I am not sure which Emergency exit lights the OP was talking about. The photoluminescent lights I mentioned was related to Emergency Escape Path marking systems. Since the late 90s most aircraft have been fitted with these. No messing around with wires or batteries and potential failure.

Here is link to the FAA guideline regarding use of photoluminescent lights for Emergency Exit signs (floor proximity emergency escape path marking systems)
http://ntl.bts.gov/lib/000/900/905/968.pdf


Another article from flight safety regarding this.
http://www.flightsafety.org/ccs/ccs_jan-feb04.pdf