Foreground light, pupil constriction, color temp and color spectrum.

Reading a lot of posts and seeing many of the comments about foreground lighting, pupil constriction, etc. I would like to open up a discussion about this topic. I have posted this in automotive, but no doubt the topic could be interesting to fixed lighting w.r.t. street lighting.

FYI, my knowledge level is pretty high w.r.t. lighting, LEDs, eyes responses to light ... pretty good on street lighting ... tolerable on automotive, but not that high on automotive headlights beyond tolerable knowledge of the specifications.

For fixed lighting, I often preach to people the advantages of cooler color temperatures for any task oriented work as warm lighting can result in an unnaturally wide pupil opening causing a reduction in depth of focus leading to either bad/blurry focus or eye fatigue if moving between multiple focal depths, i.e. a screen and something else.

I have a friend who had one of the early forms of laser eye surgery which unfortunately only operated on a small circle of the pupil. She has no issues under bright light, but has night time driving issues as her pupil if fully dilated which results in weird optical effects as some of her vision is correct and some is not.

I was recently driving on a section of street that had newly installed LED fixtures. These were good quality fixtures and the lighting was even and I would say light beyond 70 degrees was well controller. The color temp I would estimate to have been 5500-6000K. I can't say i really liked the lighting very much. There was a sense the light was brighter, but could I honestly say I felt like I truly had better visibility and better ability to "see" ... no I could not. Something just did not feel right. For one, there was a sense of glare (and it was worse when I drove on that stretch when it was wet). This was a two lane each way divided road whose speed limit varied between 60 and 80 kph.

With the discussions about control of foreground lighting, it has made me think more about the effectiveness of different light sources, eye interaction, and how effective they will be mainly for high beams. I have had both HID and halogen car lamps, both in projector and standard implementations across a variety of vehicles. Probably the best high beam I have had was a projector style halogen. The best low was a HID.

I am interested in thoughts in this area, links to scientific papers, etc. I would think it is a good general topic.

In terms of LED headlights, perhaps sacrificing some CRI in order to decrease pupil decreasing wavelengths could result in the best overall implementation .... chop off everything below 500nm?

Semiman

This topic is heating up fast as LEDs' practical applications become broader. Mostly with past light sources we've been relatively tightly constrained with regard to the spectral power distribution of street lights and headlamps; selections were driven largely by available intensity, cost and efficacy. That's how we wound up with so much high-pressure sodium street lighting: very high efficacy, but lousy light quality.

White LEDs are giving us an unprecedented amount of freedom to tweak the SPD to optimize the quality of light for whatever task is at hand. But mostly we don't yet know what "optimal" really means. Scientists (real ones) are giving us conflicting findings so far. Likely much of the apparent conflict is just because there's a great deal we have yet to figure out; once the knowledge gaps start getting filled, the apparent conflicts will resolve. For example, it's been found that seeing performance is better under white LED street lights than under HPS street lights of equal intensity. It's been found that LED vehicle headlamps create the sense/feeling/impression of "brighter" light, and it's been found that they give poorer seeing performance compared to halogen lamps of equal intensity -- this would seem to speak to your experience with those LED street lights you mentioned. Mine too. It's been found that for equal intensity, higher-CCT white headlights create significantly higher discomfort glare without an accompanying improvement in seeing, and that lower-CCT white headlights create significantly lower discomfort glare without an accompanying degradation in seeing. The list goes on and on; right now there are more questions than answers, though there are plenty of vendors at every level of every sector of the lighting industry -- street, vehicle, household, office, etc. -- issuing cocksure pronouncements in (unsupported) scientific terms. There is a strong marketing/PR push towards "whiter" light (a more or less meaningless term most often referring to light that is bluer/has a higher CCT). The trope line is "Closer to natural daylight", though of course that is true only in the superficial, relatively trivial sense of apparent light color (CCT). The SPD of a metal halide lamp (such as an automotive HID headlamp) bears little resemblance to the SPD of sunlight.

As for headlamps: as long as we're realistically rejecting an extreme case (such as low-pressure sodium with a CRI of zero), CRI is not terribly important. That question was asked and rather satisfactorily answered in the early '90s when HID headlamps first came out: could drivers safely discern the important colors in the driving scene? UMTRI and others did good quality research on the matter and even though an HID headlamp's CRI is in the low-mid 70s (vs. halogen 99+), the HID headlamps give a driver perfectly adequate color vision. See here for example.

