DGT Theory Topic 4, Vehicle Lights: a Visual Summary
Topic 4 of the Spanish DGT theory test: side lights, dipped and main beam, front and rear fog lights, clearance lights, hazard and brake lights, and dazzle — when each one is compulsory, with pictures, trick questions and a mini quiz.
Skilyapp Team
October 17, 2026
Topic 4 of the Spanish DGT syllabus covers vehicle lights: which ones a car has, what each one is for and when you must switch them on. It is a short topic, but the questions are very precise and nearly always hide a trick word: "by day", "travesía" (a road through a town), "light fog" or "dense fog". If you know what each light is for, the answer follows.
Here is the topic summarised with a picture of each light, the numbers you will be asked explained, the usual traps and a short quiz with real DGT questions. Spanish terms are shown in grey on the cards.
Legally, night runs from sunset to sunrise. At dusk, even if you can still see, your lights must be on.
In the test: the sun decides, not what you can see.
A road is poorly lit if you cannot read a number plate at 10 m or make out a dark car at 50 m.
In the test: the exam swaps the numbers: 10 to read, 50 to see.
You need all four conditions: night, outside a built-up area, a poorly lit road and more than 40 km/h.
In the test: never in a town, however dark the street.
Compulsory on vehicles over 2.10 m wide. Between 1.80 and 2.10 m, optional; below that, banned.
In the test: width is what counts, not height or load.
What topic 4 covers
| Part | What the exam asks |
|---|---|
| What lights are for | Seeing, being seen and signalling; when they are compulsory |
| Side, parking, reflector and clearance lights | What to leave on when parked at night, colours, the 2.10 m width |
| Dipped and main beam | When to use each, dipped beam by day, when main beam is banned |
| Fog lights | Front and rear, light or dense fog, the bends exception |
| Signalling lights | Indicators, hazard lights, brake lights and reversing lights |
| Dazzle and faults | Who dips first, what to do if dazzled, badly aimed headlights |
What lights are for and when to switch them on
Every light does one of three jobs: seeing (dipped beam, main beam and front fog lights), being seen (side lights, parking lights, reflectors, clearance lights and the rear fog light) or warning others (indicators, hazard lights, brake lights and reversing lights). There are also the interior light and the number plate light.
You must have at least side lights and dipped beam on in three situations:
- At night, on any road, from sunset to sunrise.
- In weather or conditions that reduce visibility: heavy rain, fog, snow, smoke or dust. By day too.
- In tunnels and underpasses and on stretches with the tunnel sign. By day too, even if they are lit.
If you are not sure there is enough light, switch on dipped beam, never main beam.
Side lights, parking lights, reflectors and clearance lights
Side lights (luces de posición) mark the vehicle: two white at the front and two red at the back. They come on whenever you use any other headlight. Driving with side lights alone is for a vehicle that is stopped or parked.
Parking lights (luces de estacionamiento) are half the side lights, the ones on the traffic side: one white at the front and one red at the back. What to leave on when parked at night:
| Where you park | Lights to leave on |
|---|---|
| Well-lit street | None |
| Street where the car cannot be seen from a distance | Side lights |
| Poorly lit travesía | Side lights or parking lights, or side lights on the traffic side if you are against the kerb |
| Shoulder of an interurban road | Side lights |
| Daytime with good visibility | None |
You never leave dipped or main beam on, nor hazard lights to excuse double parking.
Reflectors follow the same colour code: white at the front, red at the back, amber on the sides. Triangular ones are only for trailers and semi-trailers. Clearance lights (luces de gálibo) show the width and height of large vehicles: compulsory above 2.10 m wide, and in a tunnel they are always on, by day too.
Dipped beam and main beam
Dipped beam (luz de cruce) is the main light: it lights up the road ahead without dazzling oncoming traffic. It only exists at the front; at the back a car has side, brake and fog lights, but no dipped beam. Main beam (luz de carretera) is the exception: only when all four conditions are met (night, outside a built-up area, poorly lit road and over 40 km/h). If one is missing, dipped beam.
