Verified answer

They are part of a story arc. Blackest night was basically a zombie event where brightest day was the epilogue to blackest night.

They only became lanterns for awhile.

Brightest Day is about,"Once dead, 12 heroes and villains were resurrected by a white light expelled deep from within the center of the Earth. Deemed a miracle by many and a sign of the apocalypse by others, the reasons behind their rebirths remain a mystery. But it will not be a mystery for long."

Blackest Night is about friends who have died and became black laturns.