Talk:Retroreflector

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Is retroreflection known to exist in any non-human artifacts, i.e. is it something that physical interactions and/or biological evolution could ever come up with? --Ryguasu 04:30 Feb 26, 2003 (UTC)

The eyes of, for example, a cat, I think. Not that this is an advantage for the cat, more a by-product of how the eye is built. - Patrick 10:05 Feb 26, 2003 (UTC)

Does this mean when the article says "Cat's eyes are retroreflectors in the road surface; although they stick out a bit you can drive over them", it's talking in a twisted way about feline eyes? I assumed "cat's eye" was maybe a britishism for those raised bumps they sometimes put on top of the middle line of a road. --Ryguasu 13:08 Feb 26, 2003 (UTC)

The ones in the road are named after the ones in the animal. - Patrick 13:14 Feb 26, 2003 (UTC)

However, retroreflective surfaces do not help pedestrians in the dark unless light is shining in the direction from which they are looking

This does not seem correct, I think this says light shining the pedestrian in the face, but it should be the opposite. - Patrick 18:26 Feb 26, 2003 (UTC)

I rewrote that sentence. I hope it makes more sense. -- Heron

[edit] Invisibility and retroreflection

Is this "invisibility cloak" really worth counting as a retroreflector? All that thing is is a slide projector. I don't see how it involves retroreflection any more than watching a movie in a theater. If you look at the way a retroreflector works, you can't use a retroreflector for this purpose because the projected light would go right back into the projector. Projection systems like this often do use screens with directional scattering to enhance the image brightness in a particular range of directions (toward the audience), but that's certainly not necessary and it's not the same thing as retroreflection. Tarchon 23:25, 20 May 2006 (UTC)

On the contrary, the invisibility cloak itself is made of retroreflective material. Nothing but a retroreflective material will work as the invisibility cloak. The projection system too is far more advanced than a simple slide projector. Please read the entire article starting at http://science.howstuffworks.com/invisibility-cloak.htm before making any changes -- Wikicheng 06:25, 22 May 2006 (UTC)

[edit] How well do they work at an angle?

I did some diagrams trying to figure out if retroreflectors really work at any angle. Short answer yes, long answer is they drop off to zero.

Here's a single trap in our retroreflector \/ taken from the whole retroreflector: \/\/\/\/\/\/\/

Now let's label the sides: L \/ R

Obviously when the light is coming straight down, side L's beams are reflected sideways into R and back out again. And R->L works the same way. Perfect.

  | |
  | |
L \-/ R

Now slightly shift the source of light beams to the left. Two things happen. First, L starts reflecting at a shallower angle and compresses into R's trough. Likewise, the tip of R starts radiating into space instead of hitting L. Both ways, the tip of R becomes less useful.

In the extreme example of just-shy 45 degrees, L becomes near-parallel to the light rays (effectively useless), and R is likewise reflecting nearly everything into space instead of back into the trap. (Then at 45 you hit a singularity, L becomes parallel and R becomes a perfect mirror.) Thus, I think you can say that Retroreflectors drop off to zero as you traverse 45 degrees in either direction from the normal. Since we are talking about limits I'm guessing it's logarithmic. More important, their effectiveness at steep angles is recovered by having deeper traps.

Basically my point is that retroreflectors are optimally used in straight-on situations. They offer a slight fudge factor over standard mirrors, but since this fudge-factor drops off rather quickly, a more proper term for these devices may be "diffuse mirrors." Broodlinger 05:01, 5 June 2006 (UTC)