Light Through Blinds
Blindsides bridge these gaps thereby eliminating the light.
Light through blinds. Consequently light creeps in down the sides. Similarly curtains often hang slightly away from the window frame. The mechanism of roller blinds in particular does not allow blackout fabric to stretch right to the edges of a window frame.
Roller shades naturally have large gaps to the sides of the fabric so these light blocking strips are the perfect solution for maximum light control.
Source : pinterest.com