# Why do I see a light flash when startled in my sleep?

**URL:** <https://boards.straightdope.com/t/why-do-i-see-a-light-flash-when-startled-in-my-sleep/494064>\
**Category:** Factual Questions\
**Created:** [April 23, 2009, 5:05am UTC](https://boards.straightdope.com/t/why-do-i-see-a-light-flash-when-startled-in-my-sleep/494064 "2009-04-23T05:05:58Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![staciemic](https://avatars.discourse-cdn.com/v4/letter/s/fbc32d/32.png) [@staciemic](https://boards.straightdope.com/u/staciemic)\
**Post date:** [April 23, 2009, 5:05am UTC](https://boards.straightdope.com/t/why-do-i-see-a-light-flash-when-startled-in-my-sleep/494064/1 "2009-04-23T05:05:58Z")

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Sometimes when I’m almost asleep and wake up by a sudden loud noise I see a light flash. The more startling sound whiter and brighter the light is. Sometimes I see different colors with different noises and it only happens when I’m trying to fall asleep.

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**Author:** ![Der\_Trihs](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/der_trihs/32/233_2.png) [@Der\_Trihs](https://boards.straightdope.com/u/Der_Trihs)\
**Post date:** [April 23, 2009, 5:50am UTC](https://boards.straightdope.com/t/why-do-i-see-a-light-flash-when-startled-in-my-sleep/494064/2 "2009-04-23T05:50:57Z")

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Cecil speaks on a related issue; [Why do I see sparks when I cough with my eyes closed?](http://www.straightdope.com/columns/read/86/why-do-i-see-sparks-when-i-cough-with-my-eyes-closed)

My guess is the same principle is involved; you are startled, that produces a surge in blood pressure, that stimulates photoreceptor cells in the eyes.