# Talk:Diffuse reflection

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## Lambertian reflectance

In the article it says: "the reflected light will be evenly spread over the hemisphere surrounding the surface (2π steradians)."

Isn't the reflected light scattered according to uniformly distributed surface normal angle and thus the reflected photons are NOT equally distributed over the hemisphere surface? 80.221.29.165 (talk) 22:05, 9 October 2008 (UTC)

Not necessarily. See Lambertian reflectance and Lambert's cosine law. An ideal diffuse scatterer scatters light equally in all directions, without regard to the angle from the surface normal.--Srleffler (talk) 22:36, 9 October 2008 (UTC)
My point is, that if you shoot or reflect photons into random direction, equally in all directions, then the resulting distribution of photons in the hemisphere (photons/m^2) will not be evenly spread as the article says, but top of the hemisphere will be more densely populated than the sides. With ideal diffuse reflector, photons in a solid angle decreases as the cosine of an angle with the surface normal.80.221.29.165 (talk) 11:15, 10 October 2008 (UTC)
OK, you're right, and the article is poorly worded. What they were probably thinking of is that while the intensity (photons per steradian) falls off as cos(θ), the apparent brightness of the surface to an observer remains constant because the apparent area of the surface also falls off as cos(θ). More technically, the radiant intensity for an ideal Lambertian reflector is proportional to cos(θ), while the radiance is independent of θ. This article should probably describe Lambertian surfaces explicitly. They are a pretty important special case. Note that not all surfaces are Lambertian, however. In particular, for some surfaces the intensity falls off much slower than cos(θ).--Srleffler (talk) 15:52, 10 October 2008 (UTC)

## Proposed merge

I oppose the proposed merge with Scattering from rough surfaces. That article is on charged particle scattering. This article is on light. The subject matter is sufficiently distinct for two articles.--Srleffler (talk) 06:01, 13 July 2009 (UTC)

I also oppose it; and the editor who put the tags didn't even bother to put a rationale or start a discussion, so I'd say let's just take them away already. Dicklyon (talk) 02:58, 14 July 2009 (UTC)

## Light scattering

Editors of this article might be interested in the new article (possible content fork) Light scattering. It's possible that the two articles could be merged, although there may be merit in keeping them separate. Discussion at Talk:Light scattering.--Srleffler (talk) 16:53, 27 July 2009 (UTC)

It looks a lot broader than diffuse reflection. I don't like to see articles spring to life fully formed like that, and without URLs for the refs, but that's what we got. Dicklyon (talk) 06:12, 28 July 2009 (UTC)
Discussion is at Talk:Light scattering.--Srleffler (talk) 06:11, 29 July 2009 (UTC)

## Merge with Lambertian reflectance?

This article seems to cover very similar material to Lambertian reflectance to the point that they both use the same intro image. The difference seems to be in emphasis: this article focuses on the physics whereas Lambertian reflectance is primarily about modeling it in computer graphics. The fact that they are different articles seems to imply that they aren't the same thing. —Ben FrantzDale (talk) 13:41, 24 February 2011 (UTC)

Actually they are quite different things: diffuse reflection is the general phenomenon shown by almost any surface we see. Lambert's cosine law is the idealized angular behaviour we expect to find in an ideal, homegeneous, "featureless" surface, for example a white surface with very small, randomly oriented irregularities. Many (or most) diffusing objects are not Lambertian: see, for example, Oren–Nayar reflectance model, or, for celestial bodies, Geometric albedo. The figure here represents just an example (and includes also specular reflection). --GianniG46 (talk) 00:12, 25 February 2011 (UTC)
I agree with Gianni. This is an important point: one cannot assume all diffuse reflectors are Lambertian. It's an idealized model.--Srleffler (talk) 04:44, 25 February 2011 (UTC)

## Who the hell wrote this?

What is the exact mechanism of diffuse reflection? What happens to a photon when it strikes a surface? What causes the photon to reverse direction? Is it the electron, is it a force, is the nucleus?

Welcome to Wikipedia, the encyclopedia that anyone can edit. This article is written by many volunteers working collaboaratively. If you don't like the way an article is written, you are welcome to edit it and try to improve the style or content.
I think the problem is that you are looking for more details on the mechanism of reflection itself, rather than specifically the mechanism for diffuse reflection. Check out Reflection (physics) and see if it answers some of your questions. Particularly the section Mechanism. This article seems to me to provide pretty good information on the mechanism for diffuse reflection, presuming one already knows how reflection works.
Regarding the "aimed at children" comment: keep in mind that this is an encyclopedia, not a physics textbook. For topics that are not very specialized, a good article will have an introduction that is aimed at about the level of a smart 11 year old. A good article will cover topics of general interest first, and then move into more difficult or technical material further down in the body of the article, if necessary. Obviously, some topics demand a more advanced level of exposition than others. --Srleffler (talk) 16:28, 19 August 2012 (UTC)

## Vector Length in Figure 1

In the first paragraph it is said " An illuminated ideal diffuse reflecting surface will have ***equal luminance from all directions*** in the hemisphere surrounding the surface (...)". However, looking at Figure 1, the red arrows (that indicate diffuse reflection) have varying lengths. It can be confusing reading that and then seeing varying length vectors in Figure 1. I suggest to edit the figure in order to explain what the length of the red vectors mean (I personally do not do that because I am also confused .. :). Capagot (talk) 18:46, 10 October 2012 (UTC)

Done. The rays represent luminous intensity rather than luminance. --Srleffler (talk) 04:42, 11 October 2012 (UTC)

## Make it Clear the Light is not "Bouncing"

The wording of this article is technically correct, but does not make it sufficiently clear that photons involved in diffuse reflection are being absorbed and re-emitted. Many pop descriptions of diffuse reflection say incorrectly that light "bounces" off atoms. This is not true. All light involved in diffuse reflection is absorbed and (possibly) re-emitted. The non-absorbed light is scattered by either Thomson Scattering or Resonant Scattered. Either way it is absorbed and re-emitted. It does not "bounce" off the atoms. Thus, for a normal opaque, colored material, like an orange or a leaf, the light we see from the object is composed of newly-created photons, not the photons that originally impinged on the object to illuminate it. This should be made perfectly clear in the article so that there is no confusion about this. John Chamberlain (talk) 10:14, 10 April 2017 (UTC)