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The eyes and dark conditions.

  1. Apr 20, 2005 #1
    I have had a few people say, turn on a light when your on the computer, or your going to ruin your eyes.

    I have spent the last 10 years behind a computer screen never with a light on. My eyes are perfectly fine. When I went for drivers license i for 20/20 and the smallest font size was completely visible. I bet i would be able to see half that size.

    So my question is. Is that correct scientifically? The only light i have when im on the computer is the light that is caused by the monitor.
     
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  3. Apr 20, 2005 #2

    cronxeh

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    dont listen to those people.

    its been 12 years for me - from 4 colored CGA screens to VGA to SVGA to XGA to modern day standards on 19" screens to finally a laptop - and I always used them in the dark, and never had my vision deteriorate. Its simple physics really. Less radiation entering your eye, less irritation on the iris. Now the focusing muscles might weakened, but so far it never happened - keep a decent 1.5-2 feet distance from your screen and you'll be alright
     
  4. Apr 20, 2005 #3

    Moonbear

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    It's more of an issue of eye strain, or fatigue of the eye muscles. If it doesn't bother you, then don't worry about it. But, if you start getting headaches or have some trouble focusing after working on the computer a long time, remember to stop and let your eyes rest once in a while or focus on something further away. That's really what having the lights on helps with is making sure the rest of the room around you is bright enough to so you look up once in a while and focus on something else.
     
  5. Apr 21, 2005 #4

    Ouabache

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    Speaking of "eyes in dark conditions"

    I was down at our observatory the other day, looking at some galaxies, nebulae, and clusters of faint stars. The lead astronomer told everyone to allow their eyes to become dark adapted as they are considerably more sensitive to subtle light variations when totally dilated and equalized to the dark surroundings. Then he asked us all to use averted vision to better be able to observe deep sky objects. I didn't have a clue what he was referring to.

    He went on to explain some fascinating things about our eyes. If you normally peer into a telescope with your right eye, there is a blind spot located to the right hand side of direct center, so concentrating vision slightly to the left will increase your ability to see finer detail and color. It is symmetrically opposite for the left eye. He pointed out that the very center of your eye is called the yellow spot and contains only slightly sensitive cones.

    For averted vision, he wanted us to look further to the left (for the right eye) so that we may use more of the light sensitive rods. Evidently there are some 120 million rods per eye and only 7 million cones. On top of that, the rods are 10,000X more sensitive to light than the cones. So it was best looking out of the corner of the eye, to observe planets, faint stars and faint deep sky objects. And to strengthen our vision more, eat plenty of carrots (Vit A). :smile:
     
  6. Apr 21, 2005 #5

    DocToxyn

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    I think the "yellow spot" he was referring to is called the fovea. It is indeed packed with the more color-sensitive cones and if you are trying to see images in low light it is better to "look sideways" as this moves the focus away from the fovea and onto the more light-sensitive rods. I have noticed this many times at night as this is the only time I have to run and dark-adapted vision is critical :bugeye: . Supposedly it is also an advantage to be colorblind since the lack of certain cones permits better rod function.
     
  7. Apr 21, 2005 #6

    selfAdjoint

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    This sideways trick also works when you are trying to see an extremely low contrast object in brightness, like seeing Venus in the daytime sky.
     
  8. Apr 21, 2005 #7

    Moonbear

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    I've never heard anyone refer to the fovea as the "yellow spot" before either, but I'd have to concur that would be the best guess.
     
  9. Apr 22, 2005 #8
    The idea is that when one looks at a lit screen in the dark, there is more radiation, not less, because the eyes are more dark adapted then they would be in a lit room.
     
  10. Apr 22, 2005 #9

    cronxeh

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    it is less in a sense that there are less photons per second entering your retina

    i dont know where the notion of 'dark adapted' came from, but im willing to speculate its a psychological mode of the brain to 'recognize' the low area density of photons as compared to being a physiological thing
     
  11. Apr 22, 2005 #10

    selfAdjoint

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  12. Apr 22, 2005 #11
    I've done quite a bit of star gazing, and it is definitely important to let your eyes adapt. In fact, astronomers claim it takes 45 minutes to let your eyes fully adjust. If you are going to look at a star chart, it is recommended that you put a red filter over your flashlight, as that will allow your pupils to remain dilated and you won't need to wait another 45 minutes to "reset" your night vision.

