Wood/Glass/Metal Can One-Way Glass Be Made With Projected Light?

[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.