Learn Hardcore Indonesian: Kami menyalakan senter kepala karena kabut turun lebih cepat daripada yang kami kira. - We turned on our headlamps because the fog came down faster than we thought.

Kami menyalakan senter kepala karena kabut turun lebih cepat daripada yang kami kira.
We turned on our headlamps because the fog came down faster than we thought.

kami suggests:

The speaker is talking about their group, and
The listener is not part of that group.

If you said kita menyalakan senter kepala..., it would imply that the listener was also there turning on headlamps, which is probably not the case in a typical narrative sentence like this.

What does menyalakan mean exactly, and how is it formed?

menyalakan means to turn on or to switch on (a light, a device, etc.).

Morphology:

Root: nyala = to be lit / to shine / flame / light (as a state)
meN- prefix: menyala = to be on / to be burning / to be lit
-kan suffix: menyalakan = to cause something to be lit → to turn something on / to light something

So:

Lampu menyala. = The lamp is on.
Saya menyalakan lampu. = I turn on the lamp.

In your sentence, menyalakan senter kepala = to turn on the headlamp(s).

Is senter kepala a normal way to say “headlamp”? Are there other options?

Yes, senter kepala is understandable and used in everyday speech. It literally means head flashlight.

Common options for headlamp / head torch:

senter kepala – very common, especially in casual speech.
lampu kepala – also possible; literally head lamp.
headlamp (pronounced like English, often in outdoor/technical contexts, especially in writing).

Word order:

In Indonesian, modifiers usually come after the noun.
So senter kepala = flashlight (for the) head, not kepala senter.

kepala senter would sound like the head of a flashlight, not a flashlight worn on the head.

So the sentence is natural: menyalakan senter kepala = turn on (our) headlamps.

Can karena go at the beginning, like in English “Because the fog…”?

Yes. You can say it in two main ways:

As in your sentence (reason at the end):
- Kami menyalakan senter kepala karena kabut turun lebih cepat daripada yang kami kira.
With the reason first:
- Karena kabut turun lebih cepat daripada yang kami kira, kami menyalakan senter kepala.

Notes:

When karena starts the sentence, a comma before the main clause is standard in writing.
Meaning does not change; only emphasis changes slightly:
- Original: focuses on the action (turning on headlamps) and then gives the reason.
- Reordered: emphasizes the reason first.

What does kabut turun literally mean? Why use turun for fog?

Literally:

kabut = fog / mist
turun = to go down / to descend / to come down

So kabut turun literally = the fog goes down or the fog comes down, but idiomatically it means:

the fog comes in / rolls in / descends

Indonesian commonly uses turun with weather-related phenomena:

hujan turun = rain falls / it rains
salju turun = snow falls / it snows
kabut turun = fog comes down / moves in

So kabut turun lebih cepat... is very natural Indonesian for the fog came in faster...

How does lebih cepat daripada work here?

lebih ... daripada ... is a standard way to form comparisons (X is more ... than Y).

Breakdown:

lebih = more / -er (comparative marker)
cepat = fast
daripada = than

So:

lebih cepat daripada = faster than

Other examples:

Dia lebih tinggi daripada saya. = He/She is taller than me.
Kota ini lebih besar daripada kota itu. = This city is bigger than that city.

In your sentence:

kabut turun lebih cepat daripada yang kami kira
= the fog came down faster than we thought

Why is yang used in daripada yang kami kira? What does it do?

yang here introduces a kind of relative clause or clause-like comparison.

Structure:

lebih cepat daripada yang kami kira
- literally: faster than that which we thought

Breakdown:

yang = links to an implied noun like the amount / speed / time.
kami kira = we thought / we expected.

So yang kami kira = what we thought or than we thought (it would be).

Without going too literal, it functions like English “than we thought”. Indonesian often needs yang to connect a comparison with a verb phrase:

lebih besar daripada yang saya bayangkan
= bigger than I imagined
lebih sulit daripada yang saya kira
= more difficult than I thought

So yang is grammatically needed there; you can’t normally say daripada kami kira alone in standard Indonesian.

What does kira mean here, and how is kami kira different from kami pikir or kami sangka?

kira means to estimate / to assume / to think (in the sense of “expect” or “guess”).

kami kira ≈ we thought / we expected / we guessed

Differences:

kami kira
Often about an expectation or estimate, sometimes proven wrong:
- Kabut turun lebih cepat daripada yang kami kira.
  The fog came down faster than we thought/expected.
kami pikir
More like we think in an opinion/mental sense:
- Kami pikir dia sudah pulang.
  We think he has gone home.
kami sangka
Often we assumed / we supposed, and quite often implies that assumption was wrong:
- Kami sangka hujannya akan berhenti.
  We assumed the rain would stop.

In your sentence, kami kira is the most natural for than we thought/expected about speed/time.

Could daripada be replaced with dari here? What’s the difference?

You will hear both in speech:

lebih cepat daripada yang kami kira (more formal/standard)
lebih cepat dari yang kami kira (very common in casual Indonesian)

In standard grammar:

daripada is preferred for comparisons (than).
dari is mainly from / of / since, but in actual usage, many people say lebih X dari Y.

So:

In careful/formal writing: daripada is safer.
In everyday conversation: dari is common and accepted.

Meaning does not change here; it’s a stylistic / register difference.

How do we know this sentence is past tense? Does Indonesian have past tense markers?

Indonesian verbs do not change form for past / present / future like English does.

The verb menyalakan stays the same regardless of time. The tense is understood from context or additional time words.

This sentence can mean:

We *turned on our headlamps…* (past)
We *turn on our headlamps…* (habitual/present)
We *will turn on our headlamps…* (future, if in a planning context)

If you really want to mark time explicitly, you add adverbs:

Tadi kami menyalakan senter kepala...
Earlier we turned on our headlamps...
Nanti kami akan menyalakan senter kepala...
Later we will turn on our headlamps...

In your example, English chooses past (turned on / came down / thought) because that’s the most natural interpretation, but Indonesian itself is neutral.

Is the whole sentence formal, informal, or neutral?

The sentence is neutral, natural standard Indonesian. It’s fine for:

Narration (stories, reports)
Conversation
Most kinds of writing

Some register notes:

kami vs kita: both are neutral; choice is about inclusion/exclusion, not formality.
senter is everyday, not very formal (in formal scientific writing someone might choose more technical terms, but senter is widely accepted).
The structure with karena, lebih ... daripada yang ... is standard and not slangy.

So you can safely use it in both spoken and written Indonesian.

Could this be said in a shorter or slightly different way that natives might also use?

Yes, several natural variations exist. Some examples:

Using dari instead of daripada (more colloquial):
- Kami menyalakan senter kepala karena kabut turun lebih cepat dari yang kami kira.
Using a noun perkiraan (estimate/expectation):
- Kami menyalakan senter kepala karena kabut turun lebih cepat dari perkiraan kami.
  = ...faster than our estimate/expectation.
Dropping kami the second time when context is clear:
- Kami menyalakan senter kepala karena kabut turun lebih cepat daripada yang dikira.
  ...than (we) thought.
  Here yang dikira is more vague/impersonal; often context shows whose thought.

All of these are natural; your original sentence is already correct and idiomatic.

Could kami be replaced with kita in this sentence, and what would that imply?

Grammatically, yes:

Kita menyalakan senter kepala karena kabut turun lebih cepat daripada yang kita kira.

This would be understood as:

We (including you, the listener) turned on our headlamps because the fog came down faster than we (you and I) thought.

So:

Use kami when your group does not include the listener.
Use kita when the listener is part of the group that did the action.

Which one you choose changes the social perspective, not the basic event described.