In my fire it was the grow light ballast that overheated and burned through the shelf and onto and through the floor. It was easily identifiable from the other ballasts in use since it was deformed from interior heating and showed signs of case decomposition. The other ballasts in the same area did not have this appearance and were mostly undamaged.
The lighting system components need to be compatible with each other to prevent premature failure. I've included an informational link to how grow light ballasts operate.