Dipped beam is compulsory by day too:
- In tunnels and underpasses, even lit ones.
- In special lanes: reversible, temporary extra lanes and contraflow lanes.
- On motorcycles, on every road, always.
The HOV lane (carril VAO) is not on that list: no lights needed there by day. This is the most common trap in this section.
Main beam is banned: in built-up areas (including travesías, however dark), whenever you could dazzle someone (oncoming traffic, the driver ahead through their mirror, pedestrians or cyclists) and on a stopped or parked vehicle. One curious exception: in a dark tunnel on an interurban road, above 40 km/h with nobody ahead or oncoming, main beam is the right choice.
Headlight flashes (switching from dipped to main beam for a moment) are for warning of an overtake outside towns or of a hazard. Never to dazzle, hurry or annoy someone.
All of topic 4, one short lesson at a time
16 short lessons in Skilyapp: an everyday situation, 2 to 4 slides with a picture of each light, and 1 or 2 DGT questions with the answer explained.
Fog lights: front and rear
The front fog light is white, low and wide: it lights the road surface beneath the fog. It is optional. The rear fog light is red and very bright, brighter than the brake lights, and it is compulsory on motor vehicles except motorcycles, tricycles, trailers and semi-trailers. Motorcycles may fit both if they want.
What decides which one you use is how much visibility drops:
| Conditions | Compulsory | Optional extra |
|---|---|---|
| Fog, heavy rain, snowfall, smoke or dust | Side lights + dipped beam | Front fog lights or main beam |
| Dense fog, very heavy rain, heavy snowfall, thick smoke or dust | Side lights + dipped beam + rear fog light | Front fog lights or main beam |
One word changes the answer: in "heavy" rain the rear fog light is not compulsory; in "very heavy" rain it is. In light fog, the front ones. When visibility improves, switch the rear one off: it dazzles the driver behind and hides your brake lights.
The only time the front fog lights go on without bad weather: at night, on a stretch with the dangerous bends sign, where the carriageway is 6.50 m wide or less. Not on a straight road without fog, not on a travesía with good visibility, not in a tunnel.
Indicators, hazard lights, brake and reversing lights
Indicators are amber and warn of a sideways move: turning, changing lanes, pulling out of a parking space or overtaking. They work the same by day and by night, and they warn others; they do not give you priority.
Hazard lights (all four indicators at once) say your vehicle is a danger. They are compulsory on cars, lorries and buses; motorcycles may have them. Use them when the vehicle is stopped by a breakdown or accident (together with the V-16), when moving in an emergency, and when you cannot reach the road's minimum speed. They do not make double parking legal.
Brake lights are red: two at the sides and a third, higher, in the middle. Several flashes in a row warn those behind that you are about to brake or stop, because the eye gets used to a steady light but notices a flash at once. The reversing light is the only white light facing backwards (apart from the number plate light): if it is on, that car is coming towards you.
The interior light stays off when driving at night: the windows reflect the cabin and you see the road worse (in buses, taxis and VTC it is compulsory, without dazzling anyone). The rear number plate is lit together with the side lights. Unauthorised lights and colours are banned: neon strips, tinted headlights or more lights than allowed.
Dazzle and badly aimed headlights
Whenever you could dazzle someone, switch from main beam to dipped: oncoming traffic, the vehicle ahead going your way (through its mirrors), pedestrians and cyclists.
- When overtaking: whoever is behind uses dipped beam. You catch up a slow car and dip; once you are alongside you may go back to main beam, and from then on it is the overtaken driver who dips.
- On a tight bend: the driver for whom the bend goes to the right dips first, because their headlights point straight into the opposite lane.
- If you are dazzled: slow down as much as needed, even to a stop, and look at the right-hand edge of the road, not at the headlights. Speeding up or switching on your own main beam is the trap answer.
