Learn Hardcore Japanese: asa ha heya ga akarui node, denki wo kesite mo miemasu. - In the morning the room is bright, so I can see even if I turn off the light.

In this sentence, 朝は sets “morning” as the topic. The particle は indicates what the sentence is about. It doesn’t mark the subject performing an action, but rather introduces “the morning” as the time frame for what follows.

Why does 部屋 use が instead of は?

The particle が marks the grammatical subject of the descriptive clause “部屋が明るい” (the room is bright). If you used は, it would imply a contrast or emphasis (e.g. “as for the room, it is bright (but something else isn’t)”). Here you’re simply stating new information about the room’s brightness, so が is appropriate.

What does ので mean, and how is it different from から?

Both ので and から mean “because/since,” giving a reason.

ので is slightly more formal/soft and emphasizes a logical relationship; often used in written or polite contexts.
から is more direct and colloquial.
You could say 部屋が明るいから without changing the core meaning, but ので sounds softer and more explanatory.

What does 消しても express here, and how is it formed?

消しても comes from the verb 消す (to turn off) in its ‑て form () plus the particle , forming the “even if” conditional.Structure: Verb-て + → “even if you [verb].”So means “even if (you) turn off the lights.”