Why do the lenses in my glasses create a shadow?

Question

When I hold my glasses in the light, the lenses create a shadow, the aren't tinted, so I would think the light would pass through. But why does it make a shadow where the lenses are?

Answer 1

There are two different effects here. This first is that the glass in your lenses doesn't let all of the light through. Because of this, the area behind the lenses will appear darker--a shadow!

Another effect is that the lenses bend the light going through (refraction). This is part of the design and is what helps you see better-they help your eyes focus. But this means that the light that would end up opposite the lens can be diverted to areas further away. You might also see some brighter areas where the light is focussed by the lens. The specifics will depend on how far away the lens is from the surface where you see the shadow. They also depend on exactly what type of lens you need: do you have near-sightedness or far sightedness?

Answer 2

There are complete shadows (umbras) and partial shadows (penumbras). (Peninsular means almost an island, right?). If the lens can reduce the amount of light striking a surface either by absorbing, reflecting or diverging light, it will create a penumbra. An eclipse of the sun also can produce a complete or partial shadow depending on where the observer is standing. If you hold your glasses at arms length and move them while looking at objects in the distance the images will either expand or contract depending on whether you lenses bend light outward or inward. You can tell if a person is near or farsighted this way.

Answer 3

An object becomes more and more opaque (solid looking) if there are more surfaces for the light to bounce off of. Your glasses are most likely ground to fit your vision. The edges are usually cut using a rough scraper. But embedded in the glass are tiny particles of dust, pollutatant, or smudges on the glass. Whatever. As long as light finds something to whack, you see it better.

Answer 4

Not all the light gets through so you don't get a true shadow, just an area of less illumination.

Answer 5

because they do not transmit 100%of the light.