rushintuit
sage
Reged: 04/01/06
Posts: 257
Loc: Farpoint Observatory
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Ed,
How long does it take your eyes to fully dilate?
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Edited by EdZ (08/10/06 09:23 AM)
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EdZ
Professor EdZ
Reged: 02/15/02
Posts: 12341
Loc: Cumberland, R I , USA42N71.4W
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Quote:
How long does it take your eyes to fully dilate?
About 10 seconds. It's not pupil dilation that gives you night vision.
It takes about 2 hours for your rhodopsin (visual purple) to regenerate after you look at bright lights. Computer screen, TV, headlights, they all deplete rhodopsin in seconds. Spend a day at the beach without sunglasses and it will take about 2 days for the bleaching effect to go away.
edz
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Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
member#21
Edited by EdZ (08/10/06 09:24 AM)
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Mark9473
Carpal Tunnel
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Posts: 2614
Loc: 51°N 4°E
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Ed, that was a great report. Felt like being there. Thanks.
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Mark
Leica 8x20; Vixen 8x42; Swift 8.5x44, 10x50 and 20x80; TS 7x50; Orion 15x63
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rushintuit
sage
Reged: 04/01/06
Posts: 257
Loc: Farpoint Observatory
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Very, very interesting! I had no idea it took that long. Is the regeneration of visual purple fairly linear over the two hour period?
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Edited by EdZ (08/10/06 09:33 AM)
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rushintuit
sage
Reged: 04/01/06
Posts: 257
Loc: Farpoint Observatory
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"It takes about 2 hours for your rhodopsin (visual purple) to regenerate"
From Wikipedia, the free encyclopedia:
Rhodopsin, also known as visual purple, is expressed in vertebrate photoreceptor cells. It is a pigment of the retina that is responsible for both the formation of the photoreceptor cells and the first events in the perception of light. Rhodopsins belong to the class of G-protein coupled receptors. It is the chemical that allows night-vision, and is extremely sensitive to light. Exposed to white light, the pigment immediately bleaches, and it takes about 30 minutes to regenerate fully in humans.
http://en.wikipedia.org/wiki/Rhodopsin
The 30 minute regeneration scenario seems more in line with personal experience.
Attatched photo: A rhodopsin molecule (yellow) in the cell membrane (blue). Retinal is shown in orange.
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/// Stellarvue SV102ED /// Nikon 12x50 /// Fujinon 16x70 /// SkyTools 2 /// The Desktop Universe All Sky CCD Mosaic In Monochrome Mode ///
Edited by EdZ (08/10/06 09:25 AM)
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Littlegreenman
scholastic sledgehammer
Reged: 05/09/05
Posts: 972
Loc: Southern California
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Quote:
"It takes about 2 hours for your rhodopsin (visual purple) to regenerate"
From Wikipedia, the free encyclopedia:
Rhodopsin, also known as visual purple, is expressed in vertebrate photoreceptor cells. It is a pigment of the retina that is responsible for both the formation of the photoreceptor cells and the first events in the perception of light. Rhodopsins belong to the class of G-protein coupled receptors. It is the chemical that allows night-vision, and is extremely sensitive to light. Exposed to white light, the pigment immediately bleaches, and it takes about 30 minutes to regenerate fully in humans.
http://en.wikipedia.org/wiki/Rhodopsin
The 30 minute regeneration scenario seems more in line with personal experience.
Attatched photo: A rhodopsin molecule (yellow) in the cell membrane (blue). Retinal is shown in orange.
I've heard/read the 2 hour period before, but I don't know where. I do know it was in relation to astronomical viewing. It could be that for more common activities, 30 minutes is good enough, but for seeing faint fuzzies you need that extra 90 minutes. I do know that that longer I'm out in the dark it just gets better!
Edited by EdZ (08/10/06 09:25 AM)
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EdZ
Professor EdZ
Reged: 02/15/02
Posts: 12341
Loc: Cumberland, R I , USA42N71.4W
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Quote:
Is the regeneration of visual purple fairly linear over the two hour period?
I don't think so. But AFAIK, full dark adaptation takes about that long.
See the Links thru the Binocular Weblinks to
The Eye and Night Vision
from
National Aviation Reporting Center
on Anomalous Phenomena
http://www.narcap.org/TheEyeandNightVision.htm
The Eye and Night Vision
(This article has been adapted from the excellent USAF Special Report, AL-SR-1992-0002, "Night Vision Manual for the Flight Surgeon", written by Robert E. Miller II, Col, USAF, (RET) and Thomas J. Tredici, Col, USAF, (RET))
Quote:
The fully dark-adapted eye, in which photopigment regeneration is complete, restores retinal sensitivity to its maximal level. Rods and cones differ markedly, however, in their rate of dark adaptation. Cones attain maximum sensitivity in 5-7 minutes, while rods require 30-45 minutes or longer of absolute darkness to attain maximum sensitivity after exposure to bright light.
