Learn Hardcore Norwegian: Han slår av lyset i stuen når han går og legger seg. - He turns off the light in the living room when he goes to bed.

slår on its own is the verb å slå, whose basic meaning is to hit / to strike.
When combined with av (off), slår av becomes an idiomatic expression: to turn off.

You can think of it like English “switch off”, where switch literally means a mechanical switch, but in use it just means turn off.

You will also often hear:

skru av lyset – literally screw off the light, but idiomatically also turn off the light.
Both slå av lyset and skru av lyset are common and natural.

Why is it lyset and not just lys? What does the -et ending mean?

Lys means light (in general).
Lyset means the light (a specific light).

Norwegian marks the definite article as a suffix instead of using a separate word like English the:

et lys – a light (indefinite, neuter noun)
lyset – the light (definite, neuter singular)

So slår av lyset literally means “turns off the light”, referring to a specific light (for example, the main light in the living room).

Why is it i stuen and not på stuen? What’s the difference between i and på here?

Both i and på can mean in in English, but they’re used differently.

i is used for being inside an enclosed space or room.
på is more like on, but is also used for some set expressions and certain types of places.

For rooms in a house, the default is i:

i stuen – in the living room
i kjøkkenet (less common; often just på kjøkkenet is used colloquially)
i badet (again, på badet is also common)

For stue specifically, i stuen is the normal, standard choice when you mean inside the living room.
So lyset i stuen = the light in the living room.

Why is it stuen and not stua? Are both correct?

Both stuen and stua are correct; they’re just different forms of the same word.

The basic noun is (en) stue – a living room.
Definite singular can be:
- stuen – more bookish / standard Bokmål
- stua – more colloquial / spoken Bokmål

So:

i stuen – in the living room (more formal/standard)
i stua – in the living room (very common in everyday speech)

In a textbook, you’re more likely to see stuen. In conversation, you’ll often hear stua.

Why does it say går og legger seg instead of just legger seg? What does går og add?

The phrase går og + verb is a common Norwegian pattern. Literally it means “goes and [does something]”, but often it just softens the action a bit or emphasizes the movement towards doing it.

han legger seg – he lies down / he goes to bed
han går og legger seg – he goes and lies down / he goes to bed

Here, går og adds a sense of going off to do something (moving from where he is now, then going to bed). It can sound a bit more natural and vivid than simply legger seg, especially when talking about the routine of going to bed.

Other examples:

Jeg går og dusjer. – I’ll go (and) take a shower.
Hun går og lager mat. – She’s going to make food / she goes and makes food.

Why is it legger seg and not just legger? What does seg do?

Legger seg comes from the verb å legge seg, which is a reflexive verb meaning to lie down / to go to bed.

å legge = to lay (something down)
å legge seg = to lay oneself down → to lie down / go to bed

In Norwegian, many actions you do to yourself use seg (or meg, deg, oss, dere depending on the subject):

jeg legger meg – I go to bed / I lie down
han legger seg – he goes to bed
de legger seg – they go to bed

Without seg, legger needs a direct object:

Han legger boka på bordet. – He puts the book on the table.

With seg, the person is both the doer and the receiver of the action, which fits the meaning to go to bed / lie down.

Why is the present tense (slår, går, legger) used here if this is a habit?

Norwegian uses the simple present tense for:

actions happening right now
habits and repeated actions
general truths

So Han slår av lyset i stuen når han går og legger seg naturally expresses a habitual action:
He turns off the light in the living room when he goes to bed.

This works just like English:

He turns off the light when he goes to bed. (habit)
He turns off the light right now. (present action)

Norwegian doesn’t need a special tense form for habits; the regular present tense does the job.

What’s the difference between når and da, and why is når used here?

Both når and da can translate to when in English, but their use is different:

når is used for:
- repeated / habitual actions in the past, present, or future
- general time clauses
da is generally used for:
- one specific event in the past

In this sentence, the action is repeated – every time he goes to bed, he turns off the light. So når is correct:

Han slår av lyset i stuen når han går og legger seg.
– He turns off the light when he goes to bed. (every time)

For a single past event, you’d use da:

Han slo av lyset i stuen da han gikk og la seg.
– He turned off the light when he went to bed. (one particular time)

Is the word order Han slår av lyset i stuen når han går og legger seg fixed, or can I move the når-clause?

You can move the når-clause to the front, but then you must respect Norwegian V2 word order (the verb is the second element in a main clause).

Both of these are correct:

Han slår av lyset i stuen når han går og legger seg.
Når han går og legger seg, slår han av lyset i stuen.

In (2), the når-clause comes first, and then the main clause follows with:

slår (verb) as the second element in that clause
han (subject) after the verb

What you can’t say is:

✗ Når han går og legger seg, han slår av lyset i stuen. (incorrect)

That would violate the V2 rule in the main clause.

Could you leave out i stuen and just say Han slår av lyset når han går og legger seg?

Yes, you can. That sentence is also completely correct:

Han slår av lyset når han går og legger seg.
– He turns off the light when he goes to bed.

Without i stuen, it’s less specific; it just means the light – probably the main light wherever he is. Adding i stuen specifies which light: the light in the living room.

So:

With i stuen: focuses on where the light is.
Without i stuen: focuses simply on the action of turning off the light.