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?