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What is UL924 and What’s the Difference Between Self-Luminous and Photoluminescent Exit Signs?

What is UL924? What is the difference between Self-Luminous and Photoluminescent Exti Signs?

All those many exit signs you encounter every day – whether in a retail store, at the office, in a warehouse, at the movies, in a high-rise or low-rise building, whether commercial or residential; the exit signs are listed to Standard UL924. UL924 is the Standard for Safety of Emergency Lighting and Power Equipment published by Underwriters Laboratories, and all exit signs in these different buildings are required by United States building codes to have this UL924-listing.

High-rise Residential Building
An example of a high-rise building

Let’s break down what UL924 means in the realm of exit signs, and then go into the differences between self-luminous and photoluminescent UL924-listed signs.

UL924 Specifications

UL Logo

Life Safety Code: 1011.4 Internally Illuminated exit signs. Electrically powered, self-luminous and photoluminescent exit signs shall be listed and labeled in accordance with UL924… 

NFPA 101

1013.5 Internally illuminated exit signs. Electrically powered, self-luminous and photoluminescent exit signs shall be listed and labeled in accordance with UL924…

IBC International Building Code

Exit signs that legitimately carry their listing to UL924 standards mean they have been extensively tested and listed by a Nationally Recognized Testing Laboratory (NRTL), such as Underwriters Laboratories or ETL – Intertek Testing to meet or exceed the requirements of UL924, which include – among others:

Visibility: The sign must be visible from a viewing distance of 50 feet, 75 feet or 100 feet

Time: Must illuminate for at least 90 minutes after power failure

Exit Lettering: Must be at least 6 inches in height, and the individual letter stroke widths are clearly prescribed

Impact Resistance: Exit signs installed near the floor in low-location must pass an Impact Resistance test

We are going to focus on the two non-electrical type UL924 exit signs as they are the easiest to install and share similarities, but also have some major differences.

Self-Luminous Exit Signs

Self-Luminous (definition): Generating and emitting its own visible light

Merriam webster

Self-luminous UL924 exit signs provide glow through the radioactive tritium gas that the signs are filled with. This makes them easy to install and maintain, as there are no electrical components to wire or batteries to change.

4.52 SELF-LUMINOUS EXIT SIGN – A Sign with an integral legend that is powered continuously by a self-contained energy source other than a battery, such as radioactive tritium gas. Operation of a self-luminous exit sign is independent of external power supplies or other external forms of energy. This definition does not include exit signs dependent upon photoluminescent materials.

Standard UL924

So what are the downsides of self-luminous? Due to their radioactivity, each sign must be registered with the United States Nuclear Regulatory Commission. Further, self-luminous signs only have a 10-20 year lifespan. Per UL924, a self-luminous exit sign shall be marked with the date, expressed in the month and year, on or before which the exit sign is to be replaced. This way, the Authority Having Jurisdiction (AHJ), your building or fire inspector, and your maintenance team can clearly see when the self-luminous signs have reached their expiration date and must get returned to the manufacturer. Once self-luminous exit signs expire, there is a return-fee incurred to dispose of the sign properly by the original manufacturer.

Other than that, they are fairly hassle-free in maintenance, and generally a durable choice for UL924-listed exit signs.

Photoluminescent Exit Signs

Photoluminescence (definition): Having the property of emitting light that continues for a length of time after excitation by visible or invisible light has been removed.

2018 IBC Chapter 2

Photoluminescent UL924 exit signs are made of high-quality, non-radioactive photoluminescent pigments (a.k.a. professional-grade “glow in the dark”). These photoluminescent exit signs can be made in a few different materials to meet different aesthetic tastes and price points.

Photoluminescent UL924 exit signs are also easy to install since they do not require any electrical wiring. They simply need to be installed in a location where LED or fluorescent lights can charge the sign ambiently.

Photoluminescent UL924 exit signs are also unique in the quality that they do not expire. They do not have an expiration date and generally glow for 25 years and beyond. Since they are non-radioactive and non-toxic, should there be a need to replace them, there is no special handling needed and they can be thrown away normally.

Durable, maintenance-free, non-electrical, non-radioactive, easy-to-install, and with no expiration date. It’s easy to see why photoluminescent UL924 exit signs are the preferred choice among building contractors, architects, and code-compliance professionals everywhere.

Review the Differences


  • Self-Luminous – Glows in the Dark via Radioactivity
  • Easy to Install – No Electrical Wiring or Batteries Needed
  • No Maintenance Needed
  • Radioactive – Filled with Tritium Gas
  • Registration – Due to Radioactivity, these signs must be registered with the United States Nuclear Regulatory Commission
  • Limited Lifespan – 10-20 year life
  • Special Disposal Required – Incurs a radioactive waste-fee to dispose of it


  • Photoluminescent – Glows in the Dark via Charge by Ambient Lighting
  • Easy to Install – No Electrical Wiring or Batteries Needed
  • No Maintenance Needed
  • No Expiration – Works for 25 Years and Beyond
  • Non-Radioactive, Non-Toxic – No Special Handling Needed, Simple Disposal

GSA (U.S. General Services Administration) publishes its PBS-P100 Facilities Standards for the Public Buildings Service. P-100 says in Chapter EXIT SIGNS Exit signs must meet the requirements in NFPA 101 and be energy efficient and environmentally friendly products (e.g., light emitting diodes (LED type), photoluminescent type. Tritium exit signs must not be installed.

Photoluminescent signs are the clear choice for UL924-listed exit signs.

PERMALIGHT® Photoluminescent UL924 Exit Signs

American PERMALIGHT® carries a variety of durable, high-quality, UL924-listed photoluminescent exit signs that are perfect for your next emergency exit egress marking installation project. 

PERMALIGHT® PVC Photoluminescent UL-924 listed Exit Signs:

PERMALIGHT® Aluminum Photoluminescent UL924-listed Exit Signs:

PERMALIGHT® Acrylic Photoluminescent UL924-listed Exit Signs:

Contact Us

Have a question about which exit signs will work best for your code-compliant building project? Contact us and a PERMALIGHT® product specialist will guide you to the correct UL924-listed code-compliant exit signs for your emergency exit needs.

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