I think you will find that it is all about ESTABLISHING the ideal fuel/air mix and stabilising the resultant flame quickly. In the case of the afterburning 'long white pointed thing' that until 7 years ago carried passengers in shirt sleeved comfort at Mach 2, the burners were lit at FL 290 for transonic acceleration and lit almost instantly. AND the most inneficient means of ignition, using a swirled arc ignitor was used also, although the fuel flow control was really neat. If anyone is interested I can post some diagrams here to show how it was done with the 'rocket'.
Dude
