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Author Topic: Why does looking at a bright light give you spots before your eyes?  (Read 95096 times)

Offline Chemistry4me

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I think I've been looking at the screen for too long. In addition with the light experiments, my well-being is even worse!
 

Offline Karen W.

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when i come from otside in the sun...My field of vision goe totally black....you know the song..."Blinded by the light" takes two to three minutes to adjust plus a huge heaache...

never seen colored spots..but white floaters when the blood pressure is two high....

Hope your head stops hurting right away....
you need a defuser screen on your monitor they help.....

Sorry for your headache...
 

Offline John Chapman

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Oh no. You're not going to sue me for damages, are you? I do like to see someone prepared to suffer for their science.

I've decided that in the absence of anyone confirming that I'm not a freak I'm just going to have to pluck my eyes out. If anybody reading this has experienced my freakish visual anomaly for themselves please speak up quickly as it will only take a few minutes for me to find a teaspoon!

In the meantime, sorry Chem4me about the headache!  ;D
 

Offline Chemistry4me

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In the meantime, sorry Chem4me about the headache!  ;D
No worries :) Plenty more clone eyeballs to spare experiments coming up!
 

Offline Chemistry4me

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Okay so one of my useless clones I went outside and had a look around, then I came back in and looked at a white wall... NOTHING! Not literally, just nothing colourful :)
 

Offline Chemistry4me

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Still NOTHING!
 

Offline John Chapman

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Ha ha. I think I'm definitely a freak.

I'll just have to wait and see if anyone else reading this thread has experienced the same. When I started it I assumed that everyone would instantly know what I was talking about. Thanks for getting all the Chem4mes having a go.
 

Offline Chemistry4me

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The weird thing is, I think I'm a freak as well (but a different kind)!
This morning, I did a 100m sprint and afterwards my vision was blurred and everything was really bright.

BEFORE.



AFTER




IT was freaking me out!!  :( :( :( :(
 

Offline Chemistry4me

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WHAT'S GOING ON?
 

Offline John Chapman

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Hi Chem

That would worry me. Are you a fit person? Has this happened before?

I would be tempted to check that out with my GP. Be careful. :)
 

Offline Christopher1

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What blot you are looking at...



newbielink:http://www.southcoastrecovery.com/ [nonactive]
 

Offline John Chapman

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Hi Christopher1.

Welcome to the site.

I am trying to establish whether other people experience colour changing blotches floating in their vision after looking at a bright light. The original question was:

Can anybody tell me why, after a bright light is shone into your eyes, you then see a dark purple blotch floating in front of your vision?

Also, if you blink or close your eyes at this stage the blob will instantly turn bright green while your eyes are closed and back to purple once they are open again. Why is that?

It seems that generally people experience the 'light blotch' but no-one here knows what I am talking about when I say it changes colour when I close my eyes. What do you think?
 

Offline yor_on

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John if I remember right it is the fluid or rather gel we have inside our eyes that make that effect. The reason we notice it is that the rods and cones that react to light sits on the 'bottom' of our eyes, so light have to traverse the full length of the eye before getting 'registered' by the brain. That gel have small 'impurities' in it that we don't notice normally, but can see at times.

And colour is just the way your brain might interpret a light stimuli. Or was it the Iris? Anyway, if you close your eyes and press on them with your fingers you will be able to see both shapes and colours, not because there is light coming to them, just because that pressure you are applying on your eyes will be interpreted by the brain as having both shape and colour.

"The rods are more numerous, some 120 million, and are more sensitive than the cones. However, they are not sensitive to color. The 6 to 7 million cones provide the eye's color sensitivity and they are much more concentrated in the central yellow spot known as the macula."
http://www.kellogg.umich.edu/patientcare/conditions/anatomy.html
« Last Edit: 16/02/2009 22:29:19 by yor_on »
 

Offline yor_on

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Mr Chem, as you run your blood pressure goes up, as your heart and lungs works 'overtime' to keep you oxygenated. In fact, your body behaves much the same as when under threat.

"When under stress your body prepares to deal with the situation. Several hormones are secreted from your adrenal glands to allow your heart rate to speed up, to constrict the blood vessels to your gut and to enlarge the blood vessels to your muscles, to dilate your eyes so you can see better. 

Those hormones stimulate your liver to release glucose for quick energy. Fat deposits are induced to liberate free fatty acids for fuel. 
our body does this so you are in a heightened state to deal with the event that is causing your stress. "

Mr Chem?
Does this mean that you see glades as a threat to our security?
 

