So the last thing I want, is to be near unconfined lasers powerful enough to ionize the air.
I wholeheartedly agree. Just thinking about how the potentially-unregulated cheaply-manufactured knock-off projectors will result in having to wear welding glasses when walking around the street to avoid being blinded by the 3D advertisements that are being shot at your face...
I get that it's not good to tell the public "don't look at an eclipse unprotected except for this precisely-timed period," because that would lead to a statistically significant increase in permanent eye damage, but what we did seems to have gone fine, at least when exposures are circa once a decade.
I personally looked into the research on solar eye damage a few years ago (when the 2017 eclipse fervor had died down), and my impression is that all recorded cases result from focusing directly at the sun for at least several seconds straight; glancing very briefly at the sun, or seeing it in your peripheral vision, is only uncomfortable at worst. Eye damage is mainly associated with eclipses since they motivate many people to stare at the sun, rather than the partially-eclipsed sun being uniquely dangerous to look at. But when the time comes around, the messaging gets very black-and-white, as you said.
(Not that it's a bad idea to avoid looking at the sun as much as possible!)
> Eye damage is mainly associated with eclipses since they motivate many people to stare at the sun, rather than the partially-eclipsed sun being uniquely dangerous to look at.
Most sources seem to agree with that, and that's basically my impression. But I do know of another theory, which is that damage is associated with something like J/m² absorbed energy, and so roughly with (W/m² × s) of exposure, but the blink or discomfort reflex is associated with something more like total W entering the eye. The way that the sun is obscured during a partial eclipse is not by dimming (which would reduce both the total power entering the eye and the total power absorbed by a given region of the retina by the same factor), but instead by making a portion of the solar disc invisible, while leaving other portions fully visible. Those portions are still causing a comparable absorption of energy per second on the parts of the retina where they are focused, but the partially-obscured sun, in addition to being much more interesting, might be less uncomfortable to stare at because of the total amount of light being lower.
Sorry if that account was too wordy. A more concise way of putting it might be: Your desire to look away after a relatively short time is based on the total amount of light entering your eye (which is reduced during a partial eclipse), but the sun's ability to damage your eye is based more on the total amount of light focused on a given part of your retina (which is not reduced very much, since the parts of the sun you can still see are just about as bright as usual).
I don't know whether that interpretation is right, but it's another wrinkle on the "you're more inclined to stare at the sun during an eclipse than you usually would be" issue: it might not be exclusively because it's more interesting, but also because the total light is less than usual, so your discomfort is less than usual, but your risk of injury per second is only very slightly decreased.
Related to this, we don't have pain receptors directly on the retina itself, so the feeling of discomfort we get when looking at a bright light isn't directly indicating whether the retina is being damaged or not.
Your brain doesn't process "excess light" because your eyes aren't sensing visible light. They are being exposed to damage by the rest of the light, nonetheless.
The issue you mention does come up if you have a filter that blocks visible light but not UV. Non-UV-blocking sunglasses, for example, could increase the risk of cataracts compared to not wearing sunglasses at all (mainly because of pupil dilation).
Luckily I've never had any eye problems myself, but not for lack of trying. Back in elementary school, I would occasionally stare at the outdoor sun for 30 seconds or longer, just to see what could possibly be so bad about it.
Yet my eyes remain undamaged, at least as far as any optometrist has told me. Hence why I was skeptical about the supposed danger of eclipses. But perhaps the interval before damage can be much shorter, depending on age and other factors.
* latitude
* time of day¹
* individual genetics (maybe including something about the anatomy of your iris? or the focal abilities of your eye?)
* how fixedly you manage to stare at the sun, as opposed to letting your eye wander around a bit
* how frequently you unconsciously blink
that would cause the degree of injury to vary a lot. But it's understandable that experts would like to emphasize the really, just don't stare at the sun principle as the most reliable advice, so people don't do a lot of second-guessing (like "oh well I'm at a high latitude so it's not that bad").
I had also stared at the sun a little bit on occasion in elementary school (but for like 4-5 seconds, not like 30 seconds!) and that was one thing that gave me some counterproductive confidence that it wouldn't be super-harmful super-quickly.
¹ Notably, a lot of people will "watch the sunset" for like 1-5 minutes at a time, which is a form of starting at the sun, and I've never heard of that causing anyone any trouble. It really is true that time of day and latitude both have a big effect on the intensity of sunlight. Among other things, this interactive diagram makes pretty clear why watching the moment of sunset isn't that dangerous: https://engaging-data.com/solar-intensity/
It's easy to confirm there that the incident power in direct sunlight can vary by a factor of 100× as you get further from the tropics and closer to the moment of sunrise or sunset.
