I was a shy child. Consequently, I spent a lot of time avoiding eye contact by looking down at the ground. All this time looking down at my feet allowed me to regard the ground upon which I was walking. Thus it was as a child that I first noticed the purple squares embedded in sidewalks.
Have you ever been walking in an older part of the city and noticed a checker board grid of purple squares under your feet?
No, they are not simply sidewalk decoration [wouldn’t that be nice?] but rather a system to illuminate spaces under sidewalks called areaways. Sidewalk prisms, also known as vault lights (or pavement lights in the UK), are glass prisms set into sidewalks in order to reflect the natural light from above, safely illuminating these subterranean spaces. [Why are they purple? The answer to that is at the end of the post].