こん中だけ昼間になったぞ DB

Question

I'm still learning. This is Goku seeing artificial light for the first time in second chapter of DB. Translated as: "It's daylight in here!"

こん中 = この中 = in here

だけ = just

昼間に = daylight

なった = turned to

ぞ = emphasizer

I don't understand the nuance that だけ is adding to the sentence. There would be any difference in meaning if it is replaced by は?

Bulma had just turned on the lights. Is this だけ maybe referring to this fact but it got lost in the translation?.

Answer 1

This だけ means "only", and この中だけ means "only inside this (capsule house)". He said だけ because this light had its effect only within the capsule, which was surprising to him. Of course the real daylight normally fills the entire environment.

Note that English "just" has multiple meanings, and "just" as in "She had just turned on the light" or "I just started to eat" never translates to だけ. See this if you want to translate this type of "just".