Specification 25 Photoluminescent exit signs
2019: Spec E4.8: 1
To clarify that Specification 25 provides the design and installation details for photoluminescent exit signs.
What is Photoluminescence?
Photoluminescence is the ability of a material to absorb light and UV rays and then re-emit visible light for a period after the source light has been removed. Another term used instead of photoluminescence is ‘long afterglow phosphorescence’ because the only difference between a phosphor, as used on the surface of many electrical lamps, and a photoluminescent material is the time delay between receiving incident radiation and the emission of the useful light. For ordinary phosphors the time delay is normally measured in fractions of a second, whereas with photoluminescent materials the delay ranges from fractions of a second through to hours and even days. It is this feature which makes the material glow for a longer time after normal lighting is removed. The brightness and the time of the useful glow depend on:
- the properties of the photoluminescent material itself;
- the type of light that is being used to ‘charge’ the photoluminescent material;
- the brightness of that charging light; and
- the charging time.
2019: Spec E4.8: 2
To clarify the application of the Specification and relationship with AS/NZS 2293.1.
Requirements for emergency exit signs are contained in AS/NZS 2293.1. Requirements for photoluminescent exit signs are not included in AS/NZS 2293.1.
Therefore, the requirements for photoluminescent exit signs in Specification 25 reference specific parts of the standard with variations.
Specific considerations for photoluminescent exit signs contained within Specification 25 include:
- smoke control systems;
- sign colour;
- size of pictorial elements;
- viewing distances; and
For the purposes of applying AS/NZS 2293.1 for photoluminescent exit signs, Section 5 and Appendix D must be used.
2019: Spec E4.8: 3
A photoluminescent exit sign must—
- be maintained in a continuously charged state by a minimum illumination of 100 lux at the face of the sign by a dedicated light source with a colour temperature not less than 4000 K; and
- in the event of a power failure, continue to provide a minimum luminance of 30 mcd/m2 for not less than 90 minutes; and
- have its performance verified by testing in accordance with ASTM E2073-10, except the activation illumination in clause 8.3 is replaced with 54 lux.
To specify the minimum illumination, luminance and duration for the performance of a photoluminescent exit sign.
The illumination component of Specification 25 is an important factor for the effective operation of photoluminescent exit signs.
S25C3(a) requires the sign to be maintained in a continuously charged state by a minimum illumination of 100 lux at the face of the sign by a dedicated light source with a colour temperature not less than 4000 kelvins. This ensures the conspicuity of the sign and that, in the event of power failure, the photoluminescent material of the sign is charged to the requirements of S25C3(b).
S25C3(b) requires the sign to have a minimum luminance of 30 millicandelas per square metre (mcd/m2) for a minimum duration of 90 minutes in the event of a power failure. This reflects current international practice.
S25C3(c) references ASTM E2073-10 as a testing method to verify the photoluminescent exit sign complies with S25C3(b). The testing method under ASTM E2073-10 requires a 60 minute charge with an input of 10.8 lux at the face of the sign. However, for the purpose of this Specification, this test is varied to require an input of 54 lux at the face of the sign for 60 minutes.
2019: Spec E4.8: 4
Pictorial elements on a photoluminescent exit sign must—
- where the colour white is used, be replaced with a photoluminescent material; and
- be not less than 1.3 times larger than that specified in Table 5.1 of AS/NZS 2293.1; and
- have a border of photoluminescent material that extends not less than 15 mm beyond the pictorial elements.
To ensure the critical elements of the photoluminescent exit sign are visible.
S25C4(a) varies the colours of a standard exit sign comprising a green background with white pictorial elements to allow for application to a photoluminescent exit sign. For a photoluminescent exit sign however, due to the nature of how it functions, it is not practical to include the white component of the sign. Therefore, where white is used on a photoluminescent exit sign, the white colour must be replaced by a photoluminescent material.
In addition to the illumination requirements of S25C3 to ensure a photoluminescent exit sign is visible, S25C4(b) requires pictorial elements be 1.3 times the dimensional sizes specified in AS/NZS 2293.1. This is consistent with international standards.
2019: Spec E4.8: 5
The maximum viewing distance in clause 5.6 of AS/NZS 2293.1 must not be more than 24 m.
To ensure a photoluminescent exit sign is visible.
To ensure a photoluminescent exit sign is visible the maximum viewing distance of a photoluminescent exit sign is restricted to 24 m. Again, this is consistent with international standards.
Smoke control systems
2019: Spec E4.8: 6
To allow photoluminescent exit signs to be installed in all areas, not just where an area is provided with appropriate means for automatically exhausting or excluding smoke.
Within AS/NZS 2293.1, clause5.3 states that externally illuminated exit signs shall be used only in areas that are provided with appropriate means for automatically exhausting or excluding smoke.
However, photoluminescent exit signs are illuminated externally and internally by virtue of the material properties and an exclusion from compliance with clause 5.3 is provided.