Свет резко погас, и в комнате стало темно.

In Russian, свет often works as a mass noun meaning light or the lighting in a place. So Свет погас is a very natural way to say that the light went out.

It does not necessarily mean just one lamp. It can describe the general lighting in the room.

You could also hear:

• Погас свет.
• Выключили свет. = the electricity / lights were turned off
• Света не стало. = there was no more light

So even if English uses a plural idea, Russian commonly uses singular свет.

Погас is the past masculine singular form of погаснуть, which means to go out, to be extinguished, or to stop shining/burning.

This verb is used for things like:

• lights
• candles
• fires
• flames
• stars

Examples:

• Свеча погасла. = The candle went out.
• Огонь погас. = The fire died out.
• Свет погас. = The light went out.

So Russian treats the light as something that suddenly stops shining.

The standard modern form is погас.

The infinitive is usually погаснуть, but in the past tense the common form is:

• погас (masculine)
• погасла (feminine)
• погасло (neuter)
• погасли (plural)

Some verbs in Russian have past forms that are a little irregular compared with what a learner might expect from the infinitive. So even though the infinitive has -ну-, the usual past form here is погас, not погаснул.

Here резко means something like abruptly, sharply, or suddenly. It emphasizes that the change happened quickly and noticeably.

So:

• Свет резко погас = The light went out abruptly.

A native English speaker might expect внезапно for suddenly, and that would also work:

• Свет внезапно погас.

The difference is small:

• внезапно focuses on surprise
• резко focuses on the abruptness of the change

There is a comma because this sentence joins two clauses, each with its own predicate:

1. Свет резко погас
2. в комнате стало темно

So this is basically:

• The light went out abruptly, and it became dark in the room.

In Russian, when и joins two independent clauses, a comma is normally used.

Стало темно is a very common impersonal Russian way to describe a change in the environment: it became dark.

Russian often uses this pattern:

• стало холодно = it became cold
• стало тихо = it became quiet
• стало грустно = it became sad
• стало темно = it became dark

If you say комната стала тёмной, that is grammatically possible, but it sounds more like you are describing the room as an object with a new quality: the room became dark. That is less natural here than the impersonal environmental description в комнате стало темно.

So the sentence is describing the situation in the room, not changing the room into a grammatical subject.

There is no real subject in the second clause. This is an impersonal construction.

In Russian, impersonal sentences often use:

• past tense neuter singular: было, стало, потемнело
• no explicit subject

So стало темно literally works like it became dark, where the English it is also not a real thing.

That is why Russian uses стало:

• not стал
• not стала
• not стали

The neuter singular is the normal form in many impersonal past constructions.

Here темно is a predicative word used in an impersonal construction. Learners often think of it as something like an adverb because it ends in -о, but in this sentence it functions as the main description of the situation:

• В комнате стало темно. = It became dark in the room.

Compare:

• тёмный = dark, dark-colored; an adjective
• темно = dark; used in expressions like here it is dark, it became dark

Other similar words:

• холодно
• жарко
• тихо
• страшно

These are very common in Russian.

В комнате means in the room and uses the prepositional case because it expresses location.

The noun is:

• комната = room
• prepositional singular: в комнате

So:

• в комнате = in the room
• в доме = in the house
• в школе = at school / in the school

If you are talking about motion into somewhere, Russian often uses the accusative instead:

• в комнату = into the room

But here there is no movement, only location, so в комнате is correct.

Yes, Russian word order is fairly flexible, and you could reorder parts of the sentence. But the original order sounds natural because it presents the cause-like event first and the resulting situation second:

• Свет резко погас, и в комнате стало темно.

This feels like:

1. the light went out
2. then the room was dark

If you reverse the clauses, the focus changes a little. Russian word order often helps show what is being presented first, what is being emphasized, and how the speaker wants the scene to unfold.

So the original version is natural and stylistically smooth.

Both are possible, but they are not exactly identical.

• В комнате стало темно = It became dark in the room.
• В комнате потемнело = It got dark in the room.

Потемнело is a single verb and is also very natural. But стало темно can sound slightly more descriptive and neutral.

The version in your sentence fits well because the first clause is about the light going out, and the second clause gives the resulting state:

• light went out
• it became dark

So стало темно works especially well as a result.

Погаснуть is a perfective verb. It describes a completed event: the light went out.

That fits this sentence well because the action is a single change:

• before: the light was on
• after: the light was off

Russian often uses perfective verbs for one completed event in the past.

If you wanted an imperfective idea, you would usually need a different structure or a different context, for example talking about a process, repetition, or background description.

So погас tells you the event happened as a whole, not as an ongoing action.

Not in natural English. The Russian structure is normal, but English needs a dummy subject:

• В комнате стало темно.
• natural English: It became dark in the room.

Russian does not need that kind of subject here. English does.

So when reading Russian, it helps to recognize that:

• стало темно
• было холодно
• будет тихо

often correspond to English it became dark, it was cold, it will be quiet.

They are related, but they are used differently.

• тёмный is an adjective
• темно is used in impersonal/predicative expressions

Examples:

• тёмная комната = a dark room
• В комнате темно. = It is dark in the room.

So in your sentence, темно is correct because the speaker is describing the condition in the room, not directly modifying the noun комната.