# I Light travels only in one direction material?

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1. Mar 9, 2017

### jms4

I would like to know if their are any materials that would allow light to pass in only one direction, In electricity we have diode, which will allow electricity to pass in only one direction, in optics how do we reflect light from one side and allow light from the other side to pass through?

2. Mar 9, 2017

### phinds

Ever hear of a one-way mirror?

3. Mar 9, 2017

### jbriggs444

A one-way mirror is one way only because the room on the back side is darkened. There is no asymmetry in the ability of a partially silvered mirror to pass light in one direction or the other.

4. Mar 9, 2017

### phinds

Oh. I knew it was much more effective if the one room was much darker but I thought there was SOME asymmetry. Wrong again, huh? Well, thanks for the correction.

5. Mar 9, 2017

### rootone

It depends what you mean by 'direction'.
It's easy to make filters that 'polarize' light, they are often used in cameras and sunglasses,
It cuts down on a thing known as 'glare', spots of intense light are reduced, so the received image as a whole has less contrasts

6. Mar 9, 2017

### physmath

Optic isolator, widely used in fiber optic systems, is a directional device made based on polarizing and rotating light polarization. If there's material with polarizing surfaces, its proper bulk might be the material you are asking?

7. Mar 10, 2017

### sophiecentaur

I have a suspicion that you couldn't make a domestic mirror that way because it would only work on axis.

8. Mar 10, 2017

### Khashishi

To be clear, the optical isolator based on Faraday rotation will absorb light going in the "wrong" direction, not reflect it. It gets absorbed in the polarizers. If you could reflect the light in one direction only, you would have a Maxwell's demon.

9. Mar 10, 2017

### sophiecentaur

There is a microwave equivalent to the optometrist isolator and that is the Circulator and Isolator - which again dump power from one direction into a load.

10. Mar 11, 2017

### jms4

Thank you all for your replies,
First, let me tell the whole thing,
1. I need a material which would allow light to only pass in one direction
2. In one side it would allow the light to pass through
3. In the other side, it should reflect the light back, not absorb it,

One way mirror is a semi reflecting mirror which allows 50% of the light to pass through and allows the other 50% to reflect back, I need something like at-least 90-10%, which allows 90% to pass through and reflects 10% back, ideal(100%) is not possible, so something like around 80-90% would be fine.

11. Mar 12, 2017

### Khashishi

You want the impossible. Do you see how a true one way mirror could be used to build a perpetual motion machine?

12. Mar 12, 2017

### sophiecentaur

Actually, it's not like that in practice. A 'One way mirror' that you see in use consists of a pattern (strips, usually) of normal mirror with alternate gaps. The way it works relies on the fact that the (observation) room, behind is kept dark so that all the 'observed' can see is the bright reflections. There is no reflecting surface on the observer's side so they just see the light admitted through the gaps. The ratio of thicknesses of mirror strips to gaps can be what you want. If you choose 10% 90% ratio then you will get 10% back and it will pass 90%. But 90% of the light from behind the screen will get through in the other direction, through the holes. Nothing more is possible, as Khashishi has said.

13. Mar 12, 2017

### tech99

I think a circular polariser will do this, if located above a mirror. This is because the reflected light is opposite-hand polarisation and is reflected from the polariser.

14. Mar 12, 2017

### ZapperZ

Staff Emeritus
15. Mar 13, 2017

### sophiecentaur

From your description, there seems to be a mirror in the way which would stop any light getting through in one direction (?).

16. Mar 14, 2017

Yes, agree.