What does reverse diode on NPN symbol indicate?
Okay, that is an (unfortunately) typically crappy Chinese datasheet. No ratings at all that I can see on the diode. 

One could begin to harbor doubts about its very existence, despite the usefulness of a diode in that position in certain ballast topologies (those with push-pull dual transistors, it's not in the right position for a general inductive load). 

Here is a proper datasheet for a similar type of part (Fairchild FJP3307D) that actually shows ratings for the diode (Vf = 2.5V maximum at 3A &amp; 25°C). 

They don't say whether the diode is a separate part in the same package (as is done with some IGBTs) or whether it's an integrated feature, but that would be fairly easy to find out from a sacrificial sample or two. 



Here is a schematic of the type of lamp that might benefit from such a component, from this manufacturer: 



When Q1 turns off, then D3 conducts. Similarly when Q2 turns off then D2 conducts. Criss-cross.