Posted on 05 December 2011 at 12:16h

It's sad but true that the other night I was sat watching the blank screen on our flat screen LCD TV. What I noticed was that light reflected off the blank screen was being diffracted so  took a photo of it.

I was interested to know what was causing this affect, my guess was that the pixels were diffracting the light but were they small enough to cause such an apparently large angle of diffraction. To find out I took some rough measurements.

I was sitting about 3m from the TV and with my arm outstretched measured that the first two maxima to be 2cm apart. So diffracting angle for 1st order = 0.01/3.

For a diffraction grating dsinθ = mλ where m is the order (1)

Taking λ = 600nm gives a value of 0.18mm which is about the size of a pixel.

The second problem was the angle between the two diffraction patterns. Rows of horizontal pixels would give horizontal and vertical patterns. So, in true Sherlock Holmes style I magnified the screen with my magnifying glass. This is what I saw

Elementary my dear Watson.