Learn Hardcore Polish: Zapalam lampę w pokoju, kiedy jest ciemno. - I turn on the lamp in the room when it is dark.

Zapalam is 1st person singular, present tense, imperfective of zapalać – “I light / I turn on (habitually / right now).”
Zapalę is future tense, perfective of zapalić – “I will light / I’ll turn on (once, a single action).”
In this sentence you’re describing a habit (“when it is dark, I (always/usually) turn the lamp on”), so Polish uses the imperfective present: zapalam.
If you said zapalę lampę w pokoju, kiedy będzie ciemno, it would sound more like a single future event: “I’ll turn on the lamp in the room when it gets dark (on that occasion).”

Why is it lampę and not lampa?

The base form is lampa (feminine noun, nominative singular).
In the sentence, lampa is the direct object of the verb zapalam – “I turn on the lamp.”
Direct objects of most feminine -a nouns go into the accusative singular, which changes -a → -ę:
- lampa → lampę
- kobieta → kobietę
- kawa → kawę
So zapalam lampę literally = “I light (the) lamp.”

Why is it w pokoju and not w pokój?

w can take either locative (static “in”) or accusative (movement “into”), depending on the verb and meaning.
With a location, no movement – “in the room” – Polish uses locative:
- pokój (nominative) → pokoju (locative) → w pokoju = “in the room.”
w pokój (with accusative) is rare and would normally imply movement into the room, and even then Poles usually say do pokoju for “into the room”:
- Idę do pokoju – I’m going into the room.
In the sentence there is no motion; the lamp is simply located in the room, so you need w pokoju.

Why do we use jest ciemno and not something like jest ciemny?

ciemny is an adjective (“dark”) and normally needs a noun:
- ciemny pokój – a dark room
- ciemne niebo – a dark sky
ciemno here is an adverb-like predicative word. In Polish, descriptions like “it is dark / cold / late” usually use these adverb forms:
- jest ciemno – it is dark
- jest zimno – it is cold
- jest głośno – it is loud
- jest późno – it is late
So the structure jest + ciemno is how Polish normally says “it is dark” in a general, impersonal way.

What exactly does jest ciemno mean? Is there an “it” in Polish?

English has a dummy subject “it” (it is dark, it is raining).
Polish usually doesn’t use a separate “it” here; the verb alone covers it.
jest ciemno literally is “is dark(ly)” but is best understood as “it is dark” / “there is darkness.”
Similar patterns:
- Jest gorąco – It is hot.
- Jest jasno – It is bright.
- Jest wcześnie – It is early.

Why is there a comma before kiedy?

kiedy (“when”) introduces a subordinate clause (kiedy jest ciemno).
Polish punctuation rules require a comma before most subordinate conjunctions, including kiedy, gdy, bo, że, etc.
So both variants need a comma:
- Zapalam lampę w pokoju, kiedy jest ciemno.
- Kiedy jest ciemno, zapalam lampę w pokoju.
In English you can often drop the comma, but in Polish you must keep it here.

Can I change the word order? For example: Kiedy jest ciemno, zapalam lampę w pokoju?

Yes.

Both are correct and mean the same thing. Differences:

Starting with kiedy jest ciemno puts a little more emphasis on the condition (“When it is dark, that’s when I…”).
Starting with zapalam sounds slightly more neutral and “statement-like.”

Word order is fairly flexible in Polish; you mainly have to be careful with stress or emphasis, not with grammar.

Does zapalam mean “I light” or “I am lighting”? How do I say the progressive?

Polish doesn’t have a separate progressive tense like English “I am lighting.”
zapalam can mean both:
- Right now: “I am lighting / I am turning on (now).”
- Habitual: “I (usually) light / I (always) turn on.”
The context kiedy jest ciemno (“when it is dark”) makes it clear that this is about a repeated habit, so we translate it as “I turn on the lamp in the room when it’s dark.”
If you really want to stress “right now,” you might add a time adverb or phrase:
- Teraz zapalam lampę – I am lighting the lamp now.

Could I say włączam światło instead of zapalam lampę?

Yes, and it’s actually more typical in everyday speech.

zapalam lampę – literally “I light the lamp,” slightly more literal or old-fashioned, also used for physical flames (candles, matches).
włączam światło – “I turn on the light” (with electricity, switches).
A very natural everyday sentence would be:
Włączam światło w pokoju, kiedy jest ciemno. – I turn on the light in the room when it’s dark.

Your original sentence is correct; it just sounds a bit more “literal lighting” than “flipping a switch.”

Why don’t we say Ja zapalam lampę…? Where is the “I”?

In Polish, the verb ending -am already tells you the subject is “I” (1st person singular).
Because of that, the pronoun ja (“I”) is usually dropped unless you want to emphasize who is doing the action.
- Zapalam lampę – I turn the lamp on. (neutral)
- Ja zapalam lampę, nie on. – I turn the lamp on, not him. (contrast/emphasis)
So Zapalam lampę w pokoju, kiedy jest ciemno is the normal, natural form.

What case is w pokoju and how does pokój decline?

w pokoju is locative singular of pokój (“room”).
Masculine noun pokój declines like this (singular):
- Nominative: pokój – the room (subject)
- Genitive: pokoju – of the room
- Dative: pokojowi / pokojowi (less common form: pokojowi)
- Accusative: pokój – (I see) the room
- Instrumental: pokojem – with the room
- Locative: pokoju – in/about the room
- Vocative: pokoju! (rarely used)
After w with a static meaning “in,” you must use the locative → w pokoju.

Is there any difference between kiedy and gdy here?

In this context, kiedy and gdy are near-synonyms and both are fine:
- Zapalam lampę w pokoju, kiedy jest ciemno.
- Zapalam lampę w pokoju, gdy jest ciemno.
kiedy is slightly more colloquial and universal (“when”), also used in questions:
- Kiedy przyjdziesz? – When will you come?
gdy is often felt to be a bit more formal or literary, and it’s not used in direct questions.
For everyday speech in your sentence, kiedy is perfectly natural.