Kada uključim veliko svetlo, u sobi više nema mraka.

This is about verb aspect.

• uključiti = perfective verb, meaning to switch on / turn on as a completed action
• uključivati / uključujem = imperfective verb, meaning to be switching on, to switch on repeatedly, or focusing on the process/habit

In the sentence Kada uključim veliko svetlo..., the speaker means:

• when I turn on the main light
• or whenever I turn on the main light

So Serbian uses the perfective present very naturally here.

A useful thing to know:

• after kada meaning when, Serbian often uses a present form of a perfective verb where English may use present or future-like meaning

Examples:

• Kada dođem, zvaću te. = When I arrive, I’ll call you.
• Kada uključim svetlo, sve se vidi. = When I turn on the light, everything can be seen.

So uključim is correct because it refers to the completed moment of turning the light on.

It can mean either when I turn on or whenever I turn on, depending on context.

In Serbian, kada + present can be:

• a specific future situation
• a general repeated situation

So this sentence could mean:

• When I turn on the main light, there is no more darkness in the room.
• Whenever I turn on the main light, there is no darkness in the room anymore.

Without more context, both are possible.

Literally, yes:

• veliko = big / large
• svetlo = light

But in everyday Serbian, veliko svetlo usually means the main room light or ceiling light, especially in contrast to:

• malo svetlo = a small light, lamp, dim light, bedside light, etc.

So this is a very natural expression, not a strange literal phrase.

Examples:

• Upali veliko svetlo. = Turn on the main light.
• Nemoj veliko svetlo, upali lampu. = Not the main light, turn on the lamp.

Because svetlo is a neuter noun here.

Serbian adjectives must agree with the noun in:

• gender
• number
• case

The noun svetlo is:

• neuter
• singular
• here in the accusative, which looks the same as nominative for neuter nouns

So the adjective must also be neuter singular:

• veliko svetlo

Compare:

• veliki sto = big table (masculine)
• velika soba = big room (feminine)
• veliko svetlo = big/main light (neuter)

Because u sobi expresses location, not movement.

With u, Serbian can take different cases:

• u + accusative = motion into something
• u + locative = being in something

Here, the meaning is in the room, so Serbian uses the locative:

• u sobi = in the room

Compare:

• Ulazim u sobu. = I am entering the room. → motion, so accusative
• Sedim u sobi. = I am sitting in the room. → location, so locative

That is why the sentence has u sobi.

Because nema is the natural Serbian way to say there is no / there isn’t.

• ima = there is / there are / has
• nema = there is no / there are no / doesn’t have

So:

• u sobi nema mraka literally means in the room there is no darkness

This is much more natural in Serbian than trying to build the sentence with nije.

Compare:

• Ima vode. = There is water.
• Nema vode. = There is no water.
• Ima problema. = There are problems.
• Nema problema. = There are no problems / no problem.

So nema mraka is standard and idiomatic.

Because nema requires the genitive case.

The noun is:

• mrak = darkness / dark

After nema, Serbian usually uses the genitive:

• nema mraka = there is no darkness

This is a very important pattern:

• ima vremena = there is time
• nema vremena = there is no time
• ima novca = there is money
• nema novca = there is no money
• ima svetla = there is light
• nema mraka = there is no darkness

So mraka is the genitive singular form of mrak.

Here više means no longer, any longer, or anymore.

So:

• više nema mraka = there is no more darkness
• more naturally in English: there isn’t any darkness anymore

Important: više has more than one meaning in Serbian.

It can mean:

1. more
   • više vode = more water
2. no longer / anymore when used in negative contexts
   • više ne radim tamo = I don’t work there anymore
   • više nema mraka = there is no more darkness

So the negative structure helps show that više here means anymore / no longer.

Yes, Serbian word order is fairly flexible.

The sentence:

• u sobi više nema mraka

could also be rearranged, for example:

• više nema mraka u sobi
• mraka više nema u sobi

But the original order is very natural because it first sets the location:

• u sobi = in the room

Then it gives the main statement:

• više nema mraka = there is no more darkness

So the sentence flows like:

• When I turn on the main light, in the room there is no more darkness.

Serbian often moves parts of the sentence around for:

• emphasis
• rhythm
• style

Even so, some orders sound more natural than others. The original is simple and idiomatic.

Yes. kad and kada both mean when.

In everyday speech:

• kad is very common and slightly shorter/more conversational
• kada can sound a bit more neutral, full, or slightly more formal, depending on context

So these are both natural:

• Kad uključim veliko svetlo, u sobi više nema mraka.
• Kada uključim veliko svetlo, u sobi više nema mraka.

The meaning does not really change.

Because Serbian usually does not need subject pronouns unless you want emphasis or contrast.

The verb form uključim already tells you the subject is I:

• uključim = I turn on / I switch on

So the pronoun ja is normally omitted.

You would add ja only if you want emphasis, for example:

• Kada ja uključim veliko svetlo, u sobi više nema mraka. = When I turn on the main light, there’s no darkness in the room. with extra emphasis on I

This is normal in Serbian:

• Radim. = I am working.
• Idemo. = We are going.
• Znaš. = You know.

They are related, but not always identical in tone.

• mrak = darkness / dark
• tama = darkness, often a bit more literary, abstract, or dramatic

In an everyday sentence about a room and turning on a light, mrak sounds very natural.

So:

• u sobi više nema mraka sounds ordinary and conversational

Using tama would be understandable, but it may sound more poetic or stylistically marked:

• u sobi više nema tame

That is why mraka is a very natural choice here.

Yes, in many contexts upaliti svetlo is actually extremely common.

Both can mean to turn on the light:

• uključiti svetlo
• upaliti svetlo

In everyday speech, many speakers often prefer:

• upaliti svetlo = turn on the light
• ugasiti svetlo = turn off the light

Meanwhile:

• uključiti / isključiti are also very common, especially with electrical devices in general

So you may hear:

• Kad upalim veliko svetlo, u sobi više nema mraka.
• Kad uključim veliko svetlo, u sobi više nema mraka.

Both are natural.