louvers aren't designed for cutaway visors. The signal here is about 30 years old (LEDs are newer than the body), and the louvers look about 70 years old. They're horizontal for distance limiting.
louvers are those blinds put in the visors of some signals. Most are set vertically to blankout signals that are aimed at a skewed approach. They're a cheap way to visibly limit to a specific lane. When set horizontally they are used for distance limiting.
The top probably didn't have the louver. When you distance limit you want to blank out greens (and/or yellows) at closely spaced intersections so when you are at an intersection the nearby intersection signals appear blank. Then as you drive towards the nearby intersection the greens appear. Thats the point of limiting the distance.