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My Dad insists the it is possible to make a computer screen go silver, so silver that it turns into a mirror. I have tried to explain about pixels, but he doesn't understand it so how do I explain that a screen is light and you can't just make it shiny as it is emitting light, and well it just doesn't work.

So how do I explain how a screen works?

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After you have explained him you should use a webcam to create a fake mirror... ;-) –  Tom Wijsman Sep 3 '10 at 19:37
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A mirror needs more than the colour: en.wikipedia.org/wiki/Silvering –  Tom Wijsman Sep 3 '10 at 19:39
    
I told him about using a webcam but was still adamant you could make the screen silver. I also told him you just can't make the "colour" silver from light. He's bought Apple's "there's an app for that" too far as he thought someone could just make an app that rotated the pixels 180 degrees to show a silver surface :D It took a while for me to explain that wouldn't work anyway and that you can't just download hardware ;) –  Jonathan. Sep 3 '10 at 21:01
    
webcams make inverted mirrors :) which are real pictures as mirrors invert reality. –  laurent Sep 4 '10 at 3:22
    
Some webcam apps (Mac OS X Photo Booth) let the user switch from mirror to "actual" because most people are used to seeing their reflection rather than their actual appearance. –  Jared Updike Sep 4 '10 at 6:53
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Tell him it's like a TV. The screen itself has a light behind it, and the light is what makes the image. There are colored pixels in front of the light on the screen's surface which allow it to display images.

It won't work as a mirror since the screen surface is not reflective. It will display a silver color, but it is basically going to be a silver colored light.

You can't use a lightbulb as a mirror and you can't use a monitor as one either.

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Here's an analogy which may help: Slide projector! en.wikipedia.org/wiki/Slide_projector Images are between lightbulb and viewer. It's just that the wall is transparent. –  AndrejaKo Sep 3 '10 at 19:50
    
Good one @AndrejaKo! –  JNK Sep 3 '10 at 19:54
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Except for the glossy laptop screens. They act as mirrors already, under most circumstances (to the detriment of picture quality and your eyes). –  dbkk101 Sep 5 '10 at 18:06
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I think your dad is thinking of really old LCD displays. They had a mirror in the back, and if you made them all black, you'd allow light to pass to the back, you'd get a weak mirroring effect. Those days are well gone, and the mirrors are gone, replaced with backlights.

As an example, he no longer can play with the choke on his carburetor to help morning starts, tech has moved on to fuel injection, and no more mirrors.

If you really want to explain, get a flashlight, some colored plastic. show him how colors are made by shining the light through the plastic, and covering some of the plastic colors. or http://www.howstuffworks.com/lcd.htm

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Actually this happens in new "glossy" LCDs too. If I turn backlight off on my laptop, I can see myself clearly. If I turn off my laptop I can see myself clearly. Still, I don't believe that turning screen silver will actually help in creation of mirror effect. –  AndrejaKo Sep 3 '10 at 19:45
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What makes a mirror reflect images is not the color, it's the reflective substance on it. "simple" and antique mirrors were achieved polishing metal too and the reflection was due to the metalic shining.

To show him the color is not the responsible for the mirror effect, you can have 'mirrors' of different colors and other objects with the same color not reflecting images: usually some Christmas balls are reflective and in different colors - blue or red CD ROM (on the data side) too. The point of using silver is that it reflects almost all the colors so the image reflected doesn't miss colors. Colors are made by differences in light waves reflection (or absorbtion)(big simplification here - see colors) with white reflecting everything and black absorving anything. On a blue mirror, you won't be able to see the difference between the blue of the reflected image and the blue light (blue wavelenghs) due to the material properties of the mirror.

LCD monitors do not have this reflective layer (and are not made of polished metals) so they will never be mirrors. You can define their colors as perfect silver and they still will not reflect images. Basically they emit light, do not reflect. Proof of that is that when turned off (not emitting light) they are black so they absorb all light and do not reflect anything.

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Nice explanation. A few notes: some LCDs are made of polished glass (although not highly reflective metal). Also, LCDs have back lights that emit, but the actual liquid crystals absorb (various amounts of various wavelengths of some of) the light. And finally, older non-backlit LCDs (or e-ink, like an Amazon Kindle) have a diffuse silver back that doesn't absorb all light but since it's diffuse it reflects the light in different directions so it can't be a useful mirror. –  Jared Updike Sep 4 '10 at 6:50
    
@Jared - Thanks for the valuable complements and clarifications - its been a long time I was studying these things... I tried to make a simple abstract but I'm sure it's not very clear and complete as the subject is extense... :) –  laurent Sep 4 '10 at 16:11
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If you have a LiteBrite, it's real easy.

lite-brite

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this is actually a reasonable answer.. LCD are basically LiteBrites, are they not? –  Jeff Atwood Sep 4 '10 at 21:08
    
Not "real easy to make a mirror" but "real easy to explain pixels and how a computer screen could never be a mirror". Got it. –  Jared Updike Sep 6 '10 at 19:58
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The "trick" to having a mirror (beside turning off the self-illuminating parts of the CRT or LCD) is (1) high index of reflectivity (a number less than 100% for any two-material interface, but air and glass works fairly well) on a very flat surface (think glass or calm water) and (2) absorption or scattering of any unreflected light (think a heavily tinted car that you cannot peer into versus a non-tinted car window, or dark murky water vs shallow water where you can see the bottom). If you have a glossy screen iMac or iPhone (smooth glass) and you turn it off (black behind the glass) and the room has enough light or you are outdoors, the screen will be a mirror!

If you take a piece of glass and paint the back white, it will be pretty difficult to see reflections on it because (1) the white paint diffuses any transmitted light in many directions obscuring the reflected image in front and (2) glass/air isn't the most reflective surface (if it were highly reflective enough to make a mirror on its own we would never use it in automobiles). But if you paint a piece of glass black, it makes a decent mirror (in a well lit environment). (At my office we have one such black "whiteboard", the rest of the whiteboards are white (on the back) glass.)

Now take a piece of glass and vapor deposit aluminum on it (on the back so it won't scratch). (I did this in an Applied Physics class, not to make little mirrors, they were just a byproduct). Since aluminum is so reflective (see link) at visible light wavelengths, most of the light that enters the glass reflects off the back side when it hits the aluminum and returns to your eyes as a reflection. If you paint black behind the aluminum then you eliminate most stray diffuse/ambient light, which is more or less how standard household mirrors work.

So the "silver" paint is not just silver or light gray in "color" (a loaded word that's more complicated than we usually give credit for), the surface property is reflective (smooth like gold lamé) instead of diffuse (rough, like a yellow shirt---never to be mistaken for gold lamé no matter the color of yellow). Most of what we think of as every day "colors" (pigments) are diffuse.

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