Your idea of chopping off everything below 500nm is a very interesting one. It's been done...for almost sixty years in France! Some of today's top scientists in the field are beginning to talk about how it looks like the French might very well have had the right idea, but at the wrong time -- the merits of removing the blue and violet from the output of vehicles' road lighting lamps would have been outweighed by the relatively primitive technology available at that time (intensity is king; color effects are subordinate -- headlamps of that era produced a lot less light than was needed for the task, so even relatively minor filtration aggravated the deficiency). The findings about the ability to worsen or lessen discomfort glare without affecting seeing performance by adjusting the SPD of white LEDs means we very well might have the choice of keeping glare levels fixed but increasing intensity for better seeing, or keeping intensity fixed but reducing glare for greater comfort and reduced fatigue. Will such an adjustment happen, though? That marketing push towards the bluer light is a very strong force and it remains to be seen whether it can be overcome, should the science point us in that direction. The marketer's definition of "optimal" is often out of step with the scientist's!

The "sermon" you preach (in favor of high CCT for reasons of pupil dilation avoidance) is an interesting one -- what science are you basing it on, please?

SemiMan said:

For fixed lighting, I often preach to people the advantages of cooler color temperatures for any task oriented work as warm lighting can result in an unnaturally wide pupil opening causing a reduction in depth of focus leading to either bad/blurry focus or eye fatigue if moving between multiple focal depths, i.e. a screen and something else.

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The bulk of what we look at when driving is much greater than 20 feet away, and for most eyes 20 feet is the same as infinity-- the depth of focus is pretty much the same at those distances. The occasional glance at the instrument panel aside, the eyes are going to be at infinite focus.

More tightly constricted pupils can help in certain problematic focus situations (hence a pinhole camera's ability to 'focus' so well), but similarly to a pinhole camera, the smaller the aperture the less light that is let in and the dimmer the image.

The shorter wavelengths of refract more sharply, and therefore in front of the retina, which is another reason blue light is problematic.

There are, of course, some good studies on the effect of light color that have been covered in our fog lamp threads.

Lastly, of course, is that the vision in night driving is not scotopic nor photopic, but mesopic. The type of lighting suited to that is very different, from, say, lighting needed while sitting at a bench repairing watches.

Alaric Darconville said:

the vision in night driving is not scotopic nor photopic, but mesopic. The type of lighting suited to that is very different, from, say, lighting needed while sitting at a bench repairing watches.

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Exactly so. And more than that: the task of a streetlight is far, far more different than the task of a headlamp than common sense might suggest.

Scheinwerfermann said:

The "sermon" you preach (in favor of high CCT for reasons of pupil dilation avoidance) is an interesting one -- what science are you basing it on, please?

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First I want to address Alaric's comment. I am in complete agreement. The best light for interior tasks is not related to what is best for low light level exterior circumstances including street lights and headlights. That brings us back to Scheinwerfermann's question.

A fairly recent development, i.e. < 10 years ago, has shown that pupil/iris response/opening is actually tied to melanopsin sensitive ganglion nerve cells which are a newly discovered third set of sensors within the eye. They are also primarily responsible for circadian rhythm.

Here is a good paper on mamalian melanopsin action spectra (mice): http://www.pnas.org/content/105/26/8861.full.pdf
A spectra for melatonin suppression related to melanopsin response: http://www.springerimages.com/Images/MedicineAndPublicHealth/1-10.1007_s10552-005-9013-6-1
Here is the spectral response in humans: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1945238/bin/nihms20390f4.gif
And the paper that this comes from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1945238/

Now overlay that action spectra with an incandescent/halogen spectra.

A very large portion of the photopic lumens of a halogen bulb and especially incandescent bulb do not excite melanopsin.

On a ratio basis, if you integrate the melanopsin action response curve with the spectrum of a halogen bulb, and 4000, 5000, and 6000CCT LEDS and/or metal halides, the higher CCTs sources, for an equivalent total photopic value, produce significantly more melanopsin action and hence cause greater constriction of the pupil/iris.

