اتاق من روشن نیست، چون پرده ها بسته هستند.

In Persian, possession is usually shown with the order:

noun + possessor

So:

• اتاق من = my room
• literally: room of me

This is different from English, where my comes before the noun.

You may also hear the shorter form:

• اتاقم = my room

Both are correct. اتاق من is a little fuller and often clearer for learners.

Persian often leaves out the present-tense form of to be in the third person singular when the sentence is positive.

So:

• اتاق من روشن است = My room is bright/lit
• اتاق من روشنه = spoken Persian
• but very often you may also hear just اتاق من روشن in certain contexts

In negative sentences, however, Persian normally uses نیست:

• روشن نیست = is not bright/lit

So نیست is the negative form of است here.

روشن can mean:

• bright
• light
• lit
• illuminated
• sometimes even clear depending on context

In اتاق من روشن نیست, it means something like:

• My room is not bright
• My room is not lit

Because the second clause talks about the curtains being closed, the idea is that the room is dark due to lack of light.

چون means because.

It introduces a reason:

• اتاق من روشن نیست، چون پرده ها بسته هستند.
• My room is not bright, because the curtains are closed.

It works much like English because.

Other Persian words for because include:

• زیرا — more formal
• به خاطر اینکه — more conversational / explanatory

But چون is very common and natural.

Yes. ها is the common plural marker in Persian.

So:

• پرده = curtain
• پرده‌ها = curtains

It may appear as:

• پرده ها
• پرده‌ها

The version with the little connector/joiner, پرده‌ها, is usually preferred in careful writing, but both are commonly seen.

Persian usually does not have a separate word exactly like English the.

So پرده‌ها can mean:

• curtains
• the curtains

The context tells you which one is meant.

In this sentence, since we are talking about the curtains in the room, English naturally translates it as the curtains.

Because پرده‌ها is plural.

• پرده‌ها = the curtains / curtains
• plural subject → plural form of to be

So:

• پرده بسته است = The curtain is closed
• پرده‌ها بسته هستند = The curtains are closed

Here:

• است = is
• هستند = are

بسته literally means closed.

It is the past participle of the verb بستن (to close, to shut, also to tie in other contexts).

In this sentence, it functions like an adjective:

• بسته هستند = are closed

This is very common in Persian:

• در باز است = The door is open
• پنجره بسته است = The window is closed

So بسته describes the state of the curtains.

In everyday Persian, the copula is often dropped in the present tense, especially in informal speech.

So you may hear:

• پرده‌ها بسته هستند — fully explicit, clear
• پرده‌ها بسته‌اند — same meaning, more compact
• پرده‌ها بسته‌ان — colloquial pronunciation
• sometimes even پرده‌ها بسته‌ست would be wrong here, because the subject is plural

For learners, بسته هستند is a very clear and correct form.

In Persian, predicate adjectives usually come after the subject.

So:

• اتاق من روشن نیست
  literally: my room bright is not
• پرده‌ها بسته هستند
  literally: the curtains closed are

This is normal Persian sentence structure.

Notice that this is different from an adjective directly modifying a noun. For example:

• اتاق روشن = a bright room
• پرده بسته = a closed curtain

But in your sentence, the adjectives are part of the predicate, so they come after the subject and before the form of to be.

A common spoken version would be:

• اتاق من روشن نیست، چون پرده‌ها بسته‌ان.

Or even:

• اتاقم روشن نیست، چون پرده‌ها بسته‌ان.

Changes you might hear in speech:

• اتاق من → اتاقم
• هستند → ـان / ان
• pronunciation is smoother and less formal

But the written sentence you were given is completely correct and good for learning.

They mean the same thing:

• اتاق من = my room
• اتاقم = my room

The difference is mainly style:

• اتاقم is shorter and very common in natural Persian
• اتاق من can sound a bit more explicit, emphasized, or careful

Learners often see اتاق من first because it is easier to recognize.

Yes. روشن can refer to light in a general sense, so روشن نیست may suggest:

• the room is dark
• the room is not illuminated
• the light is not on, depending on context

But because the reason given is the curtains are closed, the sentence specifically suggests lack of daylight rather than an electric light being switched off.

The comma helps separate the main statement from the reason:

• اتاق من روشن نیست، چون...

In Persian punctuation, this is common and similar to English. It is helpful but not always absolutely required in casual writing. In careful writing, it makes the sentence easier to read.