Why does a polarising filter cut off the life from a computer monitor?

rgrebby

rgrebby

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Richard
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erm, I meant light...

When turned at the right angle it cuts out all the light coming from a computer monitor.
Turn is a little more and you can see fine.

How come?
 
As its supposed to cut down the glare from the sun, I assume it does the same for the light coming from the monitor as well :shrug:
 
Because the light from the monitor is polarised, putting another polariser in front of the monitor will as you have found out cut the light out completely :)
 
Your monitor has a polarising filter on it to reduce glare, much as a pair of poloroid sunglasses does. The filter on the monitor will polorise the light into one plane (for sake of arguement say upright) if you look at the screen through your camera filter and the two planes are equal you will see light, as you turn the camera filter you will change the plane and the light will reduce, when you get to 90 degrees to the monitor filter no light will get through and the monitor will look like it is off.

You can use this in photography, you can fit polorising filters to your light source ( say studio flash lights) and fit a polorising filter to your camera, by changing the orientation of the filter on the camera you can get some different effects, if you do this technique and light some clear plastic you will get rainbow type stress pattern, this is called birefringence!
 
Erm....must be polarised ;) Just tried this with my filter and it's pretty cool, looks like the screen is off while all the stuff around it is fine. Only works if i look through from the front of the filter otherwise it appears to cool or warm the scene.
 
Cir pola is faced and therfor will only work correctly one way round.
Lin ploa is not so it will not be affected by each face.
Not entirely sure monitor are polarised, some may have a 1/4 wave retarder in front of the screen but im not certain, I think it may be to do with the way lcd's emit light.
Dean:)
 
EdBray said:
You can use this in photography, you can fit polorising filters to your light source ( say studio flash lights) and fit a polorising filter to your camera, by changing the orientation of the filter on the camera you can get some different effects, if you do this technique and light some clear plastic you will get rainbow type stress pattern, this is called birefringence!
Click to expand...

Another application for this technique:

I had to photograph a huge oil painting, with big lumps of dark paint sticking up. No matter what I did with the lights, the painting was covered in little bright stars. I put polarising sheets 1ft square over both lights, and a filter over the lens rotated 90degs. The reflections disappeared :)
 
EdBray said:
You can use this in photography, you can fit polorising filters to your light source ( say studio flash lights) and fit a polorising filter to your camera, by changing the orientation of the filter on the camera you can get some different effects, if you do this technique and light some clear plastic you will get rainbow type stress pattern, this is called birefringence!
Click to expand...

I remember this from doing photoelasticity at uni, counting all the damn fringes of a plastic component in the polariscope to work out the stresses :bonk:
 
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