Now if you had 10,000 lux of halogen sourced light it would not matter as the pupil may be fully constricted. However, in the 200-500 lux that is common in an office environment and even at higher levels, a high CCT source will cause greater pupil constriction than the equivalent photopic brightness halogen or low CCT source.

As depth of field(focus) is a function of F-stop or iris opening diameter, the greater constriction, the greater depth of field and improved focus.

There is a great easy experiment for showing this. Set up equivalent brightness lighting in two very close areas. In one location use high a high CCT source (daylight fluorescents, LEDs) and in other use an incandescent bulb or better yet, do one office with daylight fluorescents and the other with 3K fluorescents as this will be easy to have similarly matched light levels. The 3000 has some blue spikes, the total energy is low below about 540nm. In the office with the high CCT source, get the smallest text item you can comfortably read at typical reading distances. Give your eyes about 5 minutes to adapt to this room. Now quickly go to the other office (seconds) with the low CCT source and hold that text at the same difference and keep looking at it. You will literally notice it blur in front of your eyes.


This all comes back to the discussion of spectrum, CCT, and forward lighting. A high CCT source will cause greater pupil constriction for equivalent light levels which would ultimately impact the ability to see far though traditionally most higher CCT light sources in automotive are also brighter. A bright lower CCT source may give the longest visibility distances or perhaps a tailored spectrum is even best.

What I don't have a good feel for is pupil constriction versus spectrum versus lighting level .... and to complicate that more, the combination of that and photopic/scotopic response.

I expect this may explain the issue I had with the high CCT LED streetlights. As I perceived them to be "brighter", that means they were stimulating more melanopsin as this impacts our perception of brightness. However, that also means they were probably stimulating pupil constriction. So, even though I perceived them to be brighter, less actual light was getting into my eye and as the levels may have been well into mesoptic if not photopic, the high CCT source was not providing any brightness benefit. It may have been making it worse. I just felt wrong if that makes sense.

In retrospect, mesopic and near photopic light levels at 6000K would not normally occur in nature except under absolutely nasty cloud cover. Hence, evolution would not have adapted for it.

Semiman

Hey Alaric, thanks for the pinhole camera analogy. This conversation finally gave me one of those "DUH!" epiphanies. I used to be a bit into photography, real 35mm before everyone went digital. I'm familiar with the concept of stopping down my aperture to increase depth of field. For some reason, I hadn't made the connection to the fact that as I get older I want not only my reading glasses to discern fine details, but lots of light. I whip the 4 Sevens Preon 2 out of my pocket and light up the subject.

As to foreground light vs distant vision while driving at night, I find myself wondering just how opened up my pupils really are when on that rural highway with high beams on. To what degree am I actually using night vision?

I know many drivers, my father included, say "Turn the dash lights down to the minimum you need to see the gauges, so you don't mess up your night vision."

But other drivers say "Night vision is what you use if you're driving only by moonlight. You lose that as soon as you turn on your headlights."

I've certainly seen examples where lots of light right in front of the car might momentarily fool a driver into thinking "gee I have really bright lights," until he realizes he can't see anything in the distance. For me, distance is what counts. Good headlights are something I really need. I recall a couple of embarrassing incidents when I was young; I drove to Everett, Washington, then got into the car at night and forgot to turn on my lights. Because I could see the lighted street and where I was going, the automatic "I can't see anything" reflex failed to prompt me to pull the headlight switch. Oops.

Experimenting with a powerful pillar mounted spotlight as a driving light, showed me that the relatively small amount of light spill onto the car/truck hood is enough close foreground light to be distracting (on the dark green car, it's tolerable until a layer of snow or frost amplifies it; on the faded gray truck with landing light spotlight at the top of the pillar, it was a nuisance anytime).

For me, pretty much any color temperature from standard incandescent headlights to the 4200-4300K "white" HID headlamps is fine. In fact, I like my yellow Cibie fog lights. My wife often wears yellow glasses in snowy or foggy weather. I just don't like anything "blue."

Salespeople like to say their lights are "closer to natural sunlight," but natural sunlight has to be a heck of a wide range. What you see at high noon in the desert is a lot different that what you see near sundown. And I have a hunch my human eyes evolved their night vision to use the kind of light that's present right after sundown.

This raises a lot more questions than it answers, huh?

