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Thread: Light trails (not photography related)

  1. #1 Light trails (not photography related) 
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    So I was sitting here playing with my laser pointer and watching the trail left behind as I move it quickly got me thinking. I spent some time trying to find an answer but all I could find was information about photographing light trails (from cars, stars, etc).

    Basically why is there a trail left when I move the pointer quickly? The beam is traveling at the speed of light, right? I understand that as I move the source of the beam, the beam that was emitted from it still has to reach the object it is pointed at so there would be a slight delay in changing the end dots location, however due to the speed of light being so fast it would effectively be unnoticeable.

    So when I flip the pointer back and forth really fast and get a nice multiple feet long trail of light, what is causing it? Is it simply the delay it takes for the light to reach my eyes, the reactions in my retinal cells to occur, send the information to my brain and my brain to process it?

    I'll end it here before I start rambling. I just hope you folks understand what I am talking about and can help.


    Always minimize the variables.

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  3. #2  
    Forum Radioactive Isotope MagiMaster's Avatar
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    The trail is an optical illusion. http://en.wikipedia.org/wiki/Afterimage


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  4. #3  
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    See that was simple enough that now I feel like an idiot for asking. Thanks though, it was really bugging me.
    Always minimize the variables.

    Semper Paratus
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  5. #4  
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    You say that the light trail is due to an after image? I dont think that thats the full correct answer. My eyes dont feel fatigued when I watch a laser pointer that has light trails. I also have a replica light saber that has the same exact light trials. My eyes definitely dont turn the red trails into complimentary colors like after images. My eyes feel fatigued when I stare at a color for 20 seconds and then see an after image from it. Light trails you see instantaneous. What I think a light trail is, is more so reflection and refraction from wave. I'm stumped!
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  6. #5  
    Forum Radioactive Isotope MagiMaster's Avatar
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    (This thread is several months old BTW)

    Wrong meaning of the word fatigue here. The individual rods and cones can be fatigued without you actually feeling it.

    Regardless of the exact details, it's definitely a property of the eye and not a property of the light itself. You can read a lot more here: http://en.wikipedia.org/wiki/Persistence_of_vision and in the related links.
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