    Here's a question, though - does anyone know how the production of melatonin in the body is related to pupil dilation? From what I know, in a natural setting, as dusk begins, so does the body's production of melatonin. What triggers this production? Meaning, how does the body know it is dark? Does pupil dilation have anything to do with it? If you have been under a dark sky for a while and then use a red light to read for an hour, would your body continue to produce melatonin, thinking it is dark?

    These questions may seem really random. Really, I'm just curious as to whether or not the use of red lights in households in the hours before bedtime--as opposed to bright white light--can help reduce the risk of cancer. When it gets dark, the body produces melatonin (which has been shown to be a cancer-killing hormone). So if you fool the body into thinking it is dark, will the body go ahead and begin melatonin production?

    That's a really, really brief way of explaining what I'm looking into, but I hope you understand. If you want me to elaborate, or give a few links to studies, I can.

    Finally, here's one statistic that just made me sigh:
    Average hours a night people slept before Thomas Edison invented the light bulb: 10
    Average hours a night people sleep today: 6.9
     
  13. Apr 22, 2005 #12

    DocToxyn

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    It's not related to pupil dilation directly, rather both reactions, dilation and melatonin synthesis, occur due to reductions in light input to the eyes. The connections from the eye to the brain responsible for conveying ambient light status begin with structures in the hypothalamus descending to the spinal cord and then back to the pineal gland, sometimes referred to as the third eye, due to its reaction to light cycle. The pineal then synthesizes melatonin for circulation througout the body. The red light should not significantly disrupt melatonin production, most circadian rhythm researchers use red lights when they have to work with animals that are in the dark phase of the light cycle.

    It's an interesting concept and not one that isn't receiving current scientific investigation. It may not require such extremes as using all red lights in your house at night, but it could be a potentially easy way to reduce certain risk factors for certain cancers. However, I would submit that the research is still underway and fooling around with your circadian clock without knowing exactly what parameters to change could have other, potentially negative effects.
     
  14. Apr 22, 2005 #13

    Moonbear

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    Not just red light, but DIM red light. < 3 lux, and you have to be sure not to directly shine it into an animal's eye. I've worked under those conditions for years. It is just barely enough light to see what you're doing so you can find the animal you're looking for (to work under those conditions, you have to have double doors like a darkroom to enter, so no light from outside ever enters the room). It only takes me a few minutes to adapt to the darkness (though I swear a lot when someone leaves a broom in the wrong place; for the first few minutes in a room like that, you really can't see anything, so you have to keep things in very specific locations so you don't trip over anything until you adjust). The bigger shock is the first minute after stepping back out into the lit corridors. :bugeye: It's much easier to take the night shift on those experiments because I can usually get away with shutting off all the corridor lighting except the emergency lighting that has to stay on, so I don't get blinded when stepping back into a brightly lit hallway.

    My house is more brightly lit than that just from street lights and all the lcd lights on digital clocks, phones, laptop power cords, etc. I actually have a cordless phone I have to take out of the charger at night because the LCD is bright enough to keep me awake. I function better than most in the dark though. Even when we have a blackout, as long as the next block over, on a different power grid, still has street lights on, there's enough light for me to find my way around my house without flashlights or candles.

    Our local zoo has actually had problems breeding some of their animals from the exposure to neighborhood lights in the winter (this is the challenge of having a zoo in a city). They had to move animals into special enclosures to keep the lighting better controlled. I wouldn't be surprised to find there are higher incidences of sleep disorders in cities than in rural areas.
     
  15. Apr 22, 2005 #14
    Thank you for the link. I hadn't seen that article yet, and it is quite helpful.

    Agreed! However, I don't think using red and/or dim lighting after dusk would be harmful, since it seems, well, "natural." I would think being in bright lights after dark certainly messes with circadian rhythyms more than red lights would.
     
  16. Apr 23, 2005 #15
    The retina is at the back of the eye. The pupil is at the front. When a pupil dilates, it allows more photons to enter the front of the eye and hit the retina at the back of the eye.
     
    Last edited: Apr 23, 2005
  17. Apr 23, 2005 #16

    Moonbear

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    That would only be momentary. As soon as you look at the lit screen, your pupils will begin to constrict and adjust to the brighter light.
     
  18. Apr 24, 2005 #17
    Overall, the light is not bright, Moonbear. It is relatively bright in a small portion of your field of view (FOV) and relatively dark in the rest of your FOV. Therefore, since the light is not overall brighter, your eyes cannot adjust to brighter light. For as long as you look at a lit screen in a dark room, you have dark-adjusted eyes letting in too much light in a small portion of your FOV.
     
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