Assuming a fuller spectrum light source, then full night vision, which is monochromatic, is tuned to a fairly high CCT light source, one could assume specifically moonlight. That would contrast with the low CCT of sunlight right after sundown which is still full color vision.

Semiman

SemiMan said:

Assuming a fuller spectrum light source, then full night vision, which is monochromatic, is tuned to a fairly high CCT light source, one could assume specifically moonlight. That would contrast with the low CCT of sunlight right after sundown which is still full color vision.

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But again, those are at the scotopic and photopic ends of vision. Scotopic vision is very low acuity vision, photopic vision is high acuity. While the rods are sensitive to blue light, the appearance of light is not alone to see -- we need detail. We're not crepuscular animals, and definitely not nocturnal -- we're diurnal animals.

Alaric Darconville said:

But again, those are at the scotopic and photopic ends of vision. Scotopic vision is very low acuity vision, photopic vision is high acuity. While the rods are sensitive to blue light, the appearance of light is not alone to see -- we need detail. We're not crepuscular animals, and definitely not nocturnal -- we're diurnal animals.

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Completely agree.

I remember reading some interesting article recently about how at even fairly low light levels the two detection systems in the eye can work in concert to increase acuity and provide a level fo color detail. "Night" vision, at least the sensititivity factor chemically degrades quickly as light levels increase, but I am not finding good data on pupil dilation at the same time and spectrum data related to that.

SemiMan said:

A fairly recent development, i.e. < 10 years ago, has shown that pupil/iris response/opening is actually tied to melanopsin sensitive ganglion nerve cells which are a newly discovered third set of sensors within the eye. They are also primarily responsible for circadian rhythmrl]

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Good stuff, based on a quick skim. I'll need to read this paper and scrutinize the figures more thoroughly than I have time to do right now. It is interesting to consider this newer science on a backdrop of P. Devaux' 1970 paper describing a physiological mechanism by which removing the blue-to-violet from headlights makes things better.

the higher CCTs sources, for an equivalent total photopic value, produce significantly more melanopsin action and hence cause greater constriction of the pupil/iris.

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...which gives rise to some interesting hierarchy-of-effect questions that boil down to "what are the net practical effects on seeing and glare under mesopic night-traffic conditions?". This looks like one of the knowledge gap-induced apparent contradictions I mentioned in post #2: one would think a stronger pupillary constriction response would attenuate discomfort glare, but we have robust findings that higher blue content in headlight ==> higher discomfort glare.

(you may notice I try to shy away from referring to CCT. This is because it is very often inappropriately used when the actual salient aspect is SPD. The two are of course correlated, but they are not synonymous and in the context of road illumination for driver seeing performance, SPD is more directly apposite.)

As depth of field(focus) is a function of F-stop or iris opening diameter, the greater constriction, the greater depth of field and improved focus.

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Sure, but I am guessing this probably does not fully countervail the problems the human eye has coping with blue light.

traditionally most higher CCT light sources in automotive are also brighter.

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"Traditionally" here must refer to HID headlamp light sources. I would quibble with your use of "brighter" -- brightness is a subjective measure. Replace "brighter" with "more intense" and I no longer have a quibble. That aside, yes, with white LEDs we now have the never-before-tried combination of relatively high blue content ("high CCT" if I must) and relatively low intensity.

A bright lower CCT source may give the longest visibility distances or perhaps a tailored spectrum is even best.

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I have no crystal ball, but I'm fairly confident that yes, a tailored spectrum will eventually be derived that will optimize the situation, and we'll be talking in much finer-grain terms than "seeing vs. glare". Intensity is by far the foremost determinant of seeing performance; it swamps secondary factors like SPD. All these fixed-intensity, variable-SPD experiments are headed, in the long run, towards figuring out what the optimal spectrum looks like.

What I don't have a good feel for is pupil constriction versus spectrum versus lighting level .... and to complicate that more, the combination of that and photopic/scotopic response.

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I think we'll have considerably better knowledge to answer this question in the next 5-10 years. We also don't really know for sure what is the causal chain behind the physical discomfort caused by glare, and a hard answer to that question has been eluding researchers for quite awhile.

