Name: Elizabeth K.
How can you tell if a mirror is a "two-way" mirror?
A "two-way" mirror is just a mirror with little gaps in the shiny metallic
coating. Looking through a two-way mirror is like looking through a screen
with holes much smaller than usual. Light will pass through in both
directions. You can see through in either direction. The shiny coating is
visible from the front.
When looking at the front, the reflected light is MUCH brighter than the
little that comes through from the back. As a result, you don't notice it.
The back side is colored dark and dull. Very little light gets reflected
from the back. Someone behind a two-way mirror can see through more easily.
If you turn off ALL lights on the side in front of the mirror, make it pitch
black, you will be able to see through from the front. Of course, there has
to be a light on behind the mirror. Whenever a two-way mirror is used for
spying, the room behind the mirror is kept dark. This way, there is no
light to be seep through to the front. Also, the room in front of the
mirror is usually kept bright. This makes it easier for the "spies" to see
what is happening. It also makes it harder for the "victims" to notice any
light getting through the mirror.
I expect the first two-way mirror was just a cheaply made regular mirror:
the metal was not applied thickly enough to cover the glass well.
Dr. Ken Mellendorf
Two way mirrors work both ways. You can see through them best from the
dark side. If you are on the brightly lit side, and do not mind looking a
little weird, just press your cupped hands against the glass and press
your face against your hands so as to exclude as much light as possible
from your side. If there is much illumination at all on the darker side,
you should be able to see through. I did that once and discovered a
fellow on the other side watching me. We both broke up into laughter.
If you see a mirror hanging high on the wall of a department store, or
grocery store -- it is probably a two way mirror!
Seriously, if there is a light on the other side of the mirror, you will see
it from the other side because two-way mirrors transmit a part of the
incident light and reflect part of the incident light.
Two way mirrors let some light through in both directions. Just hold it
up to a light and if you can see through it it could function as a 2-way
Researchers often use two-way mirrors to unobtrusively observe the
interactions of animals or children. For best viewing they must be in a
darkened room looking toward a brightly lit room. Because the subjects
are in a brightly lit room, when they look in the mirror almost all of
the light that reaches their eyes is reflected back to them from the room
they are in and it looks like a normal mirror. Because the researchers
are in a dimly lit room, when they look in the mirror almost all of the
light that reaches their eyes is coming from the other (brightly lit)
room. If the lights in the researchers' room were turned up bright or if
the lights in the observation room were turned down low (or off) the
subjects might be able to see the researchers.
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Update: June 2012