Overview: When Photolum Makes Sense

Photoluminescent (PL) exit signs absorb normal room lighting and re-emit it during a blackout. They cut energy to zero, simplify installation (no wiring, no batteries), and still meet egress rules when properly specified and installed. They’re a strong fit for corridors, stair towers, offices, schools, and retrofits—spaces that are consistently lit while occupied. If a location is routinely dim or dark with occupants present, consider LED (AC + battery) or, where appropriate, self-luminous tritium instead.

What Qualifies as a Photoluminescent Exit Sign

A compliant PL sign is a listed EXIT device whose legend remains legible for the required duration without an internal light source. It relies on a continuous external light source during occupancy to “charge” the face. The product’s packaging and label will indicate UL 924 listing, the legend size/format, and a rated viewing distance (e.g., 50/75/100 ft). If those items are absent, it’s not an acceptable exit sign—no matter what the marketing claims.

UL 924 Listing & Labeling (Non-Negotiable)

UL 924 is the acceptance gate for exit signs in most US jurisdictions. For photoluminescent models, the UL 924 mark certifies minimum luminance, decay performance, legend format (e.g., 6″ letters, 3/4″ stroke), and visibility at a labeled distance after extended darkness. Inspectors typically request evidence of listing, so keep the cut sheet and UL label handy in your submittal set and facility file.

• Legend format: Standard 6″ letters with 3/4″ stroke (unless your local AHJ allows an alternate listed format).
• Labeled viewing distance: Sign must be readable at its rating after 90 minutes of darkness (see Visibility).
• No listing, no go: Decorative “glow” plaques, stickers, or unlisted signs are not substitutes for a UL 924 exit sign.

NFPA 101 Cross-Walk (Life Safety Code)

NFPA 101 requires exit signs to be listed and to remain visible during emergency conditions. It permits photoluminescent (externally illuminated) exit signs if they are lit whenever the building is occupied and conform to their listing. The Code’s performance intent is simple: occupants must always be able to identify the way out, even after normal lighting fails.

• Continuous illumination: PL signs must be lit during occupancy by a reliable source per the listing.
• Legend & placement: Signs must be conspicuous along the egress path; directional indicators are required where the route turns.
• 90 minutes: Visibility must be maintained for at least 1.5 hours after power loss.

IBC/IFC & OSHA—How They Interlock

The IBC/IFC mirror NFPA’s approach: exit signs can be internally illuminated or externally illuminated (photoluminescent) if they are continuously lit during occupancy and listed to UL 924. OSHA recognizes compliance via the adopted life-safety/building codes; practically, if your signs meet UL 924 and the jurisdiction’s code version, you satisfy OSHA expectations as well.

90-Minute Visibility & Viewing Distance Ratings

Every exit sign must remain legible for ≥ 90 minutes after loss of normal power. PL signs do this via stored luminescence. Because their brightness decays over time, the labeled viewing distance (50/75/100 ft) becomes your design guardrail: space signs so the next EXIT is visible before occupants travel beyond the prior sign’s rating.

• 50 ft: Short corridors, stair towers, frequent turns/decision points.
• 75 ft: Longer hallways, midsize lobbies, moderate mounting heights.
• 100 ft: Open areas, warehouses, atriums, auditoriums.

Tip: In a 120-ft hallway, either place two 50-ft signs (staggered) or one 100-ft model with clear sightlines. If sightlines bend, stagger smaller ratings around corners rather than rely on a single long-range unit.

Ambient Light Requirement (~5 fc on the Face)

PL signs must be continually illuminated during occupancy. Most listings call for approximately 5 foot-candles (≈ 54 lux) on the sign face. This is the single biggest success factor: no charging light = no usable glow.

• Design & verify: Use a light meter to confirm ≥ 5 fc on the face after install. Document the readings for your life-safety file.
• Controls: Avoid “dark by sensor” traps—ensure occupancy/daylight controls never leave a PL sign unlit while the area is occupied.
• Emergency feeds: Where required, serve charging illumination from emergency power so signs remain visible through prolonged events.
• Keep faces clean: Dust and film reduce charging and legibility; include periodic wipe-downs in maintenance rounds.

