# Is it dangerous to look into bright lights?



## SCblur (Mar 3, 2006)

I've heard this at times here on the forums. Is it true that looking into really bright lights is bad for you? How bad? How bright would a light need to be before it is dangerous? Am I safe looking into my A2 and G2, or is that stupid? I never thought this would be harmful until I came here.


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## this_is_nascar (Mar 3, 2006)

SCblur said:


> I've heard this at times here on the forums. Is it true that looking into really bright lights is bad for you? How bad? How bright would a light need to be before it is dangerous? Am I safe looking into my A2 and G2, or is that stupid? I never thought this would be harmful until I came here.



With all due respect............... what do you think the answer is? Isn't the answer similar to "is it dangerous to walk in the street with moving traffic"? No disrespect intended, but come on.


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## Justice Inc. (Mar 3, 2006)

First of all I must admit that I am no expert, but I don't think that looking into bright lights on a regular basis would be all that good for your eyes. Just like staring at the sun - if you do it for long enough something will give. But seriously I think that it would be best practice to avoid it (looking at the sun and into bright lights).


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## Mini-Moder (Mar 3, 2006)

I agree with TIN on this one. But if you just got your A2 or something and you wonder how bright it is, I dont think it is oging to hurt you just that once. But if you do it everyday, I would imagine after a while it would casue damage.


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## zespectre (Mar 3, 2006)

From my own research what you have to be especially careful of is light in the blue or violet end of the spectrum (the shorter wavelengths) which, above a certain power, can cause photochemical issues in the retina. It is also possible to actually burn the retina or other parts of the eye from a very concentrated beam (such as viewing the sun through a telescope or a strong SLR camera lens).

There are several flashlights that are capable of that sort of output when placed close to the eye and looked at directly.

Apparently this damage is almost never irreversable but are you willing to risk your vision on "almost"? Also, bright lights cause a pain response. This is your body protecting itself and you should listen.


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## adirondackdestroyer (Mar 3, 2006)

Well I have heard that looking into LED's is worse for your eyes and looking into Incandecent lights, but I'm not sure. 
I myself have looked into all of my lights, not from 6" from my face, but I have someone shine them at me at around 30 feet, so I know how they would appear if I were to shine them at another person at a distance that is possibly approaching me. The light isn't physically painful, but it defintely doesn't feel pleanant either.


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## Solstice (Mar 3, 2006)

zespectre said:


> From my own research what you have to be especially careful of is light in the blue or violet end of the spectrum (the shorter wavelengths) which, above a certain power, can cause photochemical issues in the retina. It is also possible to actually burn the retina or other parts of the eye from a very concentrated beam (such as viewing the sun through a telescope or a strong SLR camera lens).
> 
> There are several flashlights that are capable of that sort of output when placed close to the eye and looked at directly.
> 
> Apparently this damage is almost never irreversable but are you willing to risk your vision on "almost"? Also, bright lights cause a pain response. This is your body protecting itself and you should listen.



Any intense light source is dangerous, but I have also read the blue light is 100 times more dangerous than red. That's not an invitation to stare into bright red lights . I agree that anything that induces wincing, squinting and eye pain can't be good for you. Note that because white LEDs contain more blue than most other colors, they might bad for long periods of time. I do notice more eye fatigue when reading with bluer 5mm light as compared with the warmer tint of an underdriven luxeon.


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## JonSidneyB (Mar 3, 2006)

I looked into the beam of a Surefire Beast at the Ghost Mountain trip. Not sure why I did that. I survived it but I do not recomend it.


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## tron3 (Mar 3, 2006)

I've done this from a distance. Your iris are made to contract with such painful light, but it's not 100%. Occasional blasts will not hurt you, but dont do it at all if you can help it.

Best way is to look at the reflected beam off the wall. Or, put on good sunglasses and quick glance from a distance.


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## SCblur (Mar 3, 2006)

Okay, let me clear this up in my defense. I'm not that dumb. Mind you, before I cam here, the brightest light I knew of was a mag. And no, I don't look into my lights for fun. And yes, it makes sense to me that tactical, bright lights would not be good for you. I'm just wondering how bad they would be. At what brightness level do they begin to be damaging? Don't worry, I am playing with a full deck.


