Learn Hardcore Finnish: Illalla tulee hämärä, ja sytytän taskulampun. - In the evening it gets dim, and I turn on the flashlight.

Illalla is ilta in the adessive case (ending -lla/-llä). One of the main uses of the adessive is to talk about time, especially meaning at / in (a part of the day).

So:

ilta = evening (dictionary form)
illalla = in the evening / at evening

Other common time expressions work the same way:

aamu → aamulla (in the morning)
päivä → päivällä (in the daytime)
yö → yöllä (at night)

So Illalla at the start of the sentence sets the time frame: In the evening.

Why is it tulee hämärä and not something like on hämärää?

Both are possible, but they say slightly different things.

Illalla tulee hämärä
Literally: In the evening, the twilight comes.
Meaning: Evening is when the dusk/fading light arrives / falls.
Focus: a change or onset – when dusk appears.
Illalla on hämärää
Literally: In the evening, it is dim.
Focus: a state – evenings are dim.

So:

tulee hämärä = the dimness/twilight arrives, starts
on hämärää = it is dim (describing what it’s like then)

The original sentence emphasizes the coming of dusk in the evening, not just the general fact that evenings are dim.

Is hämärä here a noun or an adjective?

Hämärä can be both in Finnish:

As an adjective: dim, dusky
- hämärä huone = a dim room
As a noun: dusk, twilight, semi-darkness
- Hämärä tuli nopeasti. = Dusk fell quickly.

In Illalla tulee hämärä, hämärä behaves like a noun:

It’s in the nominative singular (basic form).
It’s the subject of the verb tulee (comes).

So the structure is roughly:
[Illalla] [tulee] [hämärä].
In the evening comes the dusk.

Why does tulee (present tense) talk about something that happens in the future (later in the evening)?

Finnish does not have a separate future tense like English.

The present tense in Finnish is used for:

present time
regular habits
future events (when context makes it clear)

So:

Illalla tulee hämärä.
= It will get dark in the evening / Dusk comes in the evening.
Huomenna sataa.
= It will rain tomorrow.

English uses future forms (will come, will be), but Finnish stays in the present and lets the time expression (illalla) show that it refers to the future.

What is the subject of tulee in Illalla tulee hämärä? There is no “it”.

The subject is hämärä.

Finnish often puts place or time expressions at the beginning, and the subject can come later:

Illalla tulee hämärä.
Time: Illalla (in the evening)
Verb: tulee (comes)
Subject: hämärä (the dusk)

There is no dummy subject like English it. English: In the evening *it gets dark.
Finnish: *Illalla tulee hämärä.
Literally: In the evening comes the dusk.

So grammatically:

Subject = hämärä
Verb (3rd person singular) = tulee

Could you also say Illalla tulee hämärää (with hämärää in partitive)? What’s the difference?

Yes, Illalla tulee hämärää is also possible, and it slightly changes the nuance.

Illalla tulee hämärä.
hämärä = nominative (complete, countable-like)
Focus: the appearance of dusk as a whole, the event of dusk coming.
Illalla tulee hämärää.
hämärää = partitive (incomplete, unbounded)
Focus: some dimness develops / a bit of dusk appears, more like a gradual or ongoing process, not a complete event.

In everyday speech, many learners may just use one or the other, but native speakers feel:

nominative = more event/completion
partitive = more process/amount/atmosphere

Why is there a comma before ja in Illalla tulee hämärä, ja sytytän taskulampun?

In Finnish, you normally put a comma between two independent clauses, even when they are joined by ja (and).

Here we have:

Illalla tulee hämärä. – a full sentence
sytytän taskulampun. – also a full sentence (verb + subject in the ending)

Since both parts could stand alone as sentences, Finnish writing usually separates them with a comma:

Illalla tulee hämärä, ja sytytän taskulampun.

In English, you usually do not add a comma before and in such a simple sentence, but Finnish punctuation rules are different here.

What is the subject of sytytän? There is no pronoun like “I”.

In Finnish, the personal ending on the verb shows the subject.

sytytän
stem: sytyttä- (light, switch on)
ending: -n = I (1st person singular)

So sytytän means I light / I turn on.
The -n ending tells you the subject is minä (I), so the pronoun is usually omitted:

(Minä) sytytän taskulampun.
= I turn on the flashlight.

The sentence doesn’t need a separate word for I.

Why is taskulampun with -n at the end instead of just taskulamppu?

The base word is taskulamppu = flashlight (literally pocket-lamp).

In sytytän taskulampun, taskulampun is the object of the verb sytytän, and it is in the genitive/accusative form (ending -n):

taskulamppu → taskulampun (genitive singular)

This ending is used for a “total object”:

The action is seen as complete.
The object is affected as a whole (you fully turn the flashlight on once).

Compare:

Sytytän taskulampun.
= I will (fully) turn the flashlight on.
Sytytin taskulampun.
= I turned the flashlight on (completed action).
Sytytän taskulamppua.
= I am in the process of turning on the flashlight / working on it (activity, not seen as completed) – rarer and sounds a bit odd here, but grammatically shows the idea: partitive object → ongoing/incomplete.

So taskulampun (with -n) matches a complete, goal-oriented action: I turn the whole flashlight on.

Is taskulamppu one word or two words (tasku lamppu)?

It is one compound word: taskulamppu.

tasku = pocket
lamppu = lamp

In Finnish, compound nouns are usually written as one word, and the grammatical endings go only at the end:

basic form: taskulamppu (flashlight)
genitive (here, as object): taskulampun
partitive: taskulamppua
inessive: taskulampussa (in the flashlight), etc.

You cannot write tasku lamppu as two separate words when you mean “flashlight”.

Could the word order be Hämärä tulee illalla, ja sytytän taskulampun? Does that change the meaning?

Yes, you can say:

Hämärä tulee illalla, ja sytytän taskulampun.

The basic meaning is the same (Dusk comes in the evening, and I turn on the flashlight), but the emphasis shifts slightly:

Illalla tulee hämärä…
Emphasis on the time: In the evening, (what happens?) dusk comes…
Hämärä tulee illalla…
Emphasis on what happens or on hämärä: Dusk comes (when?) in the evening…

Finnish word order is fairly flexible. Moving elements to the beginning often changes focus more than it changes literal meaning. Both versions are correct.