Automatic vehicle lighting

The cars are taking over

Your new car may seem like Kitt from Knight Rider, but that doesn’t mean you can stop thinking

Cars are getting more and more automated:

  • Variable speed wipers that come on when it rains.
  • Lights that come on when it gets dark.
  • Headlights that can switch between dipped and main beam automatically.
  • Cars that brake themselves to avoid a crash.

But they can’t think and they can’t see what you can see.

Automation can help reduce your workload as a driver, but it doesn’t mean you can stop thinking. You’re still responsible.

Motorway spray

Automatic headlights

Sensors rely on ambient light level rather than on vision and visibility as you see them, so they won’t always get it right.

  • Heavy rain or fog in daytime can reduce your vision and vehicle visibility to dangerous levels, but it might still be bright enough to prevent automated lights from coming on.
  • Around 1 in 10 drivers say they rely entirely on the car to decide when their headlights come on. That’s 1 in 10 vehicles invisible to others drivers in fog or heavy rain during the day.
Delayed reaction

Automatic lights might take a little time to react to changing light conditions too – if you drive into a tunnel it's best to switch your lights on manually.


There’s confusion over the correct use of sidelights.

  • The Highway Code says the only situation where you can drive with just your sidelights on is at night on a road which has lit street lighting.
  • Use headlights on other roads at night and in poor daytime visibility.

Daytime running lights (DRL)

New cars are now fitted with dedicated daytime running lights. Bright enough that they can be seen clearly in daylight, they’re too bright to be used at night so go off automatically when you turn your headlights on.

Daytime running lights are only fitted to the front so you won’t want to rely on them in the daytime when visibility is seriously reduced, as you could be virtually invisible from behind.

Waiting in a queue

You mustn’t use any lights in a way which would dazzle or cause discomfort to other road users.

More than a quarter of drivers admit to keeping their foot on the brake when stationary in a queue of traffic, but modern brake lights, particularly high-mounted central brake lights can be dazzling to look at for the driver behind you sat in a queue.

The Highway Code 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 says you should only flash your headlights to let others know you're there, but if other drivers are flashing you a lot it's worth checking your lights. Maybe there's a headlight or brake light not working.


The Highway Code and vehicle lighting

You must:
  • Use your sidelights between sunset and sunrise (rule 113).
  • Use your headlights at night except on a road with lit street lighting (113).
  • Use your 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 your front or rear fog lights unless visibility is seriously reduced (226).
  • Use your 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 your parking brake and take your foot off the footbrake in a stationary queue once following traffic has stopped (114).
  • Use your dipped headlights at night in built-up areas or in dull daytime weather, to ensure you can be seen (115).
  • Keep your headlights dipped when overtaking until you’re level with the other vehicle and only use main beam if this wouldn’t dazzle oncoming road users (115).
You may:
  • Use your front or rear fog lights in addition to your 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. Check your lights every couple of weeks by walking around the car, or take advantage of reflections in other vehicles, shop fronts or walls. Most journeys provide opportunities to check lights, front and rear.

Getting flashed?

The Highway Code (rule 110) says you should only flash your headlights to let other road users know that you're there, but if you find other drivers flashing you a lot then it would be worth checking your lights. Maybe there's a headlight or brake light not working.

31 January 2017