Why Do One-Way Mirrors Fail At Night?

Factual Questions
1

I’m sure some SDoper knows the rule of thumb on this. When the lighting is equal on both sides of a one-way mirror, you can see through from either side, IIRC, with ease. I was wondering if the SDopers can confirm if this is correct, and are there are times* when this is true, and why?

*Other than walking close-up to it, shading your eyes, and peeping through, that is? And, overall, what rules of light (or mirrors) govern the one-way mirror?
Thanks,

  • Jinx
2

As a general rule, you can see through the mirror from the darker side to the lighter side. In situations where two-way mirrors are used, the observers generally are in dark or dimly-lit rooms while the room being observed is well-lighted. If you were to turn on a light in the observer’s room, the observees(?) would be able to see to the other side.

3

A regular mirror is completely reflective in one direction - almost all of the visible light that hits it is reflected back.

A two-way mirror is basically a lightly-silvered piece of glass. Only some of the light that hits it is reflected back to the viewer. If both rooms were lit equally, a person on each side could see the other side equally well. When stand in the dimly lit room, you can see the well-lit room, since some of the light will filter through. People on the other side can’t see in, since the dim room has less light to actually get through. The little that does get through washes out in the ambient glare.

When you cup your hands around your face to try to look through the mirror, you’re basically creating a situation where your side is as dim as the other side, giving you a chance to see what little light leaks through. If the other side is completely dark, you’re pretty much out of luck.

4

You don’t even really need special mirrors to see this effect. If you try to look out your windows at night, you will often see your reflection instead. Someone outside can see inside with no problem. If you turn off the lights, you can see outside just fine.

5

Good point - same effect at work. Same thing with super-dark limo windows. The couple of times I got to ride in one, it was a kick watching people try to see in the car. The inside of the limo was always dimly lit.