La contaminación lumínica reduce la visibilidad.

Both contaminación and visibilidad are feminine singular nouns, so they take the feminine singular definite article la.

• la contaminación = the pollution
• la visibilidad = the visibility

A lot of Spanish nouns ending in -ción are feminine:

• la contaminación
• la información
• la situación

And many abstract nouns ending in -dad are also feminine:

• la visibilidad
• la ciudad
• la realidad

So in this sentence, la agrees with each noun in gender and number.

In Spanish, adjectives usually come after the noun they describe, especially in neutral, factual, or technical language.

So:

• contaminación lumínica = light pollution

This is the normal word order in Spanish. Putting the adjective after the noun is much more natural here than putting it before.

Also, lumínica agrees with contaminación, which is feminine singular, so the adjective is also feminine singular:

• lumínico → masculine singular
• lumínica → feminine singular

Lumínica means related to light. In this sentence, contaminación lumínica is the standard Spanish term for light pollution.

It does not mean that the pollution is literally shining. It means the pollution has to do with artificial light.

This is a good example of Spanish often using an adjective where English uses a noun:

• light pollution in English
• contaminación lumínica in Spanish

Reducir is the infinitive, meaning to reduce.

In the sentence, the verb is conjugated in the present tense to match the subject:

• reducir = to reduce
• reduce = it reduces / reduces

The subject is La contaminación lumínica, which is third person singular, so the verb must also be third person singular:

• La contaminación lumínica reduce...
• literally: Light pollution reduces...

Because in Spanish, the verb ending tells you who is doing the action.

For reducir in the present tense:

• reduzco = I reduce
• reduces = you reduce
• reduce = he/she/it reduces, or you (formal singular)
• reducimos = we reduce
• reducís = you all reduce (Spain)
• reducen = they reduce / you all reduce

So here, reduce matches la contaminación lumínica = it reduces.

The accent marks show where the stress goes.

• contaminación is stressed on the final syllable: con-ta-mi-na-CIÓN
• lumínica is stressed on the mí: lu-MÍ-ni-ca

Without the written accents, a Spanish speaker would stress them differently according to the usual spelling rules.

These accent marks are important because they tell you the correct pronunciation and sometimes distinguish between different word patterns.

In standard Spain Spanish, it is approximately:

la con-ta-mi-na-THYON lu-MEE-ni-ka re-DOO-the la bi-si-bi-li-DAD

A few key pronunciation notes:

• In much of Spain, c before i or e is pronounced like th in thin:
  • contaminación → ...na-THYON
  • reduce → re-DOO-the
• c before a, o, or u sounds like k:
  • lumínica → ...ni-ka
• v and b are pronounced very similarly in Spanish.
• The final stress in visibilidad is on -dad:
  • bi-si-bi-li-DAD

If you are used to Latin American Spanish, you may hear s instead of th in contaminación and reduce.

Spanish usually uses the definite article more often than English, especially with general concepts and abstract nouns.

So Spanish naturally says:

• La contaminación lumínica reduce la visibilidad.

Even though English often drops the, Spanish normally keeps it here.

This is very common:

• La música es importante. = Music is important.
• La educación cambia vidas. = Education changes lives.

So the articles in this sentence sound normal and natural in Spanish.

Visibilidad is an abstract noun, like visibility in English. Abstract nouns are often used in the singular because they refer to a general quality or condition.

So:

• la visibilidad = visibility in general

You would only use a plural form in special contexts where you are talking about different kinds or levels of visibility, which is not the usual meaning here.

Yes. Contaminación lumínica is the standard and most natural term.

You might also understand other phrases, but contaminación lumínica is the established expression used in everyday Spanish, journalism, education, and environmental topics.

So if you want to say light pollution, this is the phrase to learn.

Yes, that would also be correct.

Both verbs can work:

• reduce = reduces
• disminuye = decreases / reduces

The original sentence with reduce is very natural. Disminuye sounds slightly more formal or descriptive in some contexts, but both are good Spanish.

The structure is:

Subject + verb + object

• La contaminación lumínica = subject
• reduce = verb
• la visibilidad = direct object

So the sentence is very straightforward.

A literal breakdown is:

• La contaminación lumínica = The light pollution
• reduce = reduces
• la visibilidad = the visibility

This makes it a useful model sentence for learning standard Spanish word order.