I expect this may explain the issue I had with the high CCT LED streetlights. As I perceived them to be "brighter", that means they were stimulating more melanopsin as this impacts our perception of brightness. However, that also means they were probably stimulating pupil constriction. So, even though I perceived them to be brighter, less actual light was getting into my eye and as the levels may have been well into mesoptic if not photopic, the high CCT source was not providing any brightness benefit. It may have been making it worse. I just felt wrong if that makes sense.

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You're certainly not alone in what you perceived, and your supposition of the causal chain passes at least my sniff test. One thing is very clear: the marketing line about "whiter brighter closer to daylight for better seeing" is a load of hooey!

In retrospect, mesopic and near photopic light levels at 6000K would not normally occur in nature except under absolutely nasty cloud cover. Hence, evolution would not have adapted for it.

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Yeah, a very large proportion of what human factors and traffic safety researchers spend time on is figuring out how best to adapt the human animal to a set of circumstances for which we are evolutionarily utterly unprepared.

Great conversation we've got going here. At least I'm enjoying it!

Scheinwerfermann said:

I think we'll have considerably better knowledge to answer this question in the next 5-10 years. We also don't really know for sure what is the causal chain behind the physical discomfort caused by glare, and a hard answer to that question has been eluding researchers for quite awhile.

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I am going to "wager" and operational theory for this one which of course could be completely wrong, but may be right.

Facts:

- Blueish light or at least light primarily below 520nm is required to constrict pupils
- Scotopic vision is "designed" for <5 lux
- Scotopic vision is more sensitive to the blue end of the spectrum
- The ganglion nerve cells are distributed across the retina
- Pupil response is not instantaneous
- When I walk to bright sunlight I get "glare" and a pain sensation not unlike a badly aimed 6000K HID conversion coming right at me ... or a super bright poorly controlled 6000K HID or LED outdoor fixture
- Much of the outdoor built environment, at least when we are driving (including our car and others), is lit with sources deficient in blue whether that is halogen headlights, HPS street lights, or and heck even the 4000K metal halides in cars and typical for parking lots are not that high in <520nm output


So my theory is as simple as:

- Pupils typically widely dilated due to the lack of bluer wavelengths in typical lighting
- Night vision fairly "active" again due to the lack of large amounts of blue light


When you are suddenly hit with an intense light source with a spectrum rich in light towards the blue end of the spectrum two things happen:

- Rods overload
- Brain sends a signal that says hey, it's a heck of a lot brighter than I thought it was (due to said ganglion nerve cells), which causes the pupil to close and perhaps also the safety mechanism of trying to look away to prevent eye damage



Oh, that brings me to my other quick experiment to show that pupils constrict more with a richer blue spectrum light environment. Go back to those same offices described above and after waiting 5 minutes for your eyes to adjust, look directly into a flashlight (not too bright of course). In the high CCT office, the flashlight will not seem as bright when you look at it... or you could say the glare is less which may support my theory above.


Semiman

SemiMan said:

For fixed lighting, I often preach to people the advantages of cooler color temperatures for any task oriented work...

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I've always been a fan of incandescent lighting when it comes to normal room lighting or general usage, but when it comes to, as you say 'task oriented work', definitely have always preferred flourescent, and recently my cooler tinted LED lights.
Of course, this has no relation with my feelings when it comes to throwing light down the road and I'm once again, firmly in the group who prefers my headlights to throw no dazzlingly dangerous blue at other drivers.

I can't speak to much of what you guys are talking about here, but plan on reading and learning from our group of CPF professors - carry on, please.

Hamilton Felix said:

I know many drivers, my father included, say "Turn the dash lights down to the minimum you need to see the gauges...

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I turn my dash lights down, but the reason for me is the same as what you mentioned about foreground light and its tendency to be distractive and not helpful. Great post by the way.

I don't see anything unreasonable about your idea, but it doesn't head in the direction of explaining the pain sensation that gives discomfort glare its name, and that's what isn't yet(?) understood.

Hamilton Felix said:

many drivers, my father included, say "Turn the dash lights down to the minimum you need to see the gauges

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Good advice. We classify glare as "discomfort" ("psychological") or "disability" ("physiological"). These categories are not synonymous with imaginary/real or important/unimportant, and one thing that doesn't occur to a lot of people because it's counterintuitive is that it's not the case that glare up to a certain level is "only" discomfort glare and above that level is disability glare. It's actually the other way around: any light source in the visual field diminishes the eye's dark adaptation, thereby degrading visual acuity -- i.e., there is always some amount of disability glare. There may or may not also be discomfort glare.

