# Blue afterimages are... blue?

**URL:** <https://boards.straightdope.com/t/blue-afterimages-are-blue/409557>\
**Category:** Factual Questions\
**Created:** [June 27, 2007, 12:37am UTC](https://boards.straightdope.com/t/blue-afterimages-are-blue/409557 "2007-06-27T00:37:48Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![HMS\_Irruncible](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hms_irruncible/32/7394_2.png) [@HMS\_Irruncible](https://boards.straightdope.com/u/HMS_Irruncible)\
**Post date:** [June 27, 2007, 12:37am UTC](https://boards.straightdope.com/t/blue-afterimages-are-blue/409557/1 "2007-06-27T00:37:48Z")

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While staring at some police-car flashers last week, I noted to my surprise that I saw afterimages that were exactly the same color of blue as the actual color of the flashing lights. I thought afterimages were supposed to be some complementary shade, not the exact same shade. This was when I stared at the lights for a few minutes and then closed my eyes. I made sure to check it several times.

What gives? Is it something special about the lights, or is it something special about me? If it helps any, I think the lights were the LED variety, which I think are monochromatic (or at least a very narrow band of) blue.

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**Author:** ![mangeorge](https://avatars.discourse-cdn.com/v4/letter/m/d78d45/32.png) [@mangeorge](https://boards.straightdope.com/u/mangeorge)\
**Post date:** [June 27, 2007, 12:47am UTC](https://boards.straightdope.com/t/blue-afterimages-are-blue/409557/2 "2007-06-27T00:47:52Z")

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Are you sure you weren’t looking at those lights through a, ahem, purple haze? 😛  
Seriously though, I just stared at my ceiling light (a CFL) then closed my eyes. The afterimage looked the same, I think. Then I turned on my L.E.D. flashlight and stared at it. Same thing. Now I need a colored light.  
Ah be bock.  
Peace,  
mangeorge

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**Author:** ![Terminus\_Est](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/terminus_est/32/3087_2.png) [@Terminus\_Est](https://boards.straightdope.com/u/Terminus_Est)\
**Post date:** [June 27, 2007, 1:16am UTC](https://boards.straightdope.com/t/blue-afterimages-are-blue/409557/3 "2007-06-27T01:16:45Z")

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There are two types of afterimages. A positive afterimage is caused by a bright light. This is what you saw looking at the police flashers. Negative afterimages, which is what you’re thinking of, is caused by fatiguing of the photoreceptors.

> **[Afterimage](https://en.wikipedia.org/wiki/Afterimage)**
>
> An afterimage is an image that continues to appear in the eyes after a period of exposure to the original image. An afterimage may be a normal phenomenon (physiological afterimage) or may be pathological (palinopsia). Illusory palinopsia may be a pathological exaggeration of physiological afterimages. Afterimages occur because photochemical activity in the retina continues even when the eyes are no longer experiencing the original stimulus.
> The remainder of this article refers to physiological a...