Offline techmind

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Can anybody tell me why, after a bright light is shone into your eyes, you then see a dark purple blotch floating in front of your vision for several minutes?

Also, if you blink or close your eyes at this stage the blob will instantly turn bright green while your eyes are closed and back to purple once they are open again. Why is that?

The bright light momentarily bleaches the photo-receptors in the retina of the eye. The effect is typically noticed for up to a few minutes for 'common' bright lights, but may last longer if the light is seriously/dangerously bright.

The after-image colour you see is often substantially complementary to the colour of the bright light, so a bright red light might tend to create a cyan after-image, and a blue light might make a predominantly yellow after-image - if you're looking at a white surface. It does depend what colour (and brightness) surface you're looking at.

If you see the after-image when looking at a white surface then you are effectively subtracting a portion of the colour from the previous exposure... but if you shut/cover your eye so no 'new' light is entering, but still see an after-image then clearly there must be a different effect at work.


Having just done some empirical study :), I notice that the coloured splodge I see with my eyes open (against a bright surface) is slightly dark, while if I close my eye I see a bright burn-in on a dark backgroud (mysteriously my brain makes it come and go).

Having used a bluey-LED cycle lamp, I'm seeing a yellowy blob against the white on my computer-screen, but a magenta-y blob against the cream-coloured wall. When I close my eye and make it dark, I see a cyan coloured blob. But the colours change as the burn-in weakens.

I reckon that as well as the physcial bleaching, the brain plays tricks to conceal the physical artifact (which partly explains why the blob comes and goes), and this may also cause the colour to change.


Another thing you may observe is that if you've been laying in the sun for a few minutes with your eyes shut (you'll see the bright red of the blood in the eyelinds), when you open your eyes and look around everything will look bluey-green (and completely lacking in red) for a few minutes until the red-receptors have recovered.  [8D]
« Last Edit: 16/02/2009 18:54:57 by techmind »
 

Offline John Chapman

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Hi yor_on

Are you suggesting that the reason looking at a bright light creates a blotch is because it illuminates blobs of 'stuff' floating within the vitreous humour that aren't normally visible? Why would we still be able to see them after the eyes are closed? I think what you are describing is a different phenomenon to the one I mean. Are you talking about what I think are known as floaters? I don't know why you see light when you squeeze your eyeballs but I always guessed that this increases the pressure within which somehow triggers the rods. I've often also wondered why you see flashes of light when you bang your head or even stand up too quickly. I may post this as a separate question.


Hi Techmind

That's a really good answer. So that's you, me and Chem4me who have given ourselves migraines peering into our torches. Do you think we could all sue Chris Smith if we go blind by experimenting for his site!!! (only joking, Chris)

What you said about laying in the sun was interesting:

... if you've been laying in the sun for a few minutes with your eyes shut (you'll see the bright red of the blood in the eyelids), when you open your eyes and look around everything will look bluey-green (and completely lacking in red) for a few minutes until the red-receptors have recovered.

So that's sensory adaptation at work.

But what really interested me was your explanation for the colour change. I assumed the significance of having your eyes open or closed was the light or dark environment within the eye. But your experimentation suggests that it is caused by mixing the colour of the blotch with different background colours, the colour of 'eyes closed' being either red or black depending on ambient light conditions. That's excellent.
« Last Edit: 16/02/2009 19:47:08 by John Chapman »
 

Offline Make it Lady

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I think your colour detecting cone cells are recovering from the exposure to bright white light at different rates. Because white light stimulates all your colour detecting cells they stop sending signals to your brain. As some of them recover your spots will take on colours.

You are not a freak.

Try this spooky experiment but don't tell Paul as he will transfere it to kitchen science.

Colour Change Casper
If your Halloween party is becoming rowdy try this eye tricking experiment. Children have to concentrate on a picture of a ghost. This usually quietens them down as concentration requires quiet!
 
What you need:
   Some sheets of blank white paper (A4 is fine)
   A thick red and a thick black felt tip
   A bright light (sunlight or a table lamp)

What to do:
1.   Draw the outline of a ghost (about 8cm high) on the left hand side of a blank piece of white paper.
2.   Colour in the ghost with the red felt tip.
3.   Hold the paper with the ghost on it at arms length.
4.   Make sure a bright light is shining on the paper either by standing close to a window or by pointing a lamp at the page.
5.   Stare hard at the ghost for about 30 seconds. Stare at the same place in the centre of the ghost. If you need to blink do it quickly.
6.   After the 30 seconds are up, blink your eyes quickly once and then stare at the right hand side of the paper. This area should be blank but you may see something strange.
TIP: You should see a green ghostly image but if you donít try blinking a few times and staring at white paper again. If this still doesnít work repeat the experiment again with a brighter light shining on the paper.

