Het licht gaat vanzelf uit als het buiten licht wordt.

Because uitgaan is a separable verb in Dutch.

• Full verb: uitgaan = to go out, to switch off
• In a main clause, the verb splits:
  • Het licht gaat uit.
• The conjugated part (gaat) stays in the normal verb position, and the prefix (uit) moves to the end.

So:

• Het licht gaat uit = the light goes out / turns off

This is very common in Dutch:

• Ik doe het raam open. = I open the window.
• De tv gaat aan. = The TV turns on.

Vanzelf means by itself, automatically, or on its own.

So:

• Het licht gaat vanzelf uit = the light switches off automatically

It often suggests that no person needs to do anything.

You can also hear it in other contexts:

• De deur gaat vanzelf dicht. = The door closes by itself.
• Dat spreekt vanzelf. = That goes without saying / that is obvious.

The two het words do different jobs.

1. Het licht
   Here het is the definite article for the noun licht:

   • het licht = the light

2. als het buiten licht wordt
   Here het is a dummy subject or formal subject, similar to English it in:

   • it gets dark
   • it is raining

Dutch often uses het with weather, time, and general environmental conditions:

• Het regent. = It is raining.
• Het wordt donker. = It is getting dark.
• Het wordt buiten licht. = It is getting light outside.

So the second het does not refer to the lamp. It is just the normal subject used in this kind of sentence.

No, it is not the same part of speech both times.

1. het licht
   Here licht is a noun:

   • the light

2. het buiten licht wordt
   Here licht is an adjective:

   • light
   • meaning bright or daylight-like

So the sentence uses the same word form in two different ways:

• het licht = the lamp/light
• licht worden = become light / get light outside

This is normal in Dutch, just as English can use light as both a noun and an adjective.

Because als het buiten licht wordt is a subordinate clause introduced by als.

In Dutch subordinate clauses, the finite verb usually goes to the end.

Compare:

• Main clause: Het wordt buiten licht.
• Subordinate clause: als het buiten licht wordt

This is one of the most important Dutch word-order rules.

More examples:

• Ik ga naar huis als het laat wordt.
• We blijven binnen omdat het regent.

In both cases, the conjugated verb is at the end of the subordinate clause.

Because worden means to become, and the idea is a change of state.

• Het is licht. = It is light.
• Het wordt licht. = It is becoming light / It is getting light.

So licht worden means to become light, not simply to be light.

That matches the idea of dawn or daylight arriving.

English often uses get in this kind of sentence:

• It gets dark
• It gets cold
• It gets light

Dutch often uses worden for the same idea:

• Het wordt donker.
• Het wordt koud.
• Het wordt licht.

Buiten means outside.

In this sentence, it tells you where it is becoming light:

• het buiten licht wordt = it gets light outside

Without buiten, het licht wordt would still mean it gets light, but adding buiten makes it clear that we are talking about the outdoor environment, not the lamp itself.

So the sentence contrasts:

• the indoor light turning off
• because outside it is becoming daylight

Als can often mean if or when, depending on context.

Here it means when:

• Het licht gaat vanzelf uit als het buiten licht wordt.
• The light turns off automatically when it gets light outside.

Why when here? Because this is describing a regular, expected event, not an uncertain possibility.

Very roughly:

• als = if / when
• in repeated or general situations, English often translates it as when

Examples:

• Als ik tijd heb, lees ik. = When I have time, I read.
• Als het regent, blijven we binnen. = If/when it rains, we stay inside.

So here when is the most natural English translation.

Yes. They are related, but not the same.

• Het licht gaat uit. = The light goes out / turns off.
  This describes the action or change.

• Het licht is uit. = The light is off.
  This describes the state after the change.

So in your sentence:

• gaat ... uit is correct because the sentence talks about the moment or process of switching off automatically.

Compare:

• Om 7 uur gaat het licht uit. = At 7 o’clock the light turns off.
• Na 7 uur is het licht uit. = After 7 o’clock the light is off.

Because buiten belongs naturally before the adjective licht here.

The pattern is:

• het wordt licht = it gets light
• het wordt buiten licht = it gets light outside

So buiten works as an adverb modifying the whole situation, and licht stays as the complement with worden.

The order het licht buiten wordt sounds unnatural in standard Dutch.

A useful way to think of it is:

• worden + adjective
• and adverbs like buiten come before that adjective

Examples:

• Het wordt hier koud. = It is getting cold here.
• Het wordt morgen warm. = It will get warm tomorrow.
• Het wordt buiten licht. = It is getting light outside.

Yes, absolutely.

Both are possible, but they focus slightly differently:

• Het licht gaat vanzelf uit. = The light turns off automatically.
• De lamp gaat vanzelf uit. = The lamp turns off automatically.

Het licht focuses more on the light itself, as a function or source of illumination.
De lamp focuses on the physical object.

In everyday speech, both are common depending on what exactly the speaker wants to emphasize.

No.

• licht worden = become light / get light
• lichter worden = become lighter

Lichter is the comparative form, like lighter in English.

So:

• Het wordt licht. = It’s getting light.
  This refers to daylight or brightness in a general sense.

• De kamer wordt lichter. = The room is getting lighter.
  This compares the room to how it was before.

In your sentence, licht is the normal and correct word, because the idea is daylight coming, not more light than before in a comparative sense.