Why do LCD TVs show color spectrum when light shines on them?

[Jimmy87]

Hi pf, I just noticed that when light shines onto my tv screen (when it is off) you see thin bands of colors reflecting back (see picture attached). I just wondered why this was and also why it ONLY happens if DIRECT light (from a bulb or the sun) hits it. Also, you only ever seem to get 4 lines?

Thanks.

 

[Drakkith]

I'd guess that the pixels are causing light to reflect and form an interference pattern. Different color light has different wavelengths, so the pattern is slightly different for each color, hence the reason the light is split into colored bands.

 

[sophiecentaur]

The four lines (two crossed lines) you see is because of the regular pattern on the screen. It is the same phenomenon as you get with a photographic starburst filter See this link for some pictures (rather than an actual explanation of the details of how a starburst filter works)
This link is a bit skimpy but tells you how the effect is due to spatial filtering - by passing light (or reflecting it from) regular patterns.

You can get starburst effects from the smears made by windscreen wipers and also when looking through fabric at points of light (look at a distant street lamp through the nylon fabric of black umbrella at night for a similar effect). And, of course, CDs can give the same sort of effect.