Assim que a lâmpada nova estiver no lugar, vou fechar a cortina e começar o filme.

Assim que means as soon as or once.

It introduces an action that will happen immediately after another one:

• Assim que a lâmpada nova estiver no lugar...
• As soon as the new light bulb is in place...

It is very common in Portuguese for talking about future events that depend on something else happening first.

Because after assim que, Portuguese normally uses the future subjunctive when the action is still in the future.

So:

• assim que ... estiver = correct
• assim que ... está = not natural here
• assim que ... estará = grammatically possible in other contexts, but not the normal pattern after assim que

A good rule is: after words like quando, assim que, logo que, and se, Portuguese often uses the future subjunctive for future situations.

Estiver is the future subjunctive form of the verb estar.

In this sentence, it means something like is / will be, but specifically in a future, uncertain, or not-yet-completed situation:

• quando eu estiver
• se ele estiver
• assim que a lâmpada estiver

This is a very common irregular form, so it is worth memorizing.

Both can express the future, but vou + infinitive is much more common in everyday Brazilian Portuguese.

So:

• vou fechar a cortina = I’m going to close the curtain
• fecharei a cortina = I will close the curtain

The simple future (fecharei) is correct, but it can sound more formal, literary, or emphatic in many situations.

Because one auxiliary verb can apply to two infinitives when they share the same subject and time reference.

So:

• vou fechar a cortina e começar o filme

means:

• vou fechar a cortina e vou começar o filme

The second vou is simply omitted because it is understood.

Portuguese often leaves out subject pronouns when the verb already makes the subject clear.

Here, vou clearly means I am going to, so eu is unnecessary:

• vou fechar a cortina
• eu vou fechar a cortina

Both are correct. Adding eu can give extra emphasis, contrast, or clarity, but it is not required.

Portuguese uses definite articles very often, especially when referring to specific things already known in the situation.

Here:

• a lâmpada nova = the new light bulb
• a cortina = the curtain

In context, these are probably specific objects in the room, so the definite article sounds natural. Portuguese generally uses articles more often than English does.

Adjectives often come after the noun in Portuguese, so:

• lâmpada nova = new light bulb

Also, lâmpada is a feminine singular noun, so the adjective must agree with it:

• novo = masculine singular
• nova = feminine singular

That is why it is a lâmpada nova, not o lâmpada novo.

No lugar means in place, in its place, or where it belongs.

No is a contraction:

• em + o = no

So literally, no lugar is in the place.

In this sentence, it means the new light bulb has been properly installed or put where it should be.

Yes, you could say Quando a lâmpada nova estiver no lugar..., and it would be correct.

The difference is mainly nuance:

• assim que = as soon as, with a stronger sense of immediacy
• quando = when, more neutral

So assim que suggests: the moment the bulb is in place, I’ll do the next things.

Usually começar o filme means start the movie in the sense of put it on / begin playing it.

If you want to emphasize watching, Portuguese might use:

• começar a assistir ao filme

But in everyday speech, começar o filme is very natural when the meaning is clear from context.

Yes, it is standard to use a comma here because the sentence begins with a subordinate time clause:

• Assim que a lâmpada nova estiver no lugar, vou fechar a cortina e começar o filme.

The comma separates the introductory clause from the main clause. In Portuguese, this is the normal punctuation pattern.

Because estar is used for states, positions, and temporary conditions.

Here, estar no lugar means to be in place / to be where it should be. That is a location or resulting state, so estar is the natural choice.

Ser would not work here because it is not describing identity or an inherent characteristic.