A Mind Boggling IQ Question

There were 5 persons standing at one side of a bridge on a pitch dark night. All of Them have to cross the bridge. The speeds of all persons are different and they take 1 sec , 3 sec , 6 sec, 8 sec , 12 sec  respectively to cross the bridge. Only 2 persons at most can cross the bridge at a time, that only using the Lamp to see in the dark, without it no one can cross it. This means if 2 persons go with the lamp for the first time then one of them has to return back to handover the lamp. The Lamp will glow for a total of 30 sec, which means all of them has to cross the bridge in 30s . Also when  2 persons are crossing the bridge both the persons will walk at the speed of slower one, which means if  6 sec person is travelling with 12 sec person then it will take 12 sec for both to reach the other end. Also the time during handing over will also be counted as the lamp will glow at that time also which means if 6s and 12s goes , and 6s returns then total time will be 24s. Now, tell in what order and pairs will all of them cross the bridge and in what time ?