Gece sessiz olunca daha rahat uyuyabiliyorum.

to be

Breakdown of Gece sessiz olunca daha rahat uyuyabiliyorum.

• daha: more
• gece: the night
• sessiz: quiet

Questions & Answers about Gece sessiz olunca daha rahat uyuyabiliyorum.

Why does the sentence start with gece? Does it mean night or at night?

Here gece means at night / when it is night.

In Turkish, many time words can be used without a case ending to mean during that time:

• sabah = in the morning
• akşam = in the evening
• gece = at night

So gece here is not just a dictionary-style night. In this sentence, it functions like a time expression: at night.

You could think of the beginning as:

• Gece ... = At night, ...

Why is it sessiz olunca and not just sessizken?

Both are possible in Turkish, but they are not exactly the same in feel.

• sessizken = when it is quiet / while it is quiet
• sessiz olunca = literally when it becomes quiet, but very often it is also used in the broader sense of when it is quiet

In everyday Turkish, olunca is extremely common for expressing a condition or situation that happens and then leads to a result.

So:

• Gece sessizken daha rahat uyuyabiliyorum.
• Gece sessiz olunca daha rahat uyuyabiliyorum.

Both are natural.
The version with olunca can sound a bit more like when the night is quiet / once things are quiet at night.