The cones have a faster rate of photochemical regeneration because they function in greater light than the rods. The cones, however, do not achieve the same level of sensitivity as the rods. The rods slowly adapt to dim illumination, but eventually achieve a much greater sensitivity than the cones. Depending on the preadaptation to light, dark adaptation is about 80% complete within 30 minutes, but it may take hours, or even days, to acquire total dark adaptation.
and
Daytime exposure to ordinary sunlight can produce temporary but cumulative aftereffects on dark adaptation and night vision. Both civilian and military studies have documented significantly diminished rod performance after prolonged sunlight exposure at, for example, the beach or ski slope. Two or three hours of bright sunlight exposure has been shown to delay the onset of rod dark adaptation by 10 minutes or more, and to decrease the final threshold, so that full night vision sensitivity could not be reached for hours. After 10 consecutive days of sunlight exposure, the losses in night vision were reported to cause a 50 % loss in visual acuity, visibility range, and contrast discrimination. Repeated daily exposures to sunlight prolong the time to reach normal scotopic sensitivity, so that eventually normal rod sensitivity may not be reached.
edz
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Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
member#21
Edited by EdZ (08/10/06 10:08 AM)
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rushintuit
sage
Reged: 04/01/06
Posts: 257
Loc: Farpoint Observatory
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Edz,
From a practical standpoint, folks are gonna want to know that after 30 minutes of dark adaptation, their eyes are essentially dark adapted.
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Edited by EdZ (08/10/06 09:26 AM)
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EdZ
Professor EdZ
Reged: 02/15/02
Posts: 12341
Loc: Cumberland, R I , USA42N71.4W
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Quote:
From a practical standpoint, folks are gonna want to know that after 30 minutes of dark adaptation, their eyes are essentially dark adapted.
Well, that's kind of like saying from a practical standpoint people want to hear what they want to believe. What they want to hear is not always the complete answer.
edz
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Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
member#21
Edited by EdZ (08/10/06 09:27 AM)
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brentwood
professor emeritus
Reged: 11/04/05
Posts: 591
Loc: BC Canada
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I would put the recovery time of night vision at several hours based on personal experience. I went with the kids to the Mt Kobau star party in the sunny Okanagan valley. That first night the sky was incredible, darkest I'd ever seen. We didnt do an all nighter, we crawled into the tent at about 1am. At about 3am I left the tent for a nature call. The sky was now much darker, hard as it was to believe, I had trouble recognising the constellations.
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Big telescope.Small telescopes.
Ridiculous binocular collection
I've cut it twice and it's still too short.
Edited by EdZ (08/10/06 09:28 AM)
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rushintuit
sage
Reged: 04/01/06
Posts: 257
Loc: Farpoint Observatory
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Dear Professor,
The practical answer for dark adaptation of the human eye for the purpose of astronomical observation is 30 minutes. Knowing that rhodopsin continues to un-bleach for an additional 90 minutes, means that I will more closely guard my dark adapted vision in the field. When observing, I'm out standing in my field!
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Edited by EdZ (08/10/06 09:27 AM)
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Jay_Bird
professor emeritus
Reged: 01/04/06
Posts: 669
Loc: Nevada 36N 115W
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Based on some older relative's anecdotes, wearing good sunglasses in daylight (as listed above) and maybe even 'blue-block' or orange-amber shooting-type glasses worn as long as possible into dusk would help too.
Before a deck watch or night flight deep red goggles used to be worn for some time (maybe the 30 minute figure) in order to start dark adaption in normal light, and sunglasses were encouraged in daytime when night flying was planned.
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'these things stand like stone - kindness in another's troubles, courage in your own' Gordon
Edited by EdZ (08/10/06 09:27 AM)
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rushintuit
sage
Reged: 04/01/06
Posts: 257
Loc: Farpoint Observatory
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Good sunglasses would certainly help, but I think shooters glasses actually amplify incoming light.
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/// Stellarvue SV102ED /// Nikon 12x50 /// Fujinon 16x70 /// SkyTools 2 /// The Desktop Universe All Sky CCD Mosaic In Monochrome Mode ///
Edited by EdZ (08/10/06 09:28 AM)
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EdZ
Professor EdZ
Reged: 02/15/02
Posts: 12341
Loc: Cumberland, R I , USA42N71.4W
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Dark Adaptation discussion cut from another thread
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Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
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