Playing around with some purple light thing

saturday night, nothing much to do, and it was time for the physics blog. of course, the camera was in video mode by chance, but before I switched it to picture mode, my good friend Richard asked, "what's that?" Sure enough, there was a random purple line thing in the middle of the screen. And it just wouldn't go away.

Confused, I sent the following message to doc!, in hopes of enlightenment:


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So, I was about to use my camera to take a picture at Richard's house, but the camera was in video mode. When I hit the "record" button, I noticed a distinct purple line which cross-sectioned the view of the room, and it seemed to originate from a lamp. I moved around the camera a bit, and saw that if I rotated it enough, the purple line disappeared.

Could you point me in the right direction so I could blog about it?

thanks,
andrew
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and here was the response:

Interesting. It appears to be some kind of internal reflection in the lens of the camera caused by the high intensity of the light. I would guess that it as you move the camera up and down, the purple line will stay directly on the lamp. Does the line rotate as you rotate the camera? This is something like the star effects that cameras as sometimes designed to produce ... those are diffraction effects.
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as the video verifies, doc!'s hypothesis that the purple line would only disappear if the camera were moved side to side is correct. unfortunately, I failed to grasp very much understanding here. I googled 'star effect' and every single result seemed to be selling something.

For now, the phenomena is unresolved, both because I am stuck and because I have a lot to do tonight. I am annoyingly very confused, just like how I will be on tomorrow's physics test.