This guide explains how photoluminescent exit signs and tritium (self-luminous) exit signs work, where each excels, and how to keep them compliant—so you stay inspection-ready under UL 924, NFPA 101, and local code. Written in plain English for facility managers, contractors, AHJs, and building owners.
Last updated: August 2025
At-a-Glance (When to Use Each)
Photoluminescent
- “Glow-in-the-dark” pigments absorb ambient light, then re-emit in darkness.
- No wiring or batteries; needs continuous light during occupancy.
- Great for well-lit corridors/stairwells, schools, offices, LEED projects.
Tritium (Self-Luminous)
- Sealed tritium gas excites phosphors to glow 24/7 with no charging light.
- Ideal for persistently dark, remote, or hard-to-service areas.
- 10–20-year life; regulated recycling at end-of-life.
Quick Pick
- Choose Photoluminescent where lights stay on during occupancy.
- Choose Tritium where light isn’t guaranteed or access is difficult.
Introduction
When it comes to emergency preparedness, exit signs guide occupants to safety during outages, fires, or other emergencies. Two energy-free options—photoluminescent and tritium (self-luminous) exit signs—offer battery-free solutions with distinct advantages.
This guide explains how each sign type works, when to use them, and what to consider for installation and code compliance. Whether you’re upgrading a facility or retrofitting an older building, understanding the differences helps you choose the right solution.
What Are Photoluminescent Exit Signs?
Photoluminescent exit signs are “glow-in-the-dark” signs that absorb ambient light and emit it when it’s dark. They rely on photoluminescent pigments, typically strontium aluminate, to store light energy.
When mounted in well-lit areas, they remain charged and compliant with NFPA 101 and UL 924 standards for 90-minute visibility. Unlike electrical signs, they require no power, wiring, or batteries.
Eco-Friendly Bonus: Photoluminescent signs contain no toxic materials and can support LEED goals for sustainable buildings.
Browse Photoluminescent Exit Signs for energy-free options, including the popular Green Aluminum Glow-in-the-Dark Exit Sign.
Related reading: Learn About Exit Signs (covers UL compliance and types).
Related reading: Comprehensive guide to photoluminescent exit signs (charging light, lifespan, and code basics).
What Are Tritium Exit Signs?
Tritium exit signs are self-luminous signs that glow continuously due to radioactive tritium gas sealed in glass tubes. The gas emits electrons that react with phosphors, creating visible light. This glow requires no charging, no electricity, and no ambient light.
Ideal for total darkness or hard-to-access locations, tritium signs provide constant visibility for 10 to 20 years. After that, they must be recycled through a licensed disposal facility due to their radioactive content.
Important: Tritium is safe when sealed but must be disposed of properly. See Tritium Recycling & Disposal for details.
Explore our Tritium Exit Sign Collection, including the durable 10 & 20-Year Self-Luminous Tritium Exit Sign.
Related reading: Do Tritium Signs Contain Radiation? (explains usage and safety).
Real-World Use Cases
- Photoluminescent Signs: Best for schools, offices, stairwells, and LEED-certified buildings with 24/7 lighting.
- Tritium Signs: Ideal for outdoor enclosures, dark basements, remote structures, or hazardous locations.
Comparison Summary
| Feature | Photoluminescent | Tritium |
|---|---|---|
| Power Required | No | No |
| Charging Source | Ambient light (≥ 5 fc) | Self-contained gas |
| Visibility | 90+ minutes after outage | Always-on (10–20 yrs) |
| Maintenance | Minimal (keep area lit/clean) | Replace after lifespan |
| Eco-Friendly | ✅ No batteries | ♻️ Disposal required |
Exit Sign Colors: Red vs Green
Both photoluminescent and tritium exit signs are available with either red or green lettering (or illumination). The choice often comes down to visibility, aesthetics, or local code preference. Red lettering has been the traditional choice in many U.S. buildings, offering a familiar look and high contrast against light backgrounds. Green lettering is now equally common and is considered highly visible—especially in dark or smoky conditions—because the human eye responds well to green hues in low light.
Photoluminescent Signs: You can choose red photoluminescent exit signs or green photoluminescent exit signs to match your environment. In either case, the glowing photoluminescent material is typically greenish when emitting light. A “red” photoluminescent sign usually means the letters are red on a glowing background, whereas a “green” sign often features glowing green letters on a contrasting background. Both color versions are UL 924-listed and will remain legible for at least 90 minutes during an outage. Be sure to select the appropriate visibility rating (commonly 50 ft or 100 ft) based on your building’s layout so that the sign’s letters are large and bright enough for the distance they need to be seen.
Tritium Signs: Self-luminous tritium exit signs also come in red or green illumination. Here, the lettering color is determined by the phosphor inside the sealed tubes (no external light needed). Green tritium signs tend to appear a bit brighter to our eyes in complete darkness (our night vision is more sensitive to green), while red tritium signs provide the classic EXIT look that some prefer. Functionally, both color options meet the same performance standards, glowing continuously 24/7. When choosing, consider which color offers better contrast against your interior and is favored by your local safety codes (some jurisdictions or industries have specific color conventions, though nationally both are acceptable).
Code Compliance & Fire Regulations
Both types must meet UL 924 and NFPA 101. Always verify local adoption and any additional requirements before specifying.
- New York Fire Code — specific rules on photoluminescent requirements in stairwells.
- California Fire Code — outlines self-luminous sign acceptability and disposal standards.
Conclusion
Both photoluminescent and tritium exit signs provide reliable, power-free illumination. Photoluminescent signs excel in eco-conscious, well-lit environments and have virtually no maintenance. Tritium signs shine in unlit, remote, or rugged spaces and remain consistently visible for over a decade.
Use Photoluminescent Exit Signs in lobbies, offices, and schools where lights are always on. Choose Self-Luminous Tritium Exit Signs in outdoor sheds, tunnels, or vaults where consistent light isn’t guaranteed.
By understanding each option’s strengths and limits, you can deploy the right mix of exit signs to meet code and safety goals—without worrying about power or batteries.
Further reading: Glow-in-the-dark signage guide .