Headlight dazzle: Shining a light on safety concerns

Approximate read time: 10 minutes

1. Dazzled drivers

In response to a petition launched during the 2019–24 parliament which attracted 14,107 signatures, the previous Conservative government said it intended to commission independent research into headlights dazzling oncoming drivers.^[1] The Labour government subsequently commissioned research in October 2024 and a report is expected in summer 2025.^[2]

Evidence suggests that drivers whose cars have LED (light-emitting diode) headlights may experience safety benefits, including faster reaction times, and LED bulbs are more energy efficient than classic halogen bulbs.^[3] However, oncoming drivers report being negatively affected by brighter beams.

The RAC and Baroness Hayter of Kentish Town (Labour) are among those to have called for the government to commission independent research on the issue of headlight glare.^[4] The College of Optometrists has also reported a rise in patients experiencing problems with headlight glare.^[5]

An RAC survey of 1,866 drivers in December 2024 found 95% thought at least some car headlights were too bright. Of those drivers:^[6]

• 53% had been “temporarily blinded” while driving
• 79% said they find it hard to tell when some vehicles are indicating
• 77% found it difficult to judge the position of oncoming vehicles on the road
• 25% avoid driving at night due to headlight dazzle; a further 22% would like to drive less at night due to dazzle, but had no option other than driving (for example for work)

Some drivers reported suffering eye pain, fatigue and headaches after experiencing dazzle on the road.

2. Potential causes

The RAC survey asked participants if the problem was increasing: 61% said it was. Campaigners pointed to the increase in LED and to a lesser extent xenon headlights, a decrease in previously industry-standard halogen bulbs, and the positioning of headlights.^[7] A study published in the Frontiers in Psychology journal also found that headlight glare particularly affected people with cataracts.^[8]

John Bullough, director at the Light and Health Research Center at Mount Sinai hospital in New York, has pointed to three key issues potentially increasing dazzle:^[9]

• an increase in taller cars, including SUVs and pickups, which are more likely to have lights that shine in the eyes of pedestrians and drivers of lower cars
• incorrect positioning of headlights, sometimes knocked out of position over time
• bluer toned LED headlights (halogen bulbs tend to be on the red/yellow side of the ‘white’ part of the colour spectrum)

Mark Rea, a light scientist also at Mount Sinai hospital, explained that headlights are measured in lumens, a unit devised to assess how light impacts a central part of the eye.^[10] That part of the eye is more sensitive to higher-wavelength, redder light than lower-wavelength, bluer light. Therefore, bluer lights will have to feel significantly brighter before they register as equal in lumens.

Halogen bulbs also provide a more diffuse light than LEDs.^[11] This means LED lights can seem even brighter as a directional beam in contrast to the surrounding darkness.

3. Can too-bright headlights pass an MOT?

Some issues with headlights may be picked up during an MOT (‘Ministry of Transport’ roadworthiness, safety and emissions test). Headlights should be inspected for road dirt, which could refract light in unintended directions, as well as the angle of the beam.^[12]

How bright a headlight appears is also affected by its housing. Halogen headlights use reflectors to create beam patterns, while LED lights use projectors.^[13] LED bulbs used in halogen bulb housings can emit significantly more glare, causing problems if inappropriate bulbs are used to replace existing bulbs during the lifetime of a vehicle.

A halogen headlamp bulb replaced with an LED bulb would be an MOT failure, assuming the MOT tester recognised that it was an aftermarket part, and the part was in place at the time of the MOT. However, drivers can replace a halogen bulb and its housing with a complete LED unit.^[14]

Technology magazine ARS Technica has described bulbs being sold online without appropriate safety warnings, and stated that beam alignment can be overlooked, causing glare for other drivers.^[15] Car community websites have cautioned readers against buying ‘off-brand’ LED bulbs from online marketplace sellers, which can be more likely to have differences in current between the car and the bulb causing flickering.^[16]

As well as MOT requirements, the Road Vehicles Lighting Regulations 1989 and the highway code set out the legal framework for vehicle lighting.^[17] The regulations set wattage and intensity levels, while the highway code states that drivers “must not use any lights in a way which would dazzle or cause discomfort to other road users”.

4. Collisions

The Department for Transport records how many times each year a police officer has noted ‘dazzling headlights’ as a factor contributing to an accident.^[18] The most recent data is for 2023. Not every road traffic accident is attended by police, and causes are not always known or recorded. Over a decade, the data shows the highest number of collisions in 2013 at 369, and the lowest in 2020 at 196. In 2020 and 2021 the number of cars on the road was affected by national Covid-19 lockdowns.

Table 1. Number of collisions where ‘dazzling headlights’ was noted as a contributory factor

(Department for Transport, ‘Reported road collisions, vehicles and casualties tables for Great Britain’, 19 December 2024)

5. The road ahead

In its response to the earlier petition in March 2024, the previous government said it raised the issue of dazzling headlights with the United Nations Economic Commission for Europe (UNECE) expert group on lighting.^[19] UNECE hosts a world forum for the harmonization of vehicle regulation.^[20] Proposals to amend headlamp aiming rules were agreed in April 2023. The forum also agreed that new vehicles should have mandatory automatic headlight levelling. This would correct the aim of the headlights based on the loading of the vehicle, for example when a heavy load in the boot or the back seat changed the angle of the car. Transitional provisions are in place with “tighter tolerances” coming into effect in September 2027.

The previous government set out its intention to commission further research on 15 April 2024 in response to a written question:

While there are clear safety, security and economic benefits associated with the use of LED lighting, the scientific evidence base on its adverse effects is less advanced. The government is committed to improving the evidence base to ensure we understand the effects more fully before making further policy interventions.^[21]

The Labour government has confirmed that research is currently being conducted by independent transport consultancy and research company Transport Research Laboratory.^[22] The research is expected to be published in summer 2025.^[23] The government said “it will include real-world assessment of glare on a broad range of road types and scenarios including country roads”.

In February 2025 Transport Secretary Heidi Alexander told BBC Breakfast that she had experienced the issues herself as a driver.^[24] She said, “I do accept that being able to see on the roads and not being dazzled is absolutely critical for road safety”. Ms Alexander also highlighted that the government was working on a new road safety strategy.

6. Read more

For information on light pollution, read the House of Lords Library briefing ‘Noise and light pollution: What’s the harm?’ (17 December 2024).

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Cover image by Pavel S on Pexels.