A heavy load at the back lifts the nose and the dipped beam points too high: it dazzles. Adjust the headlight height. And drive at a speed that lets you stop within the area your lights illuminate. If your main beam fails at night on an open road, slow down and carry on with dipped beam.
Trick answers in topic 4
| What sounds logical | What the exam wants |
|---|---|
| If you can still see at dusk, no lights needed | Lights on from sunset |
| On a dark village street you may use main beam | Never in towns or on travesías |
| 50 m to read the plate, 10 m to see the car | The other way round: 10 to read, 50 to see |
| Dipped beam by day in the HOV lane | No: only tunnels, reversible, extra and contraflow lanes, and motorcycles |
| Main beam is always banned in tunnels | In a dark interurban tunnel with nobody around, it is the right one |
| Heavy rain: rear fog light | Only in very heavy rain or dense fog |
| Light fog: rear fog light | Front fog lights |
| Clearance lights from 1.80 m | Compulsory from 2.10 m wide |
| If dazzled, switch on main beam to see better | Slow down, even to a stop |
| On a bend the driver turning left dips first | The one turning to their right |
Mini quiz: 8 real exam questions
These are official DGT questions on topic 4, translated from the Spanish. Pick an answer to see whether you got it and why.
Question 1 / 8
Two vehicles meet on a tight bend...
Whoever turns to their right has headlights pointing into the opposite lane and dazzles first, so they dip first.
Question 2 / 8
May a motorcycle be fitted with hazard lights?
On motorcycles hazard lights are optional: they may have them, whatever the engine size, and if fitted they use them.
Question 3 / 8
When must a vehicle wider than 2.10 metres drive through a tunnel with its clearance lights on?
Lights are compulsory in tunnels at any time, and for vehicles over 2.10 m that includes clearance lights.
Question 4 / 8
Which fog light should you switch on in light fog?
The rear one is for dense fog. In light fog, the front ones (if the car has them).
Question 5 / 8
Driving at night on a poorly lit urban road, which lights must be on?
Main beam is never used in towns, even on a dark street: side lights and dipped beam.
Question 6 / 8
What should a driver do when dazzled by the lights of an oncoming vehicle?
While you cannot see, every second is metres driven blind. Brake as much as needed, even to a standstill.
Question 7 / 8
You are on main beam and catching up a slower vehicle going the same way. Should you switch to dipped beam?
Your main beam shines into the mirrors of the car ahead. While you are behind it, dip.
Question 8 / 8
Driving at night at the speed limit on a poorly lit road outside town, your main beam fails. What should you do?
With dipped beam you see less far, so slow down enough to stop within the lit area.
How to learn topic 4
Always ask what a light is for: seeing, being seen or warning? Then watch for the words that change the answer: "by day" (tunnels, special lanes, motorcycles), "travesía" (it is a town: never main beam), "light" or "dense" (front or rear fog light). And the numbers: 10 and 50 m, over 40 km/h, 2.10 m and 6.50 m.
Driving in fog and rain is also covered in the topic 7 summary, and the V-16 and breakdowns in the topic 2 summary.
Study topic 4 with pictures and DGT questions
Each lesson takes a few minutes and ends with real exam questions, answers explained. Learn at your own pace on your phone.
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¿Cuándo se puede usar la luz de carretera? +
De noche, fuera de poblado, en vías insuficientemente iluminadas y a más de 40 km/h, siempre que no deslumbres a nadie. En poblado y en travesías está prohibida.
¿Cuándo es obligatoria la antiniebla trasera? +
Con niebla espesa, lluvia muy intensa, nevada densa o humo o polvo denso. Con niebla ligera o lluvia intensa no es obligatoria.
¿Hay que llevar la luz de cruce de día? +
Sí en túneles y pasos inferiores, en los carriles reversible, adicional y en sentido contrario, y siempre en motocicleta. En el carril VAO no.
¿Quién cambia primero a la luz de cruce en una curva cerrada? +
El que toma la curva a su derecha, porque sus faros apuntan directamente al carril contrario.
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