Vehicle Lighting Rules: When Trucks Must Light Up and When Fog Lights Become an Offence

Lighting rules sit in an odd corner of compliance: every driver thinks they know them, roadside checks keep proving otherwise, and the offences are cheap to commit and easy to prove. Highway Code rules 113 to 116 carry the core requirements - several of them MUSTs backed by the Road Vehicles Lighting Regulations - and they deserve a place in every fleet’s driver briefing.

What must be lit, and when

Rule 113 sets the baseline duties:

• All sidelights and rear registration plate lights must be lit between sunset and sunrise. The number plate lamp is the one fleets forget: a dead plate bulb is an offence in its own right and one of the easiest roadside finds there is.
• Headlights must be used at night, except on roads with lit street lighting - generally 30mph restricted roads, or 20mph in Wales. Outside lit areas, headlights at night are not optional.
• Headlights when visibility is seriously reduced - the rule 226 duty, generally when you cannot see beyond 100 metres - applies day or night.

The rule even defines its terms: “night”, the hours of darkness, means the period from half an hour after sunset to half an hour before sunrise. Dusk is not a grey area; it is a defined window, and “I hadn’t put them on yet” has a clock attached.

Dazzle: the other direction

Rule 114 polices over-lighting as firmly as under-lighting:

• You must not use any lights in a way that would dazzle or cause discomfort to other road users - pedestrians, cyclists and horse riders included.
• Front or rear fog lights must not be used unless visibility is seriously reduced, and must be switched off when visibility improves. A rear fog lamp left on in clear conditions dazzles following drivers and can mask brake lights.

The same rule adds a queueing courtesy that is worth teaching: in stationary traffic, apply the parking brake and, once the traffic behind has stopped, come off the footbrake so your brake lights go out. A truck’s high-mounted brake lights at eye level of the car behind are a real glare source in night queues.

Being seen and seeing: rule 115

The advisory layer:

• Use dipped headlights (or dim-dip where fitted) at night in built-up areas and in dull daytime weather, so the vehicle can be seen.
• Keep headlights dipped when overtaking until level with the other vehicle, then main beam if needed - unless it would dazzle oncoming traffic.
• If dazzled by oncoming headlights, slow down and if necessary stop.

For HGVs the overtaking point has extra weight: a truck’s main beam sits at car windscreen height, and the “level with the other vehicle” timing is the difference between a legal overtake and a dazzled driver.

Hazard warning lights: rule 116

Hazard lights have exactly two legitimate uses in the rule:

• Stationary: to warn that your vehicle is temporarily obstructing traffic - and never as an excuse for dangerous or illegal parking. Hazard lights do not legalise a bad stop; they just advertise it.
• Moving: you must not use them while driving or being towed, except on a motorway or unrestricted dual carriageway to warn drivers behind of a hazard or obstruction ahead - and only for long enough for the warning to be seen.

The moving exception is a genuinely useful tool for trucks: a loaded HGV that spots a queue around a bend can warn a mile of following traffic with one button press. But it is a warning, not a mode: hazards on for the next ten miles “because it’s raining” is both outside the rule and useless as a signal.

None of this is exotic. What makes lighting rules worth a briefing of their own is how visible the failures are: a truck running without a plate lamp or with a fog light blazing is announcing a maintenance culture problem to every traffic car behind it, and inviting the stop that finds the rest.

The fleet angle

Lighting is where the walkaround check and the Highway Code meet. The daily check already covers lamps, reflectors and markers; rules 113 to 116 are what drivers do with them. A fleet briefing worth running once a year:

• Night starts 30 minutes after sunset, plate lights included.
• Fog lights are for seriously reduced visibility only - and they go off when it lifts.
• Dip before you draw level; a truck’s beam is another driver’s eyesight.
• Hazards warn; they do not excuse.

Lighting offences are strict, visible and cheap to avoid. There is no good reason for a professional fleet to collect them.

Sources

• The Highway Code: General rules, techniques and advice for all drivers and riders (103 to 158) (GOV.UK)