La lumigo ĉe la kuliso ŝanĝiĝis.

Lumo means light itself.

Lumigo means lighting / illumination: the lighting as an effect, setup, or result of giving light. In a stage or scene context, lumigo often sounds more natural than lumo if you mean the lighting arrangement rather than just the physical light.

So the difference is roughly:

• lumo = light
• lumigo = lighting, illumination

Usually lumigo is better here.

• lumigo often refers to the lighting as a whole, or to the result/state
• lumigado emphasizes the ongoing process of lighting something

So:

• lumigo = the lighting
• lumigado = the act/process of lighting

In this sentence, the idea is that the lighting changed, not that the process of lighting changed while it was happening, so lumigo fits well.

Ĉe means something like at, by, near, or in the area/context of.

It is a fairly broad location word. Here it connects the lighting to the place or stage element named by kuliso.

Why not some other preposition?

• en would mean in/inside
• sur would mean on
• apud would mean next to
• ĉe is looser: at/by/in the area of

So ĉe is a natural choice if the idea is simply location or association.

Kuliso is a theater word. It usually refers to a wing, side piece of scenery, or a stage flat/backdrop element, depending on context.

So it is not everyday furniture or architecture vocabulary; it belongs especially to stage and performance language.

Because theater terms do not always match English one-to-one, the best English equivalent depends on the situation.

Because both nouns are being treated as specific:

• la lumigo = the specific lighting being talked about
• la kuliso = the specific wing/scenery element being referred to

Esperanto la works much like English the.

Also remember: Esperanto has no indefinite article. So there is no separate word for a/an.

Because kuliso is part of a prepositional phrase: ĉe la kuliso.

Here it is not the direct object of the verb, so it does not take the accusative -n.

The structure is:

• La lumigo = subject
• ĉe la kuliso = location phrase
• ŝanĝiĝis = verb

So kuliso stays without -n.

Because ŝanĝiĝis means that the subject underwent a change.

• ŝanĝis = changed something
• ŝanĝiĝis = changed, became different

In this sentence, the lighting itself is what changed. It is not changing some other object. So ŝanĝiĝis is the natural form.

Compare:

• La teknikisto ŝanĝis la lumigon. = The technician changed the lighting.
• La lumigo ŝanĝiĝis. = The lighting changed.

-iĝ- often gives the idea become, get, or undergo a change of state.

So:

• ŝanĝi = to change something
• ŝanĝiĝi = to become changed / to change

Then -is adds past tense:

• ŝanĝiĝis = changed / became different

This -iĝ- pattern is very common in Esperanto.

For example:

• ruĝa = red
• ruĝiĝi = to become red

Yes. Esperanto word order is fairly flexible.

For example, you could also say:

• Ĉe la kuliso la lumigo ŝanĝiĝis.

That would put more focus on the location first.

The original order is completely normal, though, and may feel a bit more neutral.

A helpful breakdown is:

• ŝ = English sh
• ĝ = the j sound in judge
• ŝanĝiĝis = shan-JEE-jis, with the stress on the middle syllable

More exactly, Esperanto stress is always on the second-to-last syllable, so:

• ŝan-ĝi-ĜIS? No
• The syllables are ŝan-ĝi-ĝis
• Stress falls on ĝi: ŝan-ĜI-ĝis

The other main words are:

• lumigo → lu-MI-go
• kuliso → ku-LI-so