Every bit of disability glare that can be removed is of benefit to the visual acuity, so yeah, turn down the dash lights. Unfortunately that won't do a thing about massively overlit billboards and gas stations and jumbotrons.

I've certainly seen examples where lots of light right in front of the car might momentarily fool a driver into thinking "gee I have really bright lights," until he realizes he can't see anything in the distance.

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You're giving most drivers far too much credit here. The strongest correlate by far between headlamp performance and subjective headlamp ratings is foreground light. The human visual system just doesn't evaluate its own performance very accurately. For most drivers, there is no cognizance that they cannot see anywhere near as well as they feel like they can. That's actually true even for the best possible low beam headlamps for simple reasons of geometric limitation to seeing range combined with prevailing road speeds, but now I'm departing from the real topic at hand.

I drove to Everett, Washington, then got into the car at night and forgot to turn on my lights. Because I could see the lighted street and where I was going, the automatic "I can't see anything" reflex failed to prompt me to pull the headlight switch.

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That has gotten worse with headlight-type daytime running lights and always-illuminated dashboard displays.

Salespeople like to say their lights are "closer to natural sunlight," but natural sunlight has to be a heck of a wide range. What you see at high noon in the desert is a lot different that what you see near sundown.

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Sure, but the bigger difference than the color is the nature of the light. Continuous spectrum vs. spikes and troughs.

This raises a lot more questions than it answers, huh?

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That is the true nature of science!

I look at it from an evolutionary stand point, along the lines of what we're adapted to mentioned a few posts up.

Essentially, our eyes can be more damaged by ultraviolet light, say from looking at the sun...so we are hard wired to constrict the pupils to protect our eyes from UV damage.

As we cannot see in the UV spectrum...that translates to bluer light causing constriction as a proxy. It would not surprise me if we HAD some UV sensitivity that we simply needed to tweak to sense consciously. Even if we could not see with it, there could be receptors that could tell us its "there", and so forth. Of course, any strong light (Intensity rather than just wavelength related...might be damaging as well....and if nothing else, would have caused our ancestors to lose the ability to see on a temporary basis due to strong reflection glare, etc.

So there might be some bands of sensitivity designated as triggers.

The recent discoveries of third receptors in some people would be an example of us not really knowing everything about how our eyes work. Not only do people with this genetic variation have different night vision, but they can perceive more selective color differentiations. (As in being able to essentially "see more colors than the rest of us")

As also mentioned...we are diurnal, and not really designed for nocturnal work. We DO have some ability to see in low light scenarios, and from an evolutionary stand point, whatever starlight and moonlight might have provided, would have been the most advantageous light to see by, as that's all there was when we were busy evolving.

If you ARE night adapted...you can't really see colors much anyway, as the parts of your eye that sense colors are pretty much uninvolved...and so is your fovea for the same reason.

The part with the most acuity and resolution is the worst in low light. If we are creeping around in the dark by starlight...what color things are is not going to be very clear. The MIND will fill in whatever color you think it SHOULD be when you see a pine tree or a shirt, etc. As in you will "see" the pine tree as green because you know its supposed to be green. If Bob was wearing a red shirt when he walked away from you...and you then see Bob off in the distance, you will see his shirt as red....even if Bob changed to a green shirt to test your color vision at night.



My understanding of discomfort glare does seem in line with the idea that the exact same light will cause discomfort if your eyes are adapted to low light, and might be too dim to see by if fully light adapted.

I have a mental image of the pupils perceiving that I am staring into the sun or catching the glare of the water, etc...and slamming shut so hard that it hurts when starting from a wide open aperture.

I think we are generally hard wired for certain incoming signals. It may go back to when we were more primordial/single celled...but rejection of incoming overwhelming stimuli occurs in other fashions too.

If I go outside into bright sunlight, especially if there's snow cover, etc......I might sneeze. I think my "inner amoeba" senses an overwhelming stimulation, and fires an ejection signal. That signal is translated to a sneeze eons after it perhaps was connected to a more relevant response. Sneezing of course no longer makes any sense in that scenario...but, I think I'm stuck with it as an evolutionary adaptation that remained in my wiring.

