Which one is correct?!

English as a Second Language English Vocabulary, Grammar and Idioms
1

Fill in Past simple, past progressive or past perfect simple.

When i ---------(watch) TV the lights ----- (go) out.

Answer:

  • When i watched TV the lights were going out.
    Or
  • When i was watching TV the lights went out.

Am confused in the answer because at school the teacher explained this way to us.
(When) is one of the Past Continous tense keywords and he explained it in this way:

If (When) came in the first sentence then the verb after the pronoun should be in the 2nd form(past tense). and the verb that comes in the second sentence after the nound should be in past continous form.

For example:
When i watched TV, the lights were going out.
When: came in the first sentence.
i: the pronoun
watched: the verb after the pronoun (i)

The secone sentence: the lights were going out.
The verb that comes after the noun in the second sentence: were going(in the past continous form)

the lights: the noun.

2

When i was watching TV, the lights went out.

The teacher explanation sounds so complex that I can’t even understand it, but I think anyway that it isn’t true. Just think about the two actions. Here, the actions are (1) TV-watching and (3) lights-out. Which action happens suddenly in the middle of the other continuing action? The sudden action is simple past (the lights went out) and the continuing action is past progressive (I was watching TV).

If both actions are quick, then both are simple past: I watched her when she threw the frying pan.
If both actions generally continues together, then both are past continuous: I was washing the dishes while she was drying them.