How It Works
A one way mirror works, by combining the functions of a window, and a common window advertisement. Below is an explanation, as to how a one way mirror posses it's half reflective/half transparent properties
Diagram Explanation
- Incident Ray: the ray of light that shines onto a surface
- Normal: an imaginary line that extends 90 degrees from the base, running between the incident ray and reflected ray
- Reflected Ray: the ray of light after it bounces off a surface
- Base: Surface in which the light rays reflect off of
Standard Mirrors
- In a standard mirror, the surface is a very smooth and flat
- Following the laws of reflection, when parallel incident rays head towards the mirror they all hit the mirror and stay parallel after becoming reflected rays
- Rays staying parallel is because the reflective surface is very smooth, allowing each of the rays to hit the surface at the same angle, therefore all reflecting off at the same angle too
- This results in specular reflection, which is why you can see a perfectly reflected version of yourself when you look into a mirror
- In a window ad, the surfaces are not very flat (diagram exaggerated to show different angles of reflection)
- When color reflects back, it reflects at different angles since it hits the surface at different angles (shown with the black and brown line). This results in diffused reflection, which is why it doesn't look like a (colored) mirror
- In the sheet, ~50% of it is covered in ~3mm holes, which allow light through
- Usually, the non-image side is facing a (relatively) dark place, like the inside of a bus or shop, while the image side is in the bright daylight
- From the image end (also the bright end), most of what the viewer sees is the image (light coming through holes are dim, light reflecting off image is vibrant and bright), therefore you see an picture instead of through the sheet
- From the non-image end (also the dark end), most of what the viewer sees is the window (light coming through holes are bright, light reflecting off of black covering is dull and dim), therefore you see mainly a window instead of a black covering
One Way Mirrors (How It Works)
- Combines concepts of both mirrors, and window advertisements
- Has small microscopic gaps in the reflective coating that accounts for 50% of the mirror, much like the window advertisement
- 50% of the light hits the mirror part, and is reflected back as a specular reflection because of the smoothness of the mirror
- Other 50% of the light passes though the microscopic holes in the mirror, therefore being transparent in 50% of the mirror
- This means 50% of the light is allowed through the one way mirror, while the other 50% is reflected back
- Both sides of the mirror function the same
What Makes It One Way
- From what was learned before, 50% of what you see is reflection, other 50% is window
- What makes it one way, is when one person stands in a dark room on one side, while the second person stands on a bright side
By having one side of a one way mirror exposed to light while the other side into the dark, the dark side sees a window while the light side sees a mirror:
Dark side:
Light Side
All this results in the dark side seeing a tinted window, while the light side sees a slightly less reflective than usual mirror.
Dark side:
- 50% mirror side shows reflection, but it reflects nothing because there is no light emitting from the dark side
- 50% of the mirror shows window, which has tons of light streaming in from the light side
- Only the window half of the one way mirror shows light, therefore it acts as a window
Light Side
- 50% mirror side shows reflection, which shows up well because the light side has an ample light source to reflect
- 50% of the mirror shows window, which shows nothing because there isn't light in the dark side to be released
- Only the mirror half of the one way mirror shows light, therefore it acts as a mirror
All this results in the dark side seeing a tinted window, while the light side sees a slightly less reflective than usual mirror.