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## JonSidneyB (Mar 3, 2006)

2900 lumens were enough for me. I really don't know what I was thinking...I tried to deny doing it but there were too many witnesses. Don't do this.


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## Yooper (Mar 3, 2006)

Alright then. This is my job (MD, ophthalmologist). You can permanently burn your retina with any bright light source, but it takes a lot of light and it usually takes some prolonged exposure. For example, stare at the sun on a bright day for about ten minutes straight and you'll almost for sure do some damage. A few seconds exposure to any flashlight that's not a laser is unlikely to do permanent damage, but there are plenty of flashlights out there that would do it with a prolonged exposure.

Just use common sense. If it hurts, don't do it. :ironic:

Short wavelength can be more damaging, yes. If you expose yourself to bright UV light like an arc welder for more than a few seconds you're going to get a surface burn, basically sunburn, on your corneal surface. Usually this heals up just fine after a few days.

However, long wavelength light can do damage as well. Glass blowers used to get weird cataracts in the old days from the infrared (heat) radiation from their work...


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## this_is_nascar (Mar 3, 2006)

SCblur said:


> Okay, let me clear this up in my defense. I'm not that dumb. Mind you, before I cam here, the brightest light I knew of was a mag. And no, I don't look into my lights for fun. And yes, it makes sense to me that tactical, bright lights would not be good for you. I'm just wondering how bad they would be. At what brightness level do they begin to be damaging? Don't worry, I am playing with a full deck.



I understand that and like I said, no disrespect was intended. My take is that if causes your pupil to dilate, it must produce some level of harm. Now, saying all that, I can't stand here and say I've never intentionally blasted myself with a bright light.


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## Lexus (Mar 3, 2006)

If the body is sending the signal "discomfort" when you look into a bright light, better listen to your body, you only have ONE set of eyes.
Short wavelengths (blue, violet) cause more harm than longer ones. UV is probably the scariest: You can't see it, your pupils stay wide open, letting all the light into your eyes. 
Did I flash myself into the eyes? Heck, yes! But I don't stare into bright lights too long. I still want to play with flashlights when I'm an old man.


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## Paul_in_Maryland (Mar 3, 2006)

SCblur said:


> Okay, let me clear this up in my defense. I'm not that dumb. Mind you, before I cam here, the brightest light I knew of was a mag. And no, I don't look into my lights for fun. And yes, it makes sense to me that tactical, bright lights would not be good for you. I'm just wondering how bad they would be. At what brightness level do they begin to be damaging? Don't worry, I am playing with a full deck.


You're right, SCblur, your question wasn't stupid, and the answer isn't obvious. 

For those who missed the point of his question, SCblur wants to know, "At what point does 'causes discomfort' cross the threashold into 'causes permanent damage'?" 

As several CPFers have pointed out, damage and discomfort are, in part, frequency-dependent. I think that a second factor is "lumens per unit of arc" of our cone of vision. Let's face it: 1,000 lumens coming from a photographer's light umbrella would probably be tolerable. 1,000 lumens from a tactical flashlight could well cause permanent damage.


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## dcarch8 (Mar 3, 2006)

I think it depends a little on the frequency components (color) of the light, and then on how coherent is the lightwave of the source of the light.

If the light source is coherent, as in laser beam, you will be in a much bigger trouble because the light energy can be fucused into a much smaller spot on your optic nerves.

Say, you are not a moth, are you?


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## Navck (Mar 3, 2006)

JonSidneyB said:


> I looked into the beam of a Surefire Beast at the Ghost Mountain trip. Not sure why I did that. I survived it but I do not recomend it.


 
Nutwing award!


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## Lee1959 (Mar 3, 2006)

It is especially dangerous if you look into the beam of your Surefire M6 while driving at night on a busy two way highway...I only look into bright lights for a few seconds when I really feel the need to sneeze, yes sneeze, lol. I have very light sensitive eyes, I think I can see in the dark better than most people but in sunlight I have to wear sunglasses almost constantly to see, and not to sneeze constantly. Something in bright light makes me sneeze like crