Learn Hardcore Romanian: În întuneric, lumina unui felinar este importantă. - In the dark, the light of a streetlamp is important.

In Romanian, when you express being in darkness as a general state, you use în + noun without an article. If you said în întunericul, it would mean “in the darkness” (a specific darkness already mentioned). So în întuneric corresponds to English “in darkness.”

Why do we say lumina and not lumină in lumina unui felinar?

In a genitive construction (X of Y), Romanian marks X, the possessed noun, with the definite article. Thus lumina = “the light”, and unui felinar = “of a lantern.” Literally it’s “the light of a lantern,” even if we don’t have a particular lantern in mind.

What is unui and why is it used before felinar?

Unui is the genitive/dative form of the indefinite article for masculine (and neuter) singular nouns. Here it turns felinar into “of a lantern.” The pattern is unui + noun to express possession or relation (genitive case).

Why is the adjective importantă feminine singular?

Adjectives in Romanian must agree in gender and number with the noun they modify. Since lumina (the light) is feminine singular, the adjective also takes the feminine singular ending -ă, giving importantă.

Could we use e instead of este in this sentence?

Yes. In informal speech or writing este often contracts to e:
În întuneric, lumina unui felinar e importantă.
Both forms are correct; e is simply less formal.

Is the comma after În întuneric mandatory?

The comma marks a pause after the fronted adverbial phrase “În întuneric.” It’s recommended for clarity, especially in longer sentences, but it isn’t absolutely required.

Could we say Lumina unui felinar este importantă în întuneric instead?

Yes. Romanian word order is fairly flexible. Placing în întuneric at the end yields:
Lumina unui felinar este importantă în întuneric.
You lose the slight emphasis on the setting, but the meaning stays the same.