Learn Hardcore Spanish (Latin America): Cambié el foco de la sala porque estaba quemado. - I changed the light bulb in the living room because it was burnt out.

Here, foco means a lightbulb. That meaning is very common in much of Latin America (especially Mexico, Central America, Peru, Bolivia, parts of Ecuador and Argentina). Other regional words:

bombillo: Colombia, Venezuela, Dominican Republic
ampolleta: Chile
lamparita/bombita: Argentina and Uruguay (colloquial)
In Spain, people usually say bombilla

Why is there an accent on Cambié?

Cambié (with an accent) is the first-person singular of the preterite: I changed. Without the accent, cambie is a different form (present subjunctive or formal command: that I/he/you change), so the accent distinguishes the tense and meaning.

Why is the subject yo omitted?

Spanish usually drops subject pronouns because the verb ending already shows the subject. Cambié clearly means I changed. You can say Yo cambié for emphasis or contrast.

Why preterite cambié but imperfect estaba? Could I use estuvo?

Cambié is preterite because it’s a single, completed action.
Estaba is imperfect because it describes a background state (the bulb’s condition) and gives the reason.
Estuvo is possible but unusual here. It highlights a bounded, completed state, e.g., El foco estuvo quemado todo el mes (it remained burnt out for a set period). In a causal clause with porque, the imperfect (estaba) is the natural choice.

Could I say porque se quemó instead of porque estaba quemado?

Yes.

Porque estaba quemado focuses on the state: it was burnt out.
Porque se quemó focuses on the event: it burned out (at some point).
A very natural variant in everyday speech is Porque se me quemó (el foco), using se me to indicate an unintentional event that affected the speaker.

How do we know estaba quemado refers to the bulb and not the living room?

Agreement and logic. Quemado is masculine singular, matching el foco (masculine). La sala is feminine, so if it referred to the room, you’d expect estaba quemada—and semantically, a room being literally burned is unlikely in this context.

Would it change to quemada if I said bombilla or ampolleta?

Yes. The past participle-adjective agrees in gender and number:

la bombilla/la ampolleta/la lamparita estaba quemada
los focos estaban quemados

Why estar and not ser with quemado?

Use estar for conditions or resulting states. Estar quemado = to be in a burnt/burnt-out state. Ser quemado is not used for this meaning and can have unrelated or slang senses in some contexts.

Is de la sala better than en la sala? What’s the difference?

El foco de la sala identifies which bulb (the living-room one), like “the living-room bulb.”
El foco en la sala locates the bulb (or the action) in the living room.
Both are acceptable. If you’re distinguishing one bulb from bulbs in other rooms, de la sala is a bit more natural.

What would people say in Spain?

Most would say: Cambié la bombilla del salón porque estaba fundida.

bombilla = lightbulb
salón = living room
fundida is the common way to say a bulb is burnt out in Spain (rather than quemada).

Can I say cambié la luz?

It’s understandable but can be ambiguous, since luz often means light/lighting or electricity. For a bulb, prefer cambié el foco/la bombilla/la ampolleta, depending on the region.

Do I need a pronoun like lo in Lo cambié?

Not if you’re naming the object: Cambié el foco…
If the object is already known and you don’t repeat it, then use the pronoun: El foco estaba quemado, así que lo cambié.
Spanish generally doesn’t double a direct object like this with an inanimate noun.

Can I put the reason first?

Yes. Add a comma: Porque estaba quemado, cambié el foco de la sala.
Alternatives: Como estaba quemado, cambié… or Ya que estaba quemado, cambié…

When do I use porque vs por qué vs porqué vs por que?

porque = because: Lo cambié porque estaba quemado.
por qué = why (questions): ¿Por qué lo cambiaste?
porqué = the reason (a noun): No entiendo el porqué.
por que = “for which/that” (rare; usually por la que): La razón por la que lo cambié…

What if there are multiple bulbs in the living room?

Specify number:

Cambié los focos de la sala (all of them)
Cambié uno de los focos de la sala (one of them)
Cambié un foco de la sala (a bulb in the living room; could be read as “one of them,” but less explicit)

Could I use reemplazar or sustituir instead of cambiar?

Yes: Reemplacé/Sustituí el foco… These are a bit more formal/technical. Cambiar is the everyday verb most people use for swapping a bulb.

What’s the difference between apagado and quemado for lights?

apagado = off (but not broken)
quemado/fundido = burnt out (broken)
Also, se fue la luz = the power went out (a blackout), not a burnt bulb.

Could I use the past perfect: porque se había quemado?

Yes. Cambié el foco… porque se había quemado emphasizes that the burning-out event happened earlier than the changing. It’s a bit more explicit about sequence than porque se quemó and more event-focused than porque estaba quemado.