What is the importance of putting a mirror on the balcony window facing the street in geomantic omen?

Generally speaking, mirrors are reflective, and this property is used in Feng Shui to deal with evil spirits and prosperous wealth.

There are three kinds of mirrors, 1, flat mirror, 2, convex mirror, 3 and concave mirror.

See what you see. Usually, flat mirrors and convex mirrors are used to block evil spirits, and concave mirror is lucky.