I first noticed it on the xenon flash on my Nokia N8. When viewed from an angle you could easily see the glass on front of the flash tube which had clearly defined vertical cuts which made the glass look like its been made my gluing different glass shards.
Then I saw things called flash diffusers for hot shoe xenon flashes.
So why does flashes have diagonal cut patterns on their glasses and what are these flash diffusers? How it would look like if these patterned glasses and flash diffusers didn't exist?