Emergency vehicle lights and scene lighting: how color, brightness and glare affect safety
How to warn drivers without blinding them and light a roadside scene safely
Safety Behind the Wheel Foundation built this guide from Federal Highway Administration (FHWA) guidance and the national traffic control manual, Occupational Safety and Health Administration (OSHA) guidance, an AAA Foundation for Traffic Safety pilot study and published lighting research. Every source is listed at the end.
What warning lights and scene lights do
Two kinds of lighting show up at roadside scenes. Warning lights ride on a vehicle and flash. They help drivers identify a response vehicle and tell them to take care. Scene lights are floodlights, light towers and work lights. They light the area where a crew is working at a controlled incident.
Police, fire, EMS, road agency and towing vehicles all carry warning lights [1]. Trained workplace crews use them too. FHWA says emergency vehicle lights are not traffic control devices. Traffic control devices are the signs, signals and markings that agencies install to guide traffic. Still, drivers lean on warning lights to understand what they are driving toward [1].
The stakes are real. Traffic incidents raise the chance of a secondary crash, which is a new collision caused by the first one. FHWA says incidents threaten both responders and the traveling public [2]. Responder safety is the first of three core goals of traffic incident management. The other two are safe, quick clearance and reliable communication [3].
Roadside service crews face the same risk. In a 2026 AAA Foundation pilot, technicians from one towing organization filled out more than 4,000 daily logs covering over 22,000 service calls. They reported 18 near misses while working at the roadside. About 44% happened in the dark and 33% in daylight [4]. The sample was small, and the authors urged caution. The protections reported most often were cones, emergency vehicle lighting and high visibility apparel [4].
Who decides, who may use them, and which rules apply
FHWA says there is no national rule on what color, brightness, mounting position or flash pattern a warning light should have. That is true whether it sits on a police car, fire truck, ambulance, road crew truck or tow truck [1]. So the choice falls to whoever owns the vehicle. That may be a fire chief, an EMS director, a tow company owner, a road agency manager or a workplace safety lead.
Some rules do exist around the edges. The Manual on Uniform Traffic Control Devices (MUTCD) is the national rulebook for signs, signals and markings. Its temporary traffic control rules list flashing lights on vehicles among the ways to mark a work area and give advance warning [5]. OSHA points readers to the MUTCD for guidance on work zone signs, barricades and flagging [6]. The MUTCD also says workers in the right of way, including emergency responders, must wear high visibility apparel that meets the ANSI/ISEA 107 standard [5]. A 2016 study found that standards for yellow flashing lights in work zones did not say how the lights should be coordinated to guide drivers [7].
Authorized use matters. Rules on which colors a vehicle may show can differ by state and by the vehicle’s job. An agency or business should confirm the rules with its state motor vehicle agency or state highway safety office before it buys. If you are not an authorized responder or fleet, do not add red, blue or other flashing lights to a personal vehicle. Ask your state first.
Buy from professional emergency equipment suppliers, authorized dealers and apparatus manufacturers. Have qualified installers mount the lights. Ask for written specifications, warranty terms and crew training. Public traffic control devices are different. Only the agency in charge may choose, design and install them, and residents should never try to add or change them.
What color and flash research shows
Researchers test warning lights in labs, on test tracks and with scale models. The results help, but they do not settle every question. Several of the studies below used amber beacons or simulated workers, so apply them with care to red and blue lights.
Comparison compiled by Safety Behind the Wheel Foundation
What studies show about warning light features
| Feature | What studies found | Source |
|---|---|---|
| Color | Drivers tend to read red, blue and amber as signs of most to least hazard, in that order. Amber directional lights cause less worry and show drivers where to go. | [1] |
| Height | Flashing lights near a driver’s head height are the easiest to notice. | [1] |
| Flash pattern | Lights that never go fully dark between flashes are less confusing. In lab tests, partial off patterns helped drivers judge how fast they were closing in. | [1, 8] |
| Flash rate | A faster rate (4 flashes per second) felt more urgent than 1 per second in a UK video study. In a night field test, amber beacon detection distance did not differ between the two. | [9, 10] |
| Brightness | Lower brightness is advised for stopped vehicles. Lab work on amber beacons suggested a peak between 750 and 2,000 candela. | [1, 8] |
| Number of lights | Too many lights and mixed patterns can distract and confuse drivers, most of all at night. | [1] |
A candela (cd) is a unit that measures how bright a light looks from a given direction. Brighter is not always better, as the glare section below explains.
