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Simple question, I've always wanted to know the answer to this.

Why do you see a pair of lines radiating out from street lights when your squint at them? I can't think of a better way of describing what I mean, but I hope one know what I'm talking about.

Is it some sort of diffraction effect causes by your eyelashes acting as a grating?

Any ideas would be greatly appreciated :-)

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Diffraction seems plausible. boards.straightdope.com/sdmb/showthread.php?t=630308 - This random discussion forum brings up another possibility: The eyelids distort the shape of the liquid on the surface of the eye, causing bad lensing in the vertical direction. That one seems plausible too. I don't know which (if either) is correct. –  Steve B Aug 15 '12 at 13:41
    
I'm not sure everybody sees what you see. After I had Lasik surgery, I saw an irregular polygon with wiggly sides around each point source light. I attributed this to my pupil being open wider than the corrected part of my lens: so the inner part of my lens was correct and focused light to point and outside part of my lens was uncorrected by lasik and focussed light to a blur and I saw these overlapping. –  mwengler Aug 15 '12 at 19:01
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1 Answer

This is apparently a diffraction pattern due to eyelashes and perhaps even eyelids; closely related to "lens flare", "diffraction spikes" or "aperture stars".

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