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Automatic vehicle lighting

Automation doesn't stop you thinking

The rapid development of sensor technology allows car manufacturers to produce increasingly automated cars, but they can’t think and they can’t ‘see’ what you can see.

Variable speed wipers that come on when it rains and lights that come on when it gets dark are now commonplace while we're also starting to see headlights that can switch between dipped and main beam automatically and cars that brake themselves to avoid, or reduce the severity of a crash.

These systems may help to prevent accidents but it's important to remember that the driver remains responsible for the vehicle's progress and safety at all times.

Automation can help reduce driver workload in some situations but is not a substitute for the driver and does not mean that the driver can stop thinking.

Automatic headlights

The sensors for automatic headlights rely on ambient light level rather than on vision and visibility as perceived by drivers so they will not always get it right. Heavy rain or fog during the day can reduce driver vision and vehicle visibility to dangerous levels but ambient light levels may remain sufficiently high to prevent automated lights from coming on.

A survey of 27,662 AA Members found that overall 9% of drivers on the road rely entirely on the car to decide when the headlights come on.1 That means potentially almost 1 in 10 vehicles invisible to other drivers in fog or heavy rain during the day.

Delayed reaction

Automatic lights might take a little time to react to changing ambient light conditions too, so for example, if you drive into a tunnel it's best to switch lights on manually rather than wait and hope that the system will react in time.



There seems to be some confusion over the correct use of sidelights too.

According to The Highway Code the only situation in which you are permitted to drive with sidelights alone is at night on a road which has lit street lighting. Headlights must otherwise be used at night or during the day when visibility is seriously reduced.

Nevetheless almost a quarter (25%) of the drivers in our AA-Populus survey said that they drive with sidelights only when visibility is poor during the day and use headlights at night.1

AA advice is that headlights should be used at all times when driving at night and during the day when visibility is seriously reduced.

Daytime running lights (DRL)

Most new cars registered since February 2011 are fitted with dedicated daytime running lights to the front. Bright enough that they can be seen clearly in daylight, these are too bright to be used at night so will go off automatically when headlights are switched on.

Don't rely solely on DRL when visibility is seriously reduced during the day. DRL are only fitted to the front so your car will be unlit and virtually invisible from behind.


Waiting in a queue

The Highway Code says that you must not use any lights in a way which would dazzle or cause discomfort to other road users and yet in a survey of 24,351 AA Members more than a quarter of drivers admit to keeping their foot on the brake when stationary in a queue of traffic – 17% put the transmission in neutral but keep their foot on the brake and 15% keep the car in gear and their foot on the brake.2

Modern brake lights, particularly high-mounted central brake lights can be dazzling to look at for the driver of a car close behind in a queue.

The Highway Code addresses this issue and says that in stationary queues of traffic, you should apply the parking brake and, once the following traffic has stopped, take your foot off the foot brake to deactivate the brake lights and minimise glare to road users behind until the traffic moves again.

The Highway Code and vehicle lighting
You must
  • Use sidelights between sunset and sunrise (113).
  • Use headlights at night except on a road with lit street lighting (113).
  • Use headlights when visibility is seriously reduced (226).
You must not
  • Use any lights in a way which would cause dazzle or discomfort to other road users (114).
  • Use front or rear fog lights unless visibility is seriously reduced (226).
  • Use hazard warning lights while driving or being towed unless on a motorway or unrestricted dual carriageway to warn drivers behind of a hazard or obstruction ahead (116).
You should
  • Apply the parking brake and take your foot off the footbrake in a stationary queue once following traffic has stopped (114).
  • Use dipped headlights at night in built-up areas or in dull daytime weather to ensure you can be seen (115).
  • Keep headlights dipped when overtaking until you are level with the other vehicle and only use main beam if this would not dazzle oncoming road users (115).
You may
  • Use front or rear fog lights in addition to headlights when visibility is reduced but you must switch them off when visibility improves (226).


Check your lights

Cars with only one headlight are a common sight on our roads – 49% of respondents in the December 2013 AA-Populus survey agreed with the statement, "There seem to be many more cars this year with only one headlight".3

You can check the operation of all lights every couple of weeks by walking around the car – you might need an assistant to check brake light operation – but it's even easier to take advantage of reflections in other vehicles, shop fronts or walls. You'll find that most journeys provide opportunity to check lights, front and rear.

Getting flashed?

Notwithstanding the fact that The Highway Code (110) says that drivers should only flash headlights to let other road users know that they're there, if you find other drivers flashing you a lot then it would certainly be worth checking your lights – maybe there's a headlight or brake light that's not working?


(Page updated 10 October 2016)

1 AA-Populus motoring panel survey of 27,662 AA Members between 13 and 20 October 2015.

2 AA-Populus motoring panel survey of 24,351 AA Members between 21 February and 3 March 2014.

3 AA-Populus motoring panel survey of 17,629 AA Members between 12 and 17 December 2013.