Flash rate shows why timing matters. A faster flash can signal urgency [10]. That may suit a vehicle moving through traffic. FHWA advises a calmer rate once the vehicle is parked at the scene [1]. In a simulated work zone with yellow lights, drivers preferred sequential or matched flashing over random flashing during the day. At night, a peak of 25 candela with a sequential pattern worked best for showing drivers the path [7].
Vehicle color is part of the picture too. A 1990 paper in an optometry journal argued that red is poorly detected and that lime yellow stands out better. It also questioned how well flashing lights, strobes, reflective trim and sirens work on their own. The paper noted that fire departments have long used red [11]. It is an older, single author paper. Treat it as a reason to ask questions, not as proof.
Glare: when more light makes the scene less safe
Glare is light that makes it hard to see or uncomfortable to look at. Disability glare is strong enough to hide things near the light. Discomfort glare is unpleasant or distracting but may not block your view.
At a collision scene, a bright vehicle can wash out the people standing beside it. FHWA notes that calmer flash patterns reduce bright, chaotic scenes that sometimes hide responders on foot [1]. It also notes that cutting forward facing lights lowers distraction for drivers approaching from the other direction [1]. On many newer fire trucks, those lights dim on their own once the crew sets the parking brake. Some systems also adjust brightness for day or night [1]. Ask whether your local vehicles do.
There is a point where extra brightness stops helping. In lab tests of amber beacons, reaction times stopped improving once the peak reached about 750 candela in daytime. At night, when glare matters most, drivers’ view of low contrast targets did not drop much until the peak passed about 2,000 candela [8]. Those numbers apply to amber beacons, not to every light.
Lights win attention. Reflective clothing helps drivers find the person. In a night field study, simulated workers wearing reflective vests were seen from the greatest distance under every light setting tested [9].
Scene lighting: light the work, not the drivers’ eyes
Scene lighting lets crews see patients, hazards and tools. It also makes crews easier to see. The goal is enough light for the task and no more.
- Aim lights down and toward the work area, not at the lanes where drivers approach.
- Keep bright sources from sitting directly behind responders, where they can turn people into silhouettes.
- Use the lowest level that lets the crew work safely.
- Check the view from the approach side before you settle in.
- Recheck after you move a vehicle or raise a light tower.
The MUTCD says flagger stations must be lit when flagging is used at night, except in emergencies. It also says the work area and its approaches may be lit [5]. A crew that directs traffic by hand needs light on the person, not in the oncoming driver’s eyes. A simple check is to have a second person stand where drivers will approach, or drive past slowly, and report what they can see.
A tiered lighting routine from first call to departure
FHWA describes a tiered approach. Lighting is strong while a vehicle responds and calmer once it is on scene [1]. This routine turns that idea into steps. Agencies should fit it to their own written policy.
- While responding, use the full warning package your policy allows. A moving vehicle needs to be noticed from far away.
- On arrival, park where the vehicle helps protect the scene, then set the parking brake. Many newer fire trucks dim their forward facing lights at that point [1]. If yours does not, dim them by hand.
- Move to a calmer flash pattern. Turn off lights that no longer add information. Favor patterns that never go fully dark [1].
- Add scene lighting aimed at the work area and away from approaching lanes. Then check the view from the driver’s side.
- Recheck as conditions change, such as nightfall, rain or backed up traffic. Some systems adjust brightness for ambient light on their own [1].
- Before leaving, return lights to the normal setting. Report any light that failed or seemed to confuse drivers.
Choosing equipment and keeping it working
Before buying, ask the supplier plain questions. Does the light dim on its own? Can patterns be matched across the vehicle? Can you pick a calm pattern for stopped scenes? How bright is it, in candela? Who trains the crews? Lab work suggests two matched amber beacons help drivers judge closing speed better than one [8].
Upkeep is simple but easy to skip. Check the lights at the start of each shift. Look for dead sections, cracked lenses, loose mounts and dirty covers. Look at night too, because a weak section is easy to miss in daylight. Confirm that patterns still match after any repair. Replace parts with the same specifications, since a different part can change brightness or pattern. Keep a short log and fix problems fast.
