You don't need real lights for ennemies !
Real lights are expensive if you don't use an AAA engine using very otpimised deferred lightning !

Even on AAA games ennemies don't cast real lights , some tricks are used :
- old method : weel done alpha light sprite
- faster : light sprite with projection shader like in Doom 3
(your game is top down view : projection shader would do
the job greatly)
With that no more need to break level in too much polygons !

Juts ideas !