bang jeonguga gapjagi nagaseo bame chaegeul mos ilgeosseoyo.

In Korean, two nouns are often placed directly next to each other without 의 when the relationship is obvious.

• 방 전구 = the room bulb / the bulb in the room
• 방의 전구 is also possible, but it sounds more explicit or a little less conversational

So 방 전구가 is a natural compressed way to say the bulb in the room.

They mark different grammatical roles in the two parts of the sentence.

• 전구가: 가 marks the subject of the first clause
  → the bulb is the thing that went out
• 책을: 을 marks the object of the second clause
  → the book is the thing that the speaker couldn’t read

Even though it is one sentence, it contains two linked clauses, so each clause can have its own marker.

Here, 나가다 is being used in a very common idiomatic way.

With things like lights, electricity, or appliances, 나가다 can mean:

• to go out
• to stop working
• to burn out

So 전구가 나가다 means the light bulb went out or burned out.
It does not mean the bulb physically left the room.

Here -아서/-어서 links two clauses and gives a cause/result meaning.

So:

• 전구가 나가서
• literally: the bulb went out, so...
• naturally: because the bulb went out...

In this sentence, it explains the reason for the second part:

• the bulb went out
• so the speaker couldn’t read

Also, because 나가다 has ㅏ in the stem, it becomes 나가서 rather than 나가어서.

This is an important difference.

• 못 읽었어요 = couldn’t read
• 안 읽었어요 = didn’t read

못 expresses inability or that circumstances prevented the action.
Since the light bulb went out, the speaker was unable to read.

So 못 is the correct choice here.

밤에 means at night.

The particle 에 is often used with time expressions to show when something happened.

• 밤에 = at night
• 아침에 = in the morning
• 저녁에 = in the evening

So 밤에 책을 못 읽었어요 means the not-reading happened at night.

Depending on context, it can mean either:

• at night in general
• or that night in a specific story

This word is tricky for many learners.

읽었어요 is usually pronounced roughly as 일거써요.

That is because the verb stem 읽- changes in pronunciation when followed by a vowel-starting ending. So the written form and spoken form do not match letter-for-letter in the way an English speaker might expect.

A good practical pronunciation to aim for is:

• 일거써요

Because the sentence is describing a completed past event.

The speaker is talking about what happened:

• the bulb went out
• as a result, they couldn’t read

So 읽었어요 is the polite past form.

Compare:

• 못 읽었어요 = couldn’t read
• 못 읽어요 = can’t read / don’t read

Here, the past tense fits the situation.

Yes. Korean adverbs are fairly flexible.

In this sentence, 갑자기 comes before the verb it modifies:

• 방 전구가 갑자기 나가서

That is very natural.

You could also say:

• 갑자기 방 전구가 나가서...

The basic meaning stays the same, but the emphasis shifts slightly. Putting 갑자기 near the verb is very common.

It is understandable and works, but Korean speakers might also say similar things in slightly different ways depending on what they want to focus on.

For example:

• 방 전구가 나가다 → the bulb in the room went out
• 방 불이 나가다 → the light in the room went out
• 방 전등이 나가다 → the lamp/light fixture went out

So 전구 specifically focuses on the bulb itself.
Other versions may sound more natural in some everyday situations, but the original sentence is still fine.

Yes, very much so.

Because of -아서/-어서, the sentence has a natural reason/explanation feel:

• the bulb went out,
• so I couldn’t read

This pattern is commonly used when explaining why something happened. It can sound like a neutral explanation, not necessarily an excuse, depending on context and tone.