Espera, a menos que as luzes parem de piscar.

Espera is the informal singular imperative of esperar — the form you use when telling one person that you know well to wait.

• espera = wait! (to one person, informal — *tu)*
• espere = wait! (formal singular — *você/o senhor/a senhora)*
• esperem = wait! (plural, formal or standard plural command)

So Espera here sounds like Wait! said directly to one person in an informal way.

In Portuguese, subject pronouns are often left out when the verb already makes the subject clear.

So instead of saying:

• Tu espera

Portuguese normally just says:

• Espera

The verb form already shows that this is a command directed at you. This is very natural in Portuguese.

A menos que means unless.

It introduces an exception to what was just said:

• Espera = wait
• a menos que... = unless...

So the full sentence means something like:

• Wait, unless the lights stop flashing.

This expression is commonly followed by the subjunctive, which is why you get parem and not param.

Because a menos que normally requires the subjunctive mood in Portuguese.

Here:

• parar = to stop
• parem = present subjunctive, 3rd person plural

Since as luzes is plural, the verb also has to be plural:

• a luz pare = the light stops
• as luzes parem = the lights stop

So a menos que as luzes parem is grammatically expected after a menos que.

These two forms look similar but belong to different moods:

• param = indicative
• parem = subjunctive

After a menos que, Portuguese uses the subjunctive, so parem is the correct choice.

Compare:

• As luzes param de piscar. = The lights stop flashing. (statement, indicative)
• ...a menos que as luzes parem de piscar. = ...unless the lights stop flashing. (after *a menos que, subjunctive)*

Portuguese often uses definite articles more often than English does.

• as luzes = the lights

In English, depending on context, you might sometimes say just lights, but Portuguese usually prefers the article when talking about a specific set of lights already understood from the situation.

So as luzes sounds natural and specific here.

This is the common structure:

• parar de + infinitive = to stop doing something

So:

• piscar = to blink / to flash
• parar de piscar = to stop blinking / to stop flashing

Examples:

• Para de falar. = Stop talking.
• A máquina parou de funcionar. = The machine stopped working.
• As luzes pararam de piscar. = The lights stopped flashing.

So parem de piscar means stop flashing.

It can mean both, depending on the subject.

With eyes:

• piscar os olhos = to blink

With lights:

• as luzes piscam = the lights blink / flash

In this sentence, since the subject is as luzes, the most natural English translation is usually flash or blink.

Because the subject is plural:

• a luz = the light
• as luzes = the lights

So the verb must agree with the subject:

• a luz pare
• as luzes parem

This is standard subject-verb agreement.

Yes, deixar de + infinitive can also mean to stop doing something.

So you could say:

• a menos que as luzes deixem de piscar

That is grammatical and natural.
However, parar de piscar is very straightforward and common.

Very roughly:

• parar de = stop
• deixar de = cease/stop

In many everyday contexts, both work.

The comma separates the main command from the following clause:

• Espera,
• a menos que as luzes parem de piscar.

It helps show the pause and makes the structure clearer: first the instruction, then the exception.

In English, you would also often write:

• Wait, unless the lights stop flashing.

So the punctuation works similarly here.