the Quran was sent down from the paradise to the Earth. The correct date of this night is obscure, however, happens on one of the last ten odd evenings of Ramadan (21st, 23rd, 25th, 27th, or 29th). As indicated by Islamic custom, Muslims who remain upon this blessed night revering God will have every one of their wrongdoings pardoned. Moreover, they will be allowed the same number of good deeds just as they had generated consistently for one thousand months (83.3 years).