Are photo luminescent or tritium phosphor exit signs acceptable?
The tritium phosphor exit signs have their own internal light source and can be accepted on the same basis as an internally illuminated exit sign. Because the light is produced by a radioactive source, no connection is required to a source of normal power or emergency power. This type of sign is useful where there is no readily available source of electrical power but they have the disadvantage that they have to be replaced after a number of years (specified in the listing). The photo luminescent signs do not produce their own light but only store light generated from another source. The length of time that these signs will release a useful amount of light and remain visible depends on the intensity and duration of the initial exposure. For this reason these signs can only be accepted on the same basis as externally illuminated exit signs. An external source of illumination will always be required and, where exit signs require emergency power, this source of external illumination must
