Una luce potente illumina la stanza.

Because luce is a feminine singular noun in Italian.

• un = masculine singular indefinite article
• una = feminine singular indefinite article

So you say una luce = a light.

A useful thing to remember is that grammatical gender in Italian does not always match natural gender. Even though light is not biologically female, luce is grammatically feminine.

You usually learn the gender together with the noun: la luce, not just luce.

In this sentence, you can also tell it is feminine because:

• the article is una
• the adjective is potente, which in this case works for both masculine and feminine singular, so the article is your clearest clue

A good habit is to memorize new nouns with their article:

• la luce
• la stanza
• il libro
• il tavolo

Potente means powerful, strong, or sometimes bright/intense depending on context.

In Italian, adjectives often come after the noun:

• una luce potente = a powerful light

That said, adjective position in Italian is flexible, and moving the adjective can sometimes change the tone or emphasis. The most neutral and common order here is noun + adjective.

So:

• una luce potente = normal, natural phrasing

Some Italian adjectives have the same form for both masculine and feminine singular.

Potente is one of those adjectives:

• potente = masculine singular
• potente = feminine singular
• potenti = masculine plural
• potenti = feminine plural

Examples:

• un motore potente
• una luce potente
• motori potenti
• luci potenti

So even though luce is feminine, potente stays potente in the singular.

Illumina is the third person singular present tense of illuminare = to illuminate / to light up.

Conjugation:

• io illumino = I illuminate
• tu illumini = you illuminate
• lui/lei illumina = he/she/it illuminates

In this sentence, the subject is una luce potente, which is singular, so the verb must also be singular:

• Una luce potente illumina...

Because Italian usually does not require subject pronouns when the subject is already stated or understood.

English often needs the subject:

• A powerful light illuminates the room

Italian can simply say:

• Una luce potente illumina la stanza

There is no need to add a separate word for it, because the subject is already there: una luce potente.

Italian uses articles more often than English does.

Here, la stanza means the room:

• la = the
• stanza = room

So the sentence is talking about a specific room, or at least presenting it as a definite room in the situation.

Italian often sounds incomplete without the article where English might omit it in other contexts. In this sentence, la stanza is the natural form.

Yes. In Una luce potente illumina la stanza:

• Una luce potente = the subject
• illumina = the verb
• la stanza = the direct object

The direct object is what receives the action.
The light is doing the illuminating, and the room is what gets illuminated.

Yes, but the neutral, standard order is:

Una luce potente illumina la stanza.

Italian allows more flexibility than English, so you could sometimes hear:

• La stanza è illuminata da una luce potente. = The room is illuminated by a powerful light.
• Illumina la stanza una luce potente. = more marked or literary, with emphasis on what is doing the action

For most learners, the original sentence is the best and most natural basic pattern to use.

Sometimes, but potente is usually better here.

• potente suggests something powerful, intense, strong in effect
• forte can mean strong, but with light it may sound less precise depending on context

So:

• una luce potente = very natural for a strong/powerful light
• una luce forte = possible in some contexts, but not always the best choice

Italian often has several possible adjectives, but one will usually sound more idiomatic in a given sentence.

It is pronounced approximately eel-loo-MEE-na.

A few helpful points:

• i at the start sounds like ee
• double ll is pronounced like a normal Italian l, but clearly
• stress falls on -mi-: illuMIna

So the full sentence sounds roughly like:

OO-na LOO-che po-TEN-te eel-loo-MEE-na la STAN-tsa

This is only an approximation using English spelling, but it can help at first.

Yes, stanza is a very common and basic word for room.

Examples:

• la stanza = the room
• una stanza = a room
• la mia stanza = my room

Depending on context, Italian can also use more specific words:

• camera = bedroom / room
• salotto = living room
• ufficio = office

But in a general sentence like this, stanza is perfectly normal.

The structure is:

article + noun + adjective + verb + article + noun

More specifically:

• Una = indefinite article
• luce = noun
• potente = adjective
• illumina = verb
• la = definite article
• stanza = noun

So it is a very useful model for beginners: A + noun + adjective + verb + the + noun

You can build similar sentences like:

• Una voce calma riempie la sala.
• Un suono forte sveglia il bambino.
• Una lampada piccola illumina il tavolo.