I am thinking of ways of achieving parallel rays of light.
Let's say I have an object that emits light, for instance the display of my mobile phone. The display emits rays of light in every direction.
Is there a "filter" I can put in front of the screen that only lets rays of light traveling in a certain direction through – e.g. only rays of light traveling orthogonal to the screen?
Or what other ways are there to achieve parallel rays of light?
Best Answer
The commonly available 'privacy screen' does this by blocking light beyond a certain angle off perpendicular. Typically the narrower the cutoff angle, the more expensive, but these work well for privacy.
They don't actually collimate light into an absolutely parallel beam, but in reality you wouldn't want this, as it would make the device quite unusable (you would only see a small area of the screen at any time), so what they actually do is allow between 15 and 30 degrees either side of 90 degrees, and heavily attenuate any light outside these angles.