When it comes to the illuminance requirements for exit signs, all exit signs need to be evaluated on a level playing field. It's not as though smoke or fire near a doorway will choose to ease up because the exit sign above the door won't be bright enough for people to see. Not to mention, ambient lighting has an adverse effect on exit sign visibility, especially in smoke.
Every exit sign needs to meet the illuminance requirements in UL 924! So why does the NFPA 101 Life Safety Code Means of Egress Panel continue to permit photoluminescent exit signs to be installed above doorways when their illuminance performance is as low as 1/10 of that of electric signs? These signs get listed using a subjective test instead of light measurement methods. It's a failure of the safety system waiting to happen! With that in mind, any building specifier needs to consider the recommendations of NEMA white paper LSD 46-2009 before they "go green" with their doorway exit signs.
By the way, the energy required to “charge” photoluminescent signs and maintain that charge? It exceeds that required for an LED electric sign.