the rooms were really dark and it was different to take phot

这个问题可以看出,你很善于动脑——这是成功者必备的素质之一.
这里,it是【形式主语】,这时,经常用来代替从句、动名词、不定式短语等所做的主语.
这个句子中,it就是代替不定式短语【 to take photos】来做形式主语.即：
to take photos was different .
但是,英语习惯把真主语后置,前面用形式主语it,因此,也可以看做是固定句型.例如：
It is 【a good idea】 to go out for a walk after supper.
It is 【nice】 of you to help me.
It is 【suggested】 that we keep up till we have been successful.
祝你开心如意!

这里的it指的是前面the rooms were really dark 这一现象

it was 是形式宾语，有固定句型：it is／was 。。。to do。。。其中it is／was不能代替