Comparison compiled by Safety Behind the Wheel Foundation
Common lighting mistakes and better habits
| Common mistake | Why it hurts | Better habit |
|---|---|---|
| Leaving every light on at a stopped scene | Too many lights and patterns confuse drivers [1] | Step down to a calmer pattern |
| Full bright lights facing the other lanes | They distract drivers coming from the other direction [1] | Dim or switch off when parked |
| Mixing many flash patterns | Mixed patterns add confusion [1] | Pick one matched pattern |
| Aiming floodlights toward traffic | Glare can hide people on foot | Aim at the work area and check from the driver’s view |
| Trusting lights alone | Reflective vests were seen from the farthest distance [9] | Wear high visibility apparel [5] |
| Skipping night checks | Weak lights go unnoticed | Walk around the vehicle after dark |
What drivers can do near flashing lights
FHWA describes warning lights ahead as a cue to slow down, move over and be careful [1]. Safety Behind the Wheel Foundation gives drivers the same advice. Near misses happened in daylight as well as in the dark in the AAA pilot, so stay alert on bright days too [4].
- Lift off the gas early and look well ahead for people on foot.
- Move over if it is safe, or slow down if you cannot. State laws differ, so see our guide below.
- Keep your eyes on the path you want to travel, not on the lights.
- If glare bothers you, slow down more and glance toward the right edge of your lane.
- Leave extra space behind the vehicle in front of you.
Technology may help. FHWA’s Next Generation TIM effort highlights smart emergency vehicle lighting and digital alerts. It says smart lighting can give drivers clearer information about an incident. Digital alerts are meant to warn responders about nearby moving traffic [12].
Questions to ask your fire department, tow operator or road agency
If you are a resident, parent, school board member or small employer, your job is to ask, not to fix. Use this list to start a calm conversation.
Start with the local fire chief or tow company manager. For state roads, ask the state transportation department about its traffic incident management program. FHWA says its national training program has trained more than 600,000 responders, so ask whether local crews have taken it [12]. Report concerns by phone or email. Do not walk into an active scene to raise them.
Frequently asked questions
Why do emergency vehicles use different light colors?
No national standard sets warning light colors, so practice varies by agency and state [1]. Drivers tend to read red, blue and amber as signaling the most to least hazard, in that order [1]. Amber flashing beacons also protect service workers in transportation, utility and construction jobs [8]. Rules on who may use which color differ by state. Check with your state motor vehicle agency before you buy.
Is a brighter warning light always better?
No. FHWA advises lower brightness for stopped vehicles [1]. Too many lights and patterns can confuse drivers, and glare can hide people beside the vehicle [1]. In lab tests of amber beacons, reaction times stopped improving once the peak reached about 750 candela in daytime [8]. More light can add glare without adding useful warning.
Why do responders dim or turn off some lights at a scene?
Once a vehicle is parked, drivers no longer need the strongest signal to notice it. They need clear, calm information. FHWA’s tiered approach uses fewer lights and a calmer flash rate on scene [1]. Cutting forward facing lights also lowers distraction for drivers coming from the other direction [1]. Many newer fire trucks dim those lights on their own once the parking brake is set [1].
Can I add flashing lights to my own vehicle?
Rules differ by state, and lights that look like emergency lighting are meant for authorized use. Check with your state motor vehicle agency before adding any flashing light. If your car breaks down, your hazard flashers are the right tool. Our roadside breakdown guide explains what else to do. Never add lights meant for responders to a personal vehicle on your own.
What should I do if flashing lights blind me at night?
Slow down and leave extra space ahead. Glance toward the right edge of your lane so you can keep steering without staring at the lights. Avoid hard braking if someone is close behind you. Move over if it is safe. Expect people on foot near the vehicles, because glare can hide them. If you feel unsafe, slow further and keep going carefully until you are clear.
Who should I contact if scene lighting looks unsafe?
Start with the local fire chief, EMS agency or tow company. For state roads, contact the state transportation department’s traffic incident management program. Ask whether crews have completed national responder training, which FHWA reports has reached more than 600,000 responders [12]. Share what you saw in writing, such as the time, place and what the lights were doing. Do not approach an active scene to make your point.
The bottom line
Recommendation from Safety Behind the Wheel Foundation
Safety Behind the Wheel Foundation urges crews to step down to calm, well aimed lighting once a vehicle stops, and asks drivers to slow down and move over. Warning lights and scene lights save lives when they are used with care. They fail when every light is on at once, aimed at the wrong place, or left at full brightness after the vehicle has stopped. The best habit is simple. Look at the scene the way an approaching driver will.
