Time Delay on Emergency Lights keeps egress illumination on briefly after power returns—bridging the gap while fluorescent and HID sources (metal halide, mercury vapor, high‑pressure sodium) warm up to full brightness. Without a short hold‑on timer, corridors and large rooms can remain dim just when people expect them to be bright again.
Last updated: October 2025
Overview—What “Time Delay” Actually Does
Time Delay (also called a hold‑on or retransfer delay) keeps battery‑powered emergency lights on for a short, preset interval after normal utility power returns. Instead of shutting off the moment power comes back, the emergency luminaires continue operating—maintaining code‑required egress illumination until the building’s normal lighting is fully usable.
That grace period is crucial in facilities that rely on gas‑discharge lighting (fluorescent or HID), which can take several minutes to re‑strike and reach full output. During that warm‑up, without a time delay, exit paths may not meet required light levels.
Why You Need It After Power Is Restored
- Bridges the “dim window”: Fluorescent and HID sources can be unusably dim immediately after a power blip or outage. Time delay prevents a sudden drop in egress lighting when people think the emergency is over.
- Supports life‑safety intent: UL 924 and NFPA 101 focus on maintaining continuous, adequate illumination of the egress path. A short hold‑on makes that continuous hand‑off practical when normal lights lag.
- Improves crowd movement: In arenas, gyms, warehouses, or assembly spaces, delayed shutoff avoids hesitation and congestion as occupants re‑orient.
- Reduces nuisance toggling: Minor power “hiccups” won’t cause emergency lights to flicker off/on if a short delay filters out the noise.
How the Time‑Delay Function Works
Inside a compliant emergency light, the charger/transfer circuitry senses a return of AC power. With time delay enabled, the unit stays in emergency mode for the selected interval (commonly 5, 10, or 15 minutes) before cleanly transferring back to normal operation. Most units provide a status LED and a push‑to‑test so you can confirm operation.
Tip: If your facility has generator retransfer or an automatic transfer switch (ATS), use the time‑delay function to ride through any brief dips or sequencing steps while sources synchronize.
Where Time‑Delay Emergency Lights Make the Most Sense
- Warehouses & manufacturing with metal halide or HPS high‑bay lighting.
- Gymnasiums & arenas that still rely on legacy HID fixtures or older fluorescents.
- Cold environments (coolers, vestibules) where fluorescent warm‑up is slower.
- Large open areas and tall ceilings where full ambient light is critical for wayfinding and safety.
For more context on sizing and light levels in these environments, see the High‑Lumen Emergency Lights Guide.
How to Choose the Right Delay (5/10/15 minutes)
Most manufacturers offer 5, 10, and 15‑minute presets. Use the shortest delay that reliably spans your normal‑lighting warm‑up. Consider lamp type, ambient temperature, and whether you’re on generator power during re‑transfer.
| Normal Lighting Type | Typical Warm‑Up / Re‑strike | Suggested Time‑Delay |
|---|---|---|
| Modern LED | Instant‑on | 0–5 min (often not needed) |
| Fluorescent (T5/T8) | ~1–3 min (longer in cold) | 5–10 min |
| Metal Halide | ~5–10 min to full | 10–15 min |
| High‑Pressure Sodium | ~3–5 min | 5–10 min |
| Mercury Vapor (legacy) | Several minutes | 10–15 min |
- Walk the egress path during a test; note when ambient reaches satisfactory levels.
- Confirm generator/ATS sequencing; your delay should outlast the final transfer step.
- Balance safety and battery life—don’t overshoot by more than you need.
Not sure how long your battery will last with added hold‑on time? Our Battery Backup Buyer’s Guide explains runtimes and battery types so you can plan conservatively.
Wiring, Setup & Testing
- Enable the delay: Many units ship with time delay disabled; set the jumper, dial, or interface per the spec label.
- Record your setting: Note the chosen interval (e.g., 10 min) on the inside of the door or maintenance log.
- Push‑to‑test: After AC return, verify that heads stay on for the programmed time and then transfer cleanly.
- Self‑test options: Consider self‑diagnostics for automatic monthly and annual tests—especially in large facilities.
For mounting best practices, see Mount It Right: Installation Options.
Code & Compliance Notes
Time delay is not a separate “listing”; it’s a feature on a UL 924–listed emergency luminaire that helps you maintain the intent of NFPA 101 and coordinate with NEC 700 transfer behavior. Your Authority Having Jurisdiction (AHJ) may ask how you confirm that egress illumination remains continuous and adequate during retransfer and normal‑light warm‑up.
- Documented testing: Keep a simple commissioning note: chosen delay, date, locations, and results of the push‑to‑test walk.
- Coordination: If a central inverter or generator is used, coordinate the time delay with the ATS or control system so there’s no gap.
- Don’t hide deficiencies: Time delay complements code compliance—it doesn’t replace inadequate normal lighting or spacing of emergency heads.
For deeper code background (remote heads, UL 924/NFPA 101/NEC 700 roles), see Remote Head Code Requirements.
Models & Options That Commonly Offer Time Delay
The time‑delay feature is frequently available on multiple emergency light families. Look for option codes on the spec sheet or a dedicated “time delay” switch/dip setting.
- Steel Emergency Lights—durable housings for industrial or high‑traffic areas.
- Wet Location Emergency Lights—sealed for hose‑down areas or outdoor egress points.
- High‑Lumen Emergency Lights—better throw and spacing for big volumes.
- Self‑Testing Emergency Lights—automate required functional checks.
- Thermoplastic Emergency Lights—economical workhorses for back‑of‑house.
Resources
Helpful Reading
Note: internal blog links in this article are capped to stay within best‑practice limits for topical focus.
FAQ
Does time delay keep both emergency lights and exit signs on?
Time delay is typically an option on emergency lights. Combination exit/emergency units may offer it; standalone exit signs usually do not need it because the egress path relies on the ambient general lighting to reach full brightness.
Do facilities with all‑LED normal lighting still need time delay?
Often no—LED is instant‑on. However, in buildings with generators, complex ATS sequences, or mixed lamp types, a short 5‑minute delay can smooth out nuisance toggles.
Will a longer delay hurt my batteries?
It uses more of the battery’s stored energy during retransfer, but it does not damage a healthy pack. Choose the shortest interval that reliably maintains safe egress until normal lights are truly usable.
Is time delay the same as transfer delay or retransfer delay?
It’s related. “Transfer” usually refers to switching to emergency mode when power fails; “retransfer delay” or “hold‑on” keeps emergency mode active briefly after power returns.
How do I prove compliance to my AHJ?
Document your setting and a simple walk test showing continuous egress illumination from outage through retransfer and normal‑light warm‑up. Include the spec sheet in your submittal.
Where can I get products with time delay?
Start with the Emergency Lights collection and filter by options. Look for “time delay” or similar in the spec sheet or options list.