What are the requirements for photoluminescent Exit signs?

Any examples are for illustrative purposes only. 

Where an exit sign is required, they may be either externally illuminated or internally illuminated.

Photoluminescent signs are a type of internally illuminated exit sign sometimes used to mark the means of egress, and as such, must meet certain criteria to ensure that they are reliable and readable by occupants of the facility.  Using photoluminescence, light is absorbed from the surroundings onto the sign surface, stored and then re-emitted, making the signs glow when the building is dark.  

NFPA 101 (2012 edition) The Life Safety Code, Section 7.10.7.2 requires that "the face of a photoluminescent sign shall be continually illuminated while the building is occupied.  The illumination levels on the face of the photoluminescent sign shall be in accordance with its listing.  The charging illumination shall be a reliable light source, as determined by the authority having jurisdiction.  The charging light source, shall be of a type specified in the product markings." Per Section 7.10.7.1, internally illuminated signs shall be listed in accordance with ANSI/UL 924, Standard for Emergency Lighting and Power Equipment.

Some jurisdictions require photoluminescent egress path markers, typically in high-rise buildings.  It should be noted that these signs may not meet the requirements of exit signs and are used in addition to, but not in place of exit signs.  

Reference LS.02.01.20 EP38, EP40