The primary objective of this study is to demonstrate using polysomnography (PSG) that 10 mg lemborexant is superior to zolpidem tartrate extended release 6.25 mg (Ambien CR®) on objective sleep maintenance as assessed by wake after sleep onset in the second half of the night (WASO2H) after the last 2 nights of treatment in participants 55 years and older with insomnia disorder.