They’re just regular (prescription) glasses. The sky looks normal through them. What’s the deal?
Most likely uv protective coating.
Any coating might produce this through reflective destructive interference.
True but where I live in CA this would likely be the coating selected by the majority of people.
This is because your friend is a wizard, and their personal objects pick up a magical blue-purple hue the more they are handled. This is a gradual process, so it’s not noticeable on most of their things, but they wear their glasses every day so they pick up the hue at a steady rate.
Some coating on the glass is very faintly purple. Could be UV protection, anti glare, anti fog, etc.
Glass itself is very faintly green, so it’s not the color of the glass, unless they are made out of some other material (something like polycarbonate or sapphire).
Just to be pedantic, it’s not that the coating, itself, has any color; it’s usually clear, actually. The color shift is caused by the glass and the coating having different refractive indexes, causing the light to split up slightly as it reflects off the lens. Kinda like an oil slick on the street reflecting bright greens and purples that aren’t actually there.
I mean, can you really say that something doesn’t have a colour if you see it as that colour? Does it really matter that the colour is coming from different refractive indexes rather than that wavelength not being absorbed by the material? If it consistently happens in that set of circumstances, isn’t it fair to say that is its colour? I.e. the coating, oil slicks
Here’s the thing: if you change the thickness of the layer then the colour will change along with it, but the material is otherwise the same. This occurs because the layers produce a phenomenon known as thin film interference. So it’s not the material of the coating layer that produces the colour, it’s the interaction between two layers.
Anyway, you can see all of the colours of a light’s spectrum through a prism but you wouldn’t say the prism itself is any of those colours. It’s transparent and refractive. That’s all we have here with the glasses: refraction and reflection, with interference of certain wavelengths due to the exact thickness of the layers.
