Glow in the dark signage: Class B and class C photoluminescence explained

Glow in the dark signage plays an essential role in wayfinding within buildings (knowing where you are and where your destination is). Glow in the Dark signs, often described as Photoluminescent signage, is there to lluminate important safety messages in dark environments and emergency situations.

However, not all photoluminescent signs are the same. There are several different classes of material that dictate the strength and duration of luminescence. Developments in codes and standards around photoluminescent signs are now recognised by industry and legislation with Class B and Class C being two categories of these.

How do they compare to each other and what makes them different? We explain in more detail below.



What is photoluminescence?

Photoluminescence describes a material that has been designed to absorb and store light energy so it can effectively ‘glow in the dark’.

There are two different types of photoluminescence – phosphorescence and fluorescence. The former absorbs short wavelength light before slowly emitting it over time as a longer wavelength. The latter describes the process of trapping light and then instantly releasing it as a different wavelength.

The energy needed for photoluminescence can be supplied by natural daylight or artificial light sources. Once light has been stored it will reveal itself when placed in darkness, allowing text and graphical symbols to become illuminated, making it extremely useful in emergency scenarios.


What is Class B photoluminescence?

Class B photoluminescence is a performance classification provided by the Photoluminescent Safety Products Association (PSPA) that rates the luminosity (how much light it emits) of the material.

The PSPA now recommends that Class B is used as the minimum requirement for use in safety way-guidance systems. Class B material meets the PSPA recommendations, ensuring good performance in low light or smoke filled conditions.

This makes it an excellent choice for emergency signage and similar safety equipment that requires illumination in the dark.


What is Class C photoluminescence?

Class C photoluminescence is the next grade up (higher specification) than of Class B. Class C can produce luminance nearly three times greater over Class B.

It's specification is suited to anyone looking for a brigher and longer luminescence than is be provided by Class B.

Class C is suited to higher performance signage that needs to glow for longer periods. Class C will comply with ISO 16069 should that be a requirement for your buildings way-finding signage.


What is the difference between Class B and Class C luminance?

The difference between class B and class C luminance gets determined by the base materials, inks, luminous pigments and quality used during the manufacturing process. The higher grade Class C material can emit a luminance up to 3 times greater than a Class B material (see table below).

In lit conditions, Class B photoluminescent sign materials can often seem slightly "yellower" on the unprinted areas of a sign, with Class C having a "whiter" look to the unprinted material. Turn the lights out and the difference is clear. Class C provides a stronger luminance with slightly "whiter bluey" shade over the "lime green" of a Class B photoluminescent sign material.

Unless your signage needs to conform to specific legislation, it is not always necessary to use a grade of Class-C as the higher performance material would naturally incur additional costs. Every class of photoluminescent sign materials we supply at the UK Safety Store meets the required PSPA standards, with our signs having a 5-year warranty against fading and cracking.


Photoluminescent Class B vs Class C visual comparison

Photoluminescent Class B vs Class C


What are the luminance classification ratings for photoluminescence grades?

Data from the PSPA's website indicates there are 7 classes in total.

Luminance mcd/m2

2 mins

10 mins

30 mins

60 mins

Class A





Class B





Class C





Class D





Class E





Class F





Class G





Examples of photoluminescent safety signs are:

Limited suppliers in the UK are able to supply and print the higher specification Class C photoluminescent material. Typical examples of Fire and Wayfinding signage are:

Glow In The Dark Fire Exit Signs

Glow in the Dark Fire Exit Signs indicates which direction to follow in an emergency scenario. There are many directional varients available for left, right, up and down directions, making it easy to find one that suits the layout of your building.

Glow in the Dark Fire Action Signs

Glow in the Dark Fire Action Signs clearly lists escape procedures to notify Fire Bridgades and escape the building during an emergency situation.

Glow in the Dark Fire Door Signs

Glow in the Dark Fire Door Signs help remind of the importance in keeping Fire Doors Shut or Closed to aid with Fire preventaion, or free from obstructions to allow safe passage during an emergency.

Glow in the Dark Fire Equipment Signs

Glow in the Dark Fire Equipment Signs clearly indicate the use of Fire fighting equipment that may be present in a building, such as how to use a Fire Extingusher or indicating the Fire Alarm.

Glow in the Dark Fire Assembly Signs

Glow in the Dark Fire Assembly Signs can assist with indicating the location of Fire Assembly Points or indicating what building floor level it is.



The PSPA recommends Class B as the minimum requirement for emergency wayfinding signage, and if you need to meet ISO 16069 standards then you should only be using Class C Extra-Glow Wayfinding Signs.