Light Reflection: A 3D Designer's Guide

[Georges]

Light is Reflected from the surface of the object or pass through it(interior) and then the light is reflected ?

Sorry for my "noob" question i am a 3D designer just looking for some more knowledge

Thanks in advance

 

[kuruman]

H Georges and welcome to PF.

Some light is reflected at the surface and the rest is transmitted through the surface. If you stand in front of a store window, you see your reflection. That's the reflected light. Someone inside the store sees you through the glass. That's the transmitted light. Does this answer your question or did I miss your point?

On edit: I have ignored multiple reflections at the front and back surfaces of the glass.

 

[Georges]

Hello Kuruman

I am talking regarding reflection, both Specular or Diffuse, not refraction or absorption. I have seen some articles how light reacts with objects and they say that photons interact with atoms and then light is reflected. ( So light penetrates the objects goes through its interior(even a small amount) and then the light is reflected again ). So i am confused if light bounce of surfaces like a basket ball would do in a terrain or goes inside surface even a little bit interacts and then re - emitted
Thanks

 

[ZapperZ]

Light is Reflected from the surface of the object or pass through it(interior) and then the light is reflected ?

Sorry for my "noob" question i am a 3D designer just looking for some more knowledge

Thanks in advance

Your question doesn't have one unique answer unless you specify the range of wavelength AND the type of material.

From your description of your background, I will assume that you are talking about the reflection of visible light on a mirror surface. This then restricts the RANGE of wavelength or frequency of light being reflected, AND, focuses on reflectivity off of metallic surfaces. Here, the "free" or conduction electrons in the metal plays a major role in the reflection. It also means that this is a surface effect, because the skin depth of visible light on a metallic surface such as this is extremely small, the order of 10 nm.

There are other kinds of reflection on various material and for various wavelength that are not covered here, such as Bragg reflection. But this isn't what you are familiar with or encounter everyday.

Zz.

 

[sophiecentaur]

they say that photons interact with atoms and then light is reflected.

I wonder where you read that "they say". Do you have a reference? This is not what happens when light strikes most substances. Individual atoms in solids and liquids (dense matter) do not interact with individual photons. It is a bulk effect and the whole surface is involved; each photon interacts with the whole surface - unlike a tiny bullet would. (The stuff that we initially learn about Hydrogen Atoms and the way they absorb and re-emit single photons only applies when the atom is isolated in a gas). The very fact that we can make a shiny surface reflect light coherently to produce a sharp image must imply this. The whole of the incident wave interacts with the whole of the mirror and there is little to be gained by involving photons in an explanation. Gaseous atoms can absorb individual photons of the light and re-emit them at random times, destroying the coherence of any image.
The atoms near the surface work together to reflect, propagate and absorb the energy by various amounts, depending on the substance. The process is the same for specular or diffuse reflection but with many small facets, at different angles, a good image is not formed and you just get diffuse reflection.

 

[Georges]

well at first i though reflections happen on the surface of object. But after reading an article from 3D documentation i got cunfused, the article :
"""First, consider the diffuse interior. Incoming photons will enter the object, scatter around inside and either get absorbed or leave the object at another location.
If photons scatter many times, we get a diffuse appearance, due to photons leaving the surface in many different locations and directions."""

So they describe a scenario where the light pass through object and then the light is reflected again, (not surface reflection)i don't really want an in depth answer ... i just want to know a general rule like : some objects reflect from their surface (example : ) while others let light pass through em and then they reflect ( example skin? i guess)

Thanks

 

[Khashishi]

Right, some objects reflect at the surface and others let light penetrate some. Light will always penetrate a little bit into whatever it is reflecting off of, but for some materials (like metals) the distance is so short that for the purposes of design you can treat it as the surface.

Ceramics or stone are usually are somewhat translucent and often have a foggy look due to lots of subsurface scattering. The scattering will be usually be very diffuse. But if it's covered with glaze, then some light is reflected at the surface of the glaze, some at the surface between the glaze and the main material, and some makes it into the material and scatters around.

Skin is pretty translucent. Especially light skinned folks, you can often see their blood vessels and stuff through their skin.

Window glass has reflection from both the front and back side, so you can see a double image effect if you look carefully. Or even more images due to multiple reflections between the front and back, but this is hard to see without a laser.

 

[Georges]

Thanks for the nice answer guys i guess that answers my question :)

 

[sophiecentaur]

If photons scatter many times, we get a diffuse appearance, due to photons leaving the surface in many different locations and directions."""

Reflection is a Wave phenomenon. Photons are not little bullets and they don't bounce away from a glass surface. Photons are quantum particles and it is clear that you have the wrong model in your head about them. Stick to waves and that explains all you need to know about reflection, refraction and the rest.

 

[Khashishi]

Photons are not little bullets and they don't bounce away from a glass surface.

True, but ray optics is usually "Good Enough" for applications where the wavelength is much smaller than the size of the objects you are looking at. I assumed that when Georges said they were a 3D designer, they were talking about human architecture and not microchips.

 

[sophiecentaur]

True, but ray optics is usually "Good Enough" for applications where the wavelength is much smaller than the size of the objects you are looking at. I assumed that when Georges said they were a 3D designer, they were talking about human architecture and not microchips.

By that argument, we'd only need to use the Corpuscular theory - or why not the earlier Tactile theory?
Ray optics and the way it uses Snell's Law for calculating the angle changes relies on wave theory and not on Photon behaviour. Is there any point in trying to justify a dodgy approach just to avoid being 'wrong'?

 

[Khashishi]

Absolutely. It is justified because it is useful. The same way that Newtonian physics is useful.

 

[sophiecentaur]

Absolutely. It is justified because it is useful. The same way that Newtonian physics is useful.

Ray optics is not based on photons (predates it by generations). It was invented because 'rays' works. But it was used for refraction as well as reflection and bullets do not explain refraction. Waves do.