But it's not a great risk to have lots of people apply these heuristics to justify staring at the sun. If you just get a little bit confused about the details, the potential for damage is very, very high!
but I'm sure the welding glasses would fit the overall cyberpunk aesthetic of that future very well
Here's how to spot it:
Hold you hands together, with thumbs up, at arms length. Close your left eye, and slowly move your right thumb away to the right, while looking at your left thumb. At around 6 inches it will dissapear.
It's kind of hard to notice when my thumb is static, but it's more obvious if I wiggle my thumb while doing it.
They can, however, do an extended version of the blind spot experiment above for the whole field of vision, where they project light dots into a hemisphere in an unpredictable but iteratively somewhat exhaustive fashion. Very tiring and challenging test, since you need to keep your eyes from wandering, fixated at a boring reference point for more than half an hour. Like a hearing test, but for your eyes...
Laser beams or high energy radiation in general may also damage vision elsewhere in the optical pathway. Like opacification in the cornea or vitreous body when proteins get denatured by the heat. The body is very bad a repairing any damage in the optical apparatus since the eyes do have their own blood barrier, so macrophages usually don't have access to clean up "junk", and most tissues involved aren't really regenerative. Worse, damaged proteins tend to slowly spread the faulty structure to their neighbors.
Don't fuck with your eyes!
Your brain can fill in a lot of voids before you notice, especially for monotonous areas and static impressions (as mentioned the blindspot or the blood vessels on your retina are usually "invisible" until you provoke awareness through unusual lighting changes, or defined peripheral accounting experiments). You likely won't notice acquired "blindspots" looking at a white wall, or chaotic fallen leaves on the ground, especially where the other eye provides missing information, but at the edges of highly predictable patterns, one eye closed at a time, you may trick your brain to fuck up, eg. blur or indent otherwise clearly defined areas, when it can't decide which color to fill. Reading texts with on eye closed may also highlight "dancing" letters or distortions around your center of vision.
Worth noting, such defects may be caused by progressive conditions like retina detachment or even ocular melanoma, and the association with laser/light accidents may be incidental. If you spot a spot, do not brush it off as a limited loss! Have it checked, even with a likely attributable cause. You may prevent full blindness through medical intervention in case of disease!
Edit: You can see the blood vessels when you look a white wall and steadily move a (smartphone) flashlight in and out of the field of vision, slowly waving the light next to your head, illuminating from your ears to the side of your nose and consequentially your eyes at a shallow angle. This will cause an unusual blood vessel shadow, now meandering through your vision. The blood vessels are also very visible during eye examinations when the doctor moves the slit lamp around (go check it out ;)
Very weird seeing the insides of the very eye seeing, by ... well ... seeing.
Edit: Never mind; misread.
If you had say UV LEDs, all bets are off since it wouldn’t trigger the pupillary light reflex to close down the iris.
Make a grid in a drawing program with crosshairs in the centre. Close one eye. Keep looking at the crosshairs. Scan from the central focus point using your mouse and click when you can't see the mouse cursor. With a bit of trial and error you should be able to map out large regions you can't actually see in.
(My dad did this years ago for a retinal detachment spot in his one eye.)
More importantly: get an optometrist to check out your retina.
I have this spot in my right eye that resembles dead pixels. Just tiny blackness. If I let my eyes try to focus on it, it moves with my eyeball, so then they try to focus on the new location... ad infinitum. So they sort of jitter on a path upwards and to the right. I can only see it in certain lighting.
Eye doctor couldn't see anything wrong with the area and suggested it might be a floater that got attached and would go away on its own within 6mo. That was 4yr ago and it's still around. It's not getting worse so it doesn't bother me, it just reminds me of the saa from the Wheel of Time.
I would have expected interpolation versus vision artifacts as well, but apparently that's an "only sometimes" thing.
He reports it looking like a visible hole with surrounding distortion. Apparently similar to some renderings of black holes.
That said, this is a large defect in the centre of vision - it's pretty much un-interpolatable.
I understand smaller defects not in the macula just get interpolated away.
The mechanism isn't perfect and there are plenty of scenarios where your brain doesn't fill in the information, like the one I described. You also see it when looking at repeating patterns. It isn't something super obvious and if you choose to ignore it, it mostly goes away.
If your brain magically filled in the missing part of your vision in all cases, ask yourself how we would ever know that anyone has any amount of damage to their vision. Obviously we do know, since people talk about it. There must be some mechanism by which the damage becomes apparent to the patient.
Note: not an actual name, I don't know how these are called.
https://en.wikipedia.org/wiki/Humphrey_visual_field_analyser
Turns out, that I have a "pinhole" damaged area in the right eye's fovea. It's small enough that the brain can "interpolate" over it, especially when both eyes can see the object.