(GOOD)冷蔵庫を閉めた（な）ら 電気が消えますか。 I cannot exaplain the difference usage in [tara] and [nara]
であれば is closely realted to なら.
nara is similar to -eba eba is used when PEOPLE do the actions or suggesting an action. tara is used in the other cases and to is used when the action is expected to happen, rather than use the english 'if' use 'when...'
KS - I added your comment as a "note" on the above...
I also thought -tara had a bit more "when" whereas -eba was a bit more if. 行ったら： when you go 行けば： if you go although there is much more overlap than english
行ったら is more like "when you get there" and 行くなら would be "if you go." 行けば is either soft command or archaic "when you go."
なら is used in the context of suggestions, commands, violitional sentences and such. (One example of each above ;-)
Therefore なら can't be used in sentences like the following where no such elements are present. (BAD) 冷蔵庫を閉めるなら電気が消えますか。 (GOOD) 冷蔵庫を閉めると電気が消えますか。 If(when) you shut the fridge does the light go out?