I just had a small question in the back of my head ever since I was a young kid. Even though I have been on UCP for a long while now, I never actually remembered to ask you guys as somone probably knows what i'm talking about.

Why is it that some car headlights have these small mould-like projections in them ? What are these and what do they do ? Are they restricted to some types of headlights (e.g glass) ? Are they a by-product of the manufacturing process and have no use ?