Can One-Way Glass Be Made With Projected Light?

[DaveC426913]

Measure the length between the person (A)
( wants to see) and glass. It would be a tinted glass at the measurement somewhere in th middle of darkest and brightest. Depending on how far person A is from the glass.

Simplest way I can put it. Always better way

Sorry, Can you put it less simply?
How does the distance between a subject and the glass make a difference?
And what does 'somewhere in the middle of darkest and brightest' mean?

 

[phinds]

Sorry, Can you put it less simply?
How does the distance between a subject and the glass make a difference?
And what does 'somewhere in the middle of darkest and brightest' mean?

Yeah, @Marco Aquino I also didn't understand what you said. I think perhaps there's a language problem.

 

[DaveC426913]

I think perhaps there's a language problem.

Sure but, like a Universal Translator, if we get enough data, we can probably interpolate the meaning.

 

[sophiecentaur]

Sure but, like a Universal Translator, if we get enough data, we can probably interpolate the meaning.

Perhaps the Vogon version would be more understandable?

 

[DaveC426913]

I shall rend thee in the gobberwarts with my blurglecruncheon, See if I don't!

 

[sophiecentaur]

We shall be keelhauled by the constabulary if we veer off topic any more, I think.

 

[DaveC426913]

Think of it as doing our part to keep the thread at the top of New Posts until the OP returns.
There should be a Trophy for that!

 

[phinds]

I swear to Pete, you guys are going to reticulate my framis.

 

[sysprog]

. . . as in chiropractor. Etc etc

Right. The problem MDs in general have with chiropractors is the pseudo-scientific medical model set upon which the guild of chiropractic practicianship historically founded itself. I think that many MDs recognize that some chiropractors are very skilled at pain-alleviating manipulations.

 

[sysprog]

I shall rend thee in the gobberwarts with my blurglecruncheon, See if I don't!

Shades of Joyce!

 

[jim mcnamara]

Well, ReJoyce. You al have just ruined a thread. It goes down to GD where nonsense can roam free.

 

[Baluncore]

In this thread we have had tinted glass mentioned, but nowhere did I see mention of a Circularly Polarised film being used. CP film can be LH or RH, so half the random light gets in, half the random internal light gets out. But light that crosses the film is unable to return through the film because the polarisation is reversed by reflection.
Visual displays often have a thin film to prevent reflections from the external surface, they are also CP so you will not see your reflection in the display surface.

 

[sysprog]

In this thread we have had tinted glass mentioned, but nowhere did I see mention of a Circularly Polarised film being used. CP film can be LH or RH, so half the random light gets in, half the random internal light gets out. But light that crosses the film is unable to return through the film because the polarisation is reversed by reflection.
Visual displays often have a thin film to prevent reflections from the external surface, they are also CP so you will not see your reflection in the display surface.

I'm reminded of the little (maybe $\rm{1cm}$ diameter circular film area) card (maybe $\rm{3cm^2}$) card that came with cheap (around/maybe $5-$8) polaroid sunglasses in the mid-'70s -- you could rotate the card with respect to the sunglass lens and see the light go from sunglass-dark to almost completely dark $\dots$

Around 20 years ago I looked indignantly at a 20-something kid who was clerking in a sunglass/opticks ($\leftarrow$ Isaac Newton's spelling of the word which in (what IBM calls) US English would be spelled/spelt 'optics' -- Newton meant the principles more than the instrumentation -- I mean the gear/kit) shop at a mall -- he was pointing and telling regarding which sunglasses had polarized ($\leftarrow$ US English spelling) lenses -- I said that if he would please just hand to me a pair that he knew to be polarized, that I could rotate them and see for myself which of the sunglasses in the display case were or weren't polarized --

At first he just handed me the glasses and showed a bewildered look on his face -- then I handed him back the glasses and said hold up the glasses and look through them at that display case and rotate the glasses and you'll see which glasses have polarized lenses -- accordingly, he looked and he saw, and he gave a smile $\dots$

 

[Lewis Goudy]

Weeeelllll, it does exactly the opposite of what his diagram shows.

With one-way glass, the person in darkness can see the person in the lit room. Whereas the person in the lit room can't see the person in darkness.

Another example of an "optical diode" is a grid or screen which is close to the eye and distant from the object observed. Even after giving effect to the circumstance that the level of illumination in my office is likely twenty times greater than that of the roadway in front of my house, I can resolve quite clearly what the vehicle is, a truck or a jeep or pair of babes on bikes passing by, that one is cuter than the other--yet all they see looking my way is a window, perhaps make out that it is fitted with blinds rather than curtains. Even at dusk when it is actually brighter in my room than outside this remains the case; it is a matter of truncation of a cone of two nappes at different distances from the vertex.

 

[DaveC426913]

Another example of an "optical diode" is a grid or screen which is close to the eye and distant from the object observed. Even after giving effect to the circumstance that the level of illumination in my office is likely twenty times greater than that of the roadway in front of my house, I can resolve quite clearly what the vehicle is, a truck or a jeep or pair of babes on bikes passing by, that one is cuter than the other--yet all they see looking my way is a window, perhaps make out that it is fitted with blinds rather than curtains. Even at dusk when it is actually brighter in my room than outside this remains the case; it is a matter of truncation of a cone of two nappes at different distances from the vertex.

That is ... an astonishingly simple and elegant solution.

 

[Lewis Goudy]

That is ... an astonishingly simple and elegant solution.

https://www.physicsforums.com/attachments/248334

I said "optical" in haste but "visual" or perhaps "informational" or "cryptologic" would have been apter in some ways. There seem to be several perspectives of like applicability.

 

[sophiecentaur]

Even at dusk when it is actually brighter in my room than outside this remains the case;

The 'brightness' of the outside scene is less important than the 'brightness' of the reflected image that people outside can see. If the outer surface of the one way device is reflecting the sky - due to the tilt of the slats - then the brightness of the sky is what is seen and compared by the outside observer. The tilt of the slats gives the one-way effect without being so blatant as a mirror would.

Venetian Blinds are elegant because their effect can be controlled.

 

[Lewis Goudy]

The 'brightness' of the outside scene is less important than the 'brightness' of the reflected image that people outside can see. If the outer surface of the one way device is reflecting the sky - due to the tilt of the slats - then the brightness of the sky is what is seen and compared by the outside observer. The tilt of the slats gives the one-way effect without being so blatant as a mirror would.

Venetian Blinds are elegant because their effect can be controlled.

The babes on bikes are not seeing a reflected image when they look at my office window, but you are right about relative brightness and contrast having impedance-like characteristics. Suppose my blinds were two in number, with a one inch gap between them, of material whose albedo was zero. They wouldn't be dazzled (unless I invited them in for tea and tuppence). I was trying to say that apart from relative brightness if I stand close to a cheesecloth curtain I can see them well while they cannot see me at all.

 

[sophiecentaur]

The babes on bikes are not seeing a reflected image when they look at my office window, but you are right about relative brightness and contrast having impedance-like characteristics. Suppose my blinds were two in number, with a one inch gap between them, of material whose albedo was zero. They wouldn't be dazzled (unless I invited them in for tea and tuppence). I was trying to say that apart from relative brightness if I stand close to a cheesecloth curtain I can see them well while they cannot see me at all.

The "babes on bikes" are, of course seeing a reflected image (that by definition). It's just a diffuse image. When you look out of the window you see specific, well defined images and you can ignore a brightish sky but someone outside sees everything that's reflected off your window.
I hear what you are saying but the channel is totally reversible and the attenuation in both directions is the same. So it has to be down to 'some function' of the relative brightness of the two scenes. It's not just the exposure value that a camera would use.