I read the following sentence on the BBC Japanese site:


Until now I understood the -たら form only to mean "if", but the 見たら in this sentence indicates that the interviewee is saying "when (I) looked down instinctively".

I've found that the -たら ending can mean "if" and (a new meaning for me) "when", and which meaning to take depends on the context.

So...my question I guess is which part of the context should I be using to determine "if" or "when" is the meaning?

The only pattern I can see in other examples is that the past tense (here it's 見えた) ending of the entire sentence indicates "when", and a present/future tense for the entire sentence hints at the meaning "if".

Have I got this completely wrong...? :)