Placement, Spacing & Arrow Conventions

Place exit signs so they are conspicuous from any direction of egress travel. Use arrows (chevrons) wherever the route turns or is not obvious. With PL signs, also think about charging light angles—avoid recesses/soffits that starve the face of illumination. For two-way approaches, use double-face models or back-to-back mounting.

• Height: Follow listing/code (typ. bottom ≥ 80″ AFF) unless a low-level sign is specifically permitted and listed.
• Sightlines: Ensure an occupant always picks up the next EXIT before passing the rated distance of the previous sign.
• Doors & discharge: Mount above exits and along exit access so the path is continuously marked to the public way.

Color & Contrast (Red vs Green, Backgrounds)

Many jurisdictions accept either red or green legends; some require one color. Confirm AHJ preference. Maintain strong contrast with adjacent finishes (avoid near-match backgrounds). If you’re deciding between colors, see our color guide for human-factors considerations; otherwise, match existing signage for route consistency.

Low-Level / Floor-Proximity Use

Some occupancies require low-level exit signs (e.g., certain high-rise stair towers). PL is excellent for this because no wiring is needed at the base of the wall. Verify the model’s listing for floor-proximity use and mount per manufacturer instructions.

Plan Review & AHJ Submittals—What to Show

• UL 924 proof: Include the manufacturer cut sheet showing UL 924 listing and the labeled viewing distance.
• Lighting note: State “≥ 5 fc maintained on PL sign faces during occupancy” and identify fixtures providing charging illumination.
• Locations & arrows: Show each sign and its chevrons; verify spacing against viewing-distance ratings.
• Local amendments: Address any color mandates, low-level signage, pictograms, or high-rise provisions.
• Field checks: Retain light-meter readings and periodic “lights-out” verification in your life-safety log.

Browse UL 924 Photoluminescent Exit Signs Wireless Exit Signs Guide

Operations: Documentation, Inspections & Maintenance

Unlike LED signs, PL units have no batteries to test—but they’re still part of your life-safety program. Keep a simple record of face illuminance (≥ 5 fc), cleaning intervals, and periodic “lights-out” checks that confirm legibility at the rated distance after a simulated outage. If a sign underperforms, verify nearby fixtures first (lamp out? dimmed controls?) before suspecting the sign.

• Cleaning: Wipe faces on a routine schedule; avoid coatings or decals that block charging.
• Relighting: If lighting levels change (fixture swap, controls update), re-verify foot-candles at the sign.
• Replacement: PL signs have long service life; replace if physically degraded or persistently dim despite adequate charging light.

Quick Compliance Checklists

Design / Submittal

• UL 924–listed photoluminescent models specified; labels retained on drawings and cut sheets.
• Viewing distance (50/75/100 ft) matches longest sightline between signs.
• Lighting plan notes ≥ 5 fc on sign faces during occupancy; identify charging fixtures.
• All sign locations and chevrons shown at decision points; low-level units noted (if required).

Installation

• Signs mounted with clear sightlines; no alcove/soffit shadowing the face.
• Double-face or back-to-back mounting for two-way approaches.
• Arrows applied to match actual egress turns; contrast with adjacent finishes verified.

Operations

• Light-meter readings on file (≥ 5 fc at each face); periodic re-checks after lighting changes.
• Faces kept clean; no opacity-adding stickers/films; “lights-out” checks logged.
• Deficiencies corrected (relamp, controls, relocation) to maintain listing conditions.

FAQ

Are glow-in-the-dark exit signs really code-compliant?

Yes—if they are UL 924–listed, installed with continuous charging light during occupancy, and spaced to respect the rated viewing distance. That’s the package inspectors look for.

Do I still need emergency power if I use photoluminescent signs?

You still need code-required emergency lighting, but the signs themselves do not need power. Provide reliable charging light on the faces during occupancy per the sign’s listing.

How do inspectors verify compliance?

Common asks: UL 924 cut sheet/label, face illuminance evidence (≥ 5 fc), locations/chevrons on plans, and a quick “lights-out” look to confirm legibility at the rated distance.

When should I use LED or tritium instead?

Use LED where you need high brightness at long distances or the area is sometimes occupied while dark; use tritium where charging light isn’t guaranteed and wiring is impractical. Otherwise, PL is often the simplest, lowest-TCO option.