Interestingly...I don't recall myself or other sneezing if an oncoming car's headlights are too bright, or someone shines a flashlight into their eyes.

It also seems to only occur when I first go outside...I don't KEEP sneezing, etc.


THAT means its not JUST the glare. Its AN ASPECT of the glare that is triggering the sneeze response.

PART of it must be the CHANGE - as the sneezing is temporary...and stops upon adjustment.

The rest must be related to a characteristic of bright daylight that is absent from artificial light.

If this proves to be due to the missing wave lengths it would be nice. Its likely a combination of wavelength or range of lengths with some threshold of intensity are involved.



It does make me wonder if the glare/intensity of a flashlight or other artificial light source beam could be made strong enough, or possessing whatever characteristic is needed to also cause sneezing.

Scheinwerfermann said:

I don't see anything unreasonable about your idea, but it doesn't head in the direction of explaining the pain sensation that gives discomfort glare its name, and that's what isn't yet(?) understood.

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I think it does explain discomfort glare. Essentially the melanopsin sensitive ganglian cells are saying "too bright" and to TEEJ's post either it is the fast physical constriction that is causing pain or sensations of pain, and/or it is an evolutionary pain like response to protect the eyes from bright light. We are evolved to respond quickly to pain.

It would be interesting to do an experiment that shined melanopsin normalized brightness light sources at the eye under low average illumination and see if the discomfort glare response was similar. The background illumination could also be done at a fixed photopic/mesopic level but with light sources of differed spectrums to determine that access of response.

Semiman

SemiMan said:

I think it does explain discomfort glare.

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As I say, I don't see anything unreasonable about your think-through on the matter, but AFAIA scientists and doctors who devote their careers to studying the eye don't think that's the mechanism linking glare to pain, and I have to defer to them because their conclusion (or, more to the point, their lack of conclusion) is based on research and data. Yours is based on assumption and supposition. Given how infrequently the world (let alone the human body) works in accordance with the ways "common sense" suggest it should, it's appropriate to maintain a high wall separating guesses, opinions, suppositions, hypotheses, common knowledge, common sense, received wisdom, and the like from established facts, data, and supportable conclusions.

SemiMan said:

I think it does explain discomfort glare. Essentially the melanopsin sensitive ganglian cells are saying "too bright" and to TEEJ's post either it is the fast physical constriction that is causing pain or sensations of pain, and/or it is an evolutionary pain like response to protect the eyes from bright light. We are evolved to respond quickly to pain.

It would be interesting to do an experiment that shined melanopsin normalized brightness light sources at the eye under low average illumination and see if the discomfort glare response was similar. The background illumination could also be done at a fixed photopic/mesopic level but with light sources of differed spectrums to determine that access of response.

Semiman

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I can only hypothesize that the 'pain' is from the forced rapid production of rhodopsin, which will photobleach and be depleted rapidly. But I'm not an optometrist or opthalmogist, so it's just a hypothesis.

Speaking of evolution-- we're driving around at night at speeds of 65mph and sometimes faster-- it wasn't until the 1900's that we regularly exceeded about 25mph and had to do all our own course corrections (driving). (Horseback riders would go about as fast or faster, but the horse itself would do all the brainwork to deal with variations in terrain and collision avoidance.)

Alaric Darconville said:

I can only hypothesize that the 'pain' is from the forced rapid production of rhodopsin, which will photobleach and be depleted rapidly. But I'm not an optometrist or opthalmogist, so it's just a hypothesis.

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And it sounds just as good and passes the reason test just as easily as the rapid-physical-constriction hypothesis...which is why we still have to wait for an actual, robustly supported answer, frustrating though that wait is.

Alaric Darconville said:

I can only hypothesize that the 'pain' is from the forced rapid production of rhodopsin, which will photobleach and be depleted rapidly. But I'm not an optometrist or opthalmogist, so it's just a hypothesis.

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Scheinwerfermann said:

And it sounds just as good and passes the reason test just as easily as the rapid-physical-constriction hypothesis...which is why we still have to wait for an actual, robustly supported answer, frustrating though that wait is.

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And even that depends on how important the research really is compared to eye diseases, or other advancements that can be made in automotive lighting itself. (However, this could have some military applications...)