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Message 1
From: "kitmengleong" kmleong@act.com.sg
Date: Sun May 7, 2006 11:57pm(PDT)
Subject: How to See in the Dark
How to See in the Dark
http://www.wikihow.com/See-in-the-Dark
Human beings cannot see in total darkness and in general, they do not
have very good night vision. However, it is possible to improve your
ability to see in the dark.
Steps
1. Take advantage of the structure of your eyes. The human eye has
'rod' cells and 'cone' cells on the retina, which is the sensory layer
at the back of the eye. Rod cells and cone cells are distributed
evenly throughout the retina except for the fovea, which is a small
area on the back of the eye directly opposite the pupil. At the fovea,
there are only cone cells. This is an important thing to know because
the 'cone' cells are more proficient at color detection, whereas 'rod'
cells are better for low light and detecting movement. Therefore, when
trying to see in low light, try not to look directly at the places you
are trying to see. By using your peripheral vision you are using more
rod cells, which work much better in low light. This takes a great
deal of practice for most people.
2. Keep your eyes adjusted for the dark. If you're in a lighted
area and know you're going to be going into a dark area, close your
eyes tightly, or at least squint your eyelids before entering the dark
to give your eyes a chance to adjust. If you can't close both eyes,
close one or place a hand over one. This works well when driving into
tunnels. Once you're in, avoid looking directly at any light source,
no matter how dim you think it is. It takes longer to adjust back for
the dark than it did for your eyes to adjust for the light you just
looked at.
3. Practice. This can be as simple as shutting out the lights in a
room and closing all portals, allowing only the ambient light that
slips in under the door. One place to work at it is in the bathroom
while taking a shower. You've probably been showering in the same room
for years and can practically navigate it with your eyes shut. Most
bathrooms don't have a large amount of windows, so there's less light
coming in. Just be careful and take it slow. All it takes is one rug
in the wrong place and you could fall, hit your head on the edge of
the tub, and drown in an inch of water.
4. Scan, don't stare. If you look at something, or a place, in the
dark for too long, your eyes will become less sensitive to what little
light there is. If you scan your eyes back and forth over the area you
are looking at, you will be using different areas of "rods" as
described above, and you will be able to see details clearer.
5. Protect your night vision. If you do need to use a light, having
a coloured lens over the light will help preserve your night vision.
White light, containing all frequencies, from red all the way to blue,
will ruin your night vision the fastest. Red is favored when you need
to recover quickly, green or blue-green should be used for acuity.
Whatever light that is used, it's important to use as low intensity as
possible.
Tips
* Practice seeing things without looking directly at them.
* Prepare yourself for the darkness before entering it.
* Avoid looking directly at light sources while navigating in the
dark. Even if you aren't looking at them directly, light sources close
to your face will diminish night vision. For example, if you are
smoking you might realize that the red/orange glow in front of you
provides enough light to cause your pupils to contract, therefore
killing your vision. Similarly, you will not see much if you're
wearing a miner's helmet with a light or carrying a flashlight
(excluding the beam of light itself, of course).
* Special Forces use the technique of squeezing your eyes shut
tightly for ten seconds - once you are in the dark. While the
technique can seem effective, scientific studies have not proved it
works. Perhaps its a case where the brain and belief override normal
physical reactions.
* Different people have different levels of ability in night
vision. While these techniques can help you reach your full potential,
your full potential may not be as great as that of others.
* Look for shapes, not colors. In tall grass, look for horizontal
lines that stand out against the vertical grass. These will indicate
an obstacle/target.
* When moving around in the dark, it is safer to move slowly and
slide your feet, using your toes to sense obstacles in front of you.
You're most stable when you have both feet on the ground, and are less
likely to trip and sprain, or even worse, break something. Also, if
you put your arms out to feel where you're going, cross them at your
wrists and form a circle with your elbows out to the sides, thus
helping you to keep your balance while avoiding walking into a post,
tree trunk or edge of an open door.
Warnings
* Traipsing around in your home or outside the house can be very
dangerous. You should weigh the facts of being "cool" walking around
in pitch black against hurting yourself badly.
* There's an urban legend about carrots helping one to see in the
dark. This is actually traceable back to a misinformation campaign by
the British air ministry during World War II. While there are
theoretically some benefits from extremely high doses of beta-carotene
in preventing ocular degeneration, and those suffering from
nyctalopia, a Vitamin A deficiency, can find some relief in the
consumption of carrots, this does not apply to the average person.
* Be careful when practicing moving about in the dark. If you fall
and hurt yourself, don't panic! Take a few deep breaths and re-orient
yourself before checking the extent of your injury and finding a light
source.
How to See in the Dark
Not sure I agree with (3) as I think you can seriously hurt yourself in a bathroom with the lights off. Has anyone here "practice" in the dark before?
As for (4), the rods must work differently from CCD if staring at a photon source reduces the sensitivity! I always thought that scanning enables you to pick up faint objects better because our brain is good at picking up moving objects.
Overall, nice summary for dark adaption!
As for (4), the rods must work differently from CCD if staring at a photon source reduces the sensitivity! I always thought that scanning enables you to pick up faint objects better because our brain is good at picking up moving objects.
Overall, nice summary for dark adaption!
[80% Steve, 20% Alfred] ------- Probability of Clear Skies = (Age of newest equipment in days) / [(Number of observers) * (Total Aperture of all telescopes present in mm)]