For crews, that means a tiered routine, regular upkeep and lights chosen with clear questions. For everyone else, it means slowing down, moving over and asking your local agencies how they light their scenes. Calm, steady lighting protects the people working beside the road and the families driving past them.
Related articles
- Move over laws by state: who's protected and what you must do
- Work zone and move over safety: protect road crews, responders and you
- Post crash care: what to do in the first minutes after a crash
- Roadside breakdown safety: what to do when your car breaks down
- Night driving safety: how to see hazards and stop in time after dark
Sources and further reading
- 1Federal Highway Administration (FHWA). Emergency Vehicle Lighting (Next-Generation TIM factsheet, FHWA-HOP-24-053). Published 2024. ops.fhwa.dot.gov/…/fhwahop24053.pdf
- 2Federal Highway Administration (FHWA). Traffic Incident Management. Accessed October 2026. ops.fhwa.dot.gov/tim
- 3Federal Highway Administration (FHWA). Introduction to Traffic Incident Management: Saving Lives, Time, and Money (FHWA-HOP-22-14). Published 2022. ops.fhwa.dot.gov/…/IntroductiontoTIM_v2_508.pdf
- 4AAA Foundation for Traffic Safety. Piloting a Reporting System for Roadside Safety Incidents. Published July 2026. Data year: pilot of about six months (calendar year not stated in the text reviewed). aaafoundation.org/…/202607-AAAFTS-Roadside-Incident-Report…
- 5Federal Highway Administration (FHWA). Manual on Uniform Traffic Control Devices, 11th Edition, Part 6: Temporary Traffic Control. Published December 2023. mutcd.fhwa.dot.gov/pdfs/11th_Edition/part6.pdf
- 6Occupational Safety and Health Administration (OSHA). Highway Work Zones and Signs, Signals, and Barricades – Overview. Accessed October 2026. osha.gov/highway-workzones
- 7Rea MS, Bullough JD, Radetsky LC, Skinner NP, Bierman A. Toward the Development of Standards for Yellow Flashing Lights Used in Work Zones. Lighting Research & Technology 50(4):552-570. PubMed record, published 2016. pubmed.ncbi.nlm.nih.gov/30369834
- 8Rea MS, Bullough JD. Toward Performance Specifications for Flashing Warning Beacons. Transportation Research Part F 43:36-47. PubMed record, published 2016. pubmed.ncbi.nlm.nih.gov/30416367
- 9Kersavage K, Skinner NP, Bullough JD, Garvey PM, Donnell ET, Rea MS. Investigation of flashing and intensity characteristics for vehicle-mounted warning beacons. Accident Analysis & Prevention 119:23-28. PubMed record, published 2018. pubmed.ncbi.nlm.nih.gov/29990610
- 10Turner S, Wylde J, Langham M, Morrow A. Determining optimum flash patterns for emergency service vehicles: an experimental investigation using high definition film. Applied Ergonomics 45(5):1313-1319. PubMed record, published 2013. pubmed.ncbi.nlm.nih.gov/23746746
- 11Solomon SS. Lime-yellow color as related to reduction of serious fire apparatus accidents–the case for visibility in emergency vehicle accident avoidance. Journal of the American Optometric Association 61(11):827-831. PubMed record, published 1990. pubmed.ncbi.nlm.nih.gov/2081824
- 12Federal Highway Administration (FHWA). EDC-7: Next-Generation TIM: Technology for Saving Lives. Updated May 22, 2026. fhwa.dot.gov/…/nextgen_tim.cfm
This article reflects the safety priorities of emergency vehicle visibility and roadside scene safety. It is general education, not legal, medical, insurance or financial advice. Lighting rules differ by state and change over time, so verify details with official sources. For your own situation, contact your local fire chief or tow company, your state motor vehicle agency or highway safety office about lighting rules, and your employer's safety lead for workplace needs. Reviewed October 2026.
Cite this article: Safety Behind the Wheel Foundation. “Emergency vehicle lights and scene lighting: how color, brightness and glare affect safety.” drivewithcare.org, https://drivewithcare.org/emergency-vehicle-warning-lights-scene-lighting/. Reviewed October 2026.
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