Lam Rules
Lam of the Name اللَّه
Heavy when preceded by fatha or damma; light when preceded by kasra.
The lam in the name اللَّه (Allah) is unique: it is pronounced "thick" (mufakhkham) when preceded by a fatha or damma — قَالَ اللَّه (qaalAllah), هُوَ اللَّه (huwAllah) — and "thin" (muraqqaq) when preceded by a kasra — بِسْمِ اللَّه (bismillah). No other lam in Arabic has this dual treatment.