I exSPECTRE want to know whatís happening:
The reason why you see a different coloured image after staring hard at a coloured ghost is that you have tired out the light receptor cell at the back of your eyes. Coloured light detector cells are called cones and no you canít eat ice-cream out of them! There are three types of cones. Each type detect either red, green or blue light allowing you to see all possible colours by colour mixing. White light is made by combining red, green and blue light so all cones are stimulated when you see white light. If you stare at a red ghost your red cones will get tired and the longer you look at red the less signals the red cones send on to your brain. When you change and stare at the white paper the green and blue cones tell the brain that they are being stimulated but the red cones are too tired to send any more messages for the ghostís position on the eye. You should now see a blue/green ghost floating on white paper as only the blue and green cones are sending messages to the brain where the ghost was positioned. Repeat the experiment with a black ghost.

 

Offline yor_on

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Hmm, maybe you're right John:)

But I have a memory of them becoming more visible when looking at bright spots.

John I didn't say that you would see 'floaters' when pressing on your eyes.
I said that that colours and shapes you will see then is a way of your brain interpreting electrochemical stimuli coming from your optic nerve due to the pressure placed on those eyeballs by your fingers.
 
I will split my first comment in two so that one can see that I was talking about two things more easy.

I also have a vauge memory that if you close your eyes with a bright light shining on them you will also be able to see those 'floaters'

http://www.triadpublishing.com/eyecarereports/floaters.shtml
« Last Edit: 16/02/2009 22:46:52 by yor_on »
 

Offline John Chapman

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Thanks for that, yor_on. And that link was very interesting.

Sorry about the confusion with your previous post. Your comments were clearly and intelligently put. It was my response that was misleading.

Yes, I realised you weren't suggesting that floaters are made visible when your eyes are closed or by applying pressure. I was pointing out, though, that my blotches are. Which is why I said that I thought that my blotches are the result of a different phenomenon to yours. Because I referred to all your comments using a single paragraph I seemed like I was mixing them up.
 

Offline John Chapman

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Hi Make it Lady

That's fantastic! I thought we had this licked with Techmind's answer. But it really seems like you might have hit the nail on the head. And very entertaining too.

At the stage where you look at the blank paper and see the blue/green floating ghost, what happens if you close your eyes and cover them so they are in darkness. Do your eyes continue to generate an image? And if so what colour is it?

I'd like to hear your answer but I'll try it myself as well.
 

Offline Chemistry4me

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Mr Chem?
Does this mean that you see glades as a threat to our security?
Eh? I don't know what you mean ??????

-----
Thanks for the reply Mr.yor_on :)
 

Offline Chemistry4me

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Hi Chem

That would worry me. Are you a fit person? Has this happened before?

I would be tempted to check that out with my GP. Be careful. :)
It has happened once, at exactly the same event: the 100 m sprint! All the other running is fine but I must not have warmed up properly or I am simply just not used to the explosive nature of the 100m!
 

Offline Make it Lady

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I quite often get a rush of blood to my head after sprinting (not that I do it any more, far too creaky.) You must remember that you do have blood vessels feeding your eyes so sudden changes in blood pressure can change your vission.

 John I've not tried out what you said about shutting your eyes. I will let you have a go as I have been doing eggciting eggsperiments al day with 5 to 11 year olds. I'm bloody knackered.
 

Offline yor_on

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Mr Chem?
Does this mean that you see glades as a threat to our security?
Eh? I don't know what you mean ??????

Well Sir, there are some associating open places with danger, and as we already established the connection is there (exhaustion/danger)...
It all depends of course, in a serious 'situation' that feeling might be shared amongst all involved I would say?
It can't help but start me wondering again, though?

You wouldn't, by any chance, enjoy a nice swim and boating now and again?
Ah, like those fellows? http://www.specialboatservice.co.uk/
Sounds like they're giving a really good service, although I couldn't for the world find out about their fares?
(Awh, it just sort of 'popped up':)
« Last Edit: 17/02/2009 18:16:17 by yor_on »
 

Offline Make it Lady

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Are you on drugs?
 

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