Die Lichtshow und die Tonanlage laufen schon.

Because the subject is two things joined by und:

• die Lichtshow
• die Tonanlage

Each noun is singular by itself, but together they form a plural subject, so the verb must also be plural:

• singular: Die Lichtshow läuft schon.
• singular: Die Tonanlage läuft schon.
• plural: Die Lichtshow und die Tonanlage laufen schon.

So laufen here is the 3rd person plural form.

Both nouns are feminine singular:

• die Lichtshow
• die Tonanlage

So each one takes the article die in the nominative singular.

This can be confusing because die is also the article for the plural in German. But in this sentence, each individual noun is still singular; the whole subject becomes plural only because they are connected by und.

They are in the nominative case because they are the subject of the sentence — they are the things doing the action of laufen.

A good way to spot this is to ask: What is already running / operating?
Answer: Die Lichtshow und die Tonanlage.

That makes them the subject, so nominative is used.

Not literally. German laufen often does mean to run or to walk, but it also has a broader meaning: to be running, operating, functioning, or underway.

In this sentence, laufen means something like:

• are already running
• are already operating
• are already on
• are already underway

This use is very common with:

• machines
• technical systems
• performances
• programs
• processes

So Die Tonanlage läuft can mean The sound system is running / operating.

Because in German, laufen is commonly used for things that are in operation or currently active.

For example, German speakers can say:

• Die Maschine läuft. = The machine is running.
• Das Programm läuft. = The program is running.
• Der Film läuft. = The film is showing.
• Die Show läuft. = The show is on / underway.

So with Lichtshow and Tonanlage, laufen sounds natural because both are things that can be active and functioning.

Here schon means already.

It suggests that the light show and sound system are active at this point, often with the idea that this may be earlier than expected or that the speaker wants to point out that the process has begun.

So the sentence has the sense of:

• The light show and the sound system are already running.

In other contexts, schon can have other meanings or tones, but here already is the straightforward one.

German adverbs like schon are often placed in the middle field of the sentence, which is the area after the conjugated verb in a main clause.

Here the structure is:

• Die Lichtshow und die Tonanlage = subject
• laufen = finite verb in second position
• schon = adverb

So:

• Die Lichtshow und die Tonanlage laufen schon.

This is completely normal German word order.

You could sometimes move schon for emphasis in other contexts, but this version is very natural and neutral.

Because German, like English, normally does not use a comma before und when it simply joins two nouns:

• die Lichtshow und die Tonanlage

A comma would only appear in other kinds of structures, not in a simple noun pair like this.

Both are compound nouns, which are very common in German.

• Lichtshow = Licht
  • Show
• Tonanlage = Ton
  • Anlage

A very important German rule is:

The last part of the compound determines the gender and grammatical behavior.

So:

• die Show → die Lichtshow
• die Anlage → die Tonanlage

That is why both compounds are feminine.

Also, the first part narrows the meaning:

• Lichtshow = a show involving light
• Tonanlage = an audio / sound system

Because in German, all nouns are capitalized, not just proper names.

So:

• die Lichtshow
• die Tonanlage

This is a standard spelling rule in German and helps you identify nouns more easily when reading.

Yes, you could say something like that in some situations, but it is not exactly the same in tone.

• laufen schon suggests they are running / operating / underway
• sind schon an suggests they are simply on

For technical equipment, an sein can work. But laufen often sounds more natural when you want to emphasize active operation, especially for systems, shows, or equipment that are functioning as part of an event.

So laufen schon is a good, idiomatic choice here.

Yes — then the verb would change to singular.

For example:

• Die Lichtshow läuft schon.
• Die Tonanlage läuft schon.

Because each of those subjects is singular, the verb is läuft.

With both together, it becomes plural:

• Die Lichtshow und die Tonanlage laufen schon.

That contrast is a useful pattern to remember.

No. German uses laufen in many wider senses than English run.

It can be used for:

• people moving on foot
• machines operating
• events or shows being underway
• films being shown
• software running
• processes continuing

So although English learners often first learn laufen = to run, its real range is broader. This sentence is a good example of that broader, idiomatic use.