Learn Hardcore Swahili: Tazama dari; balbu moja imeungua tena. - Look at the ceiling; one bulb has burned out again.

tazama = look/watch, often a bit more formal or directive.
angalia = look at, pay attention to, check; very common in everyday speech. Plural imperative: tazameni / angalieni if addressing more than one person.

Does dari mean ceiling or roof?

dari is the ceiling (inside the room). The roof (outside of the building) is paa. So the sentence is pointing you to the ceiling, not the roof.

Could/should it be darini instead of dari?

Both are possible:

tazama dari = look at the ceiling (treats it as a direct object).
tazama darini = look on/at the ceiling area (uses the locative suffix -ni). In many contexts they’re interchangeable; -ni adds a more explicit sense of location.

Why is there a semicolon? Could I use something else?

A semicolon here links two closely related clauses. You could also use a comma or a period:

Tazama dari, balbu moja imeungua tena.
Tazama dari. Balbu moja imeungua tena. All are acceptable; the choice is stylistic.

What noun class is balbu, and how does that affect imeungua?

balbu is commonly treated as class 9 (singular) with class 10 (plural) having the same form balbu.
Class 9 subject agreement is i-, hence i-me-ungua = imeungua.
Plural agreement (class 10) is zi-: balbu mbili zimeungua (two bulbs have burned out).

Does moja take any agreement here?

With class 9 nouns like balbu, moja appears without a prefix: balbu moja. In other classes it can take a prefix, e.g., kitabu kimoja (one book, class 7).

Could I drop moja? What changes in meaning?

balbu imeungua tena = the bulb has burned out again (a specific bulb already known in context).
balbu moja imeungua tena = one bulb (of several) has burned out again; it emphasizes the number one.

What exactly does imeungua mean, and how is it built?

Structure: i- (class 9 subject) + -me- (perfect) + -ungua (burn, be burnt) → imeungua = has burned/burned out.
Note: kuungua is intransitive (be/get burned). The transitive causative is kuunguza (to burn something).

Why not imezimika or imezima instead of imeungua?

imeungua = the bulb has burned out (failed due to burning; needs replacement).
imezimika = it has gone out (e.g., due to power fluctuation), not necessarily broken.
imezima often means someone/something turned it off, or it went off; it doesn’t imply permanent failure.

What does tena do here, and where do I put it?

tena means again. It usually comes after the verb phrase: imeungua tena.

With negation, tena often means anymore: haiwaki tena (it no longer lights/doesn’t light anymore).
You can put Tena at the start of a sentence to mean moreover/again in discourse.

How would I say another/one more bulb has burned out?

Another bulb: balbu nyingine imeungua (class 9 adjective: nyingine).
One more bulb: balbu moja zaidi imeungua or balbu moja tena imeungua. All are idiomatic; zaidi is very common for more.

How would the sentence look in the plural?

Tazama dari; balbu mbili zimeungua tena. (Two bulbs have burned out again.)
With many/unspecified: Tazama dari; balbu nyingi zimeungua tena.

How can I make the command more polite?

Tafadhali angalia darini; balbu moja imeungua tena.
Je, unaweza kuangalia darini? Inaonekana balbu moja imeungua tena. You can also use the subjunctive: Naomba uangalie darini…

Any quick pronunciation tips for these words?

Swahili stress is on the second-to-last syllable: ta-ZA-ma, DA-ri, BAL-bu, i-me-un-GU-a, TE-na.
Roll or tap the r in dari lightly.
Say both consonants in balbu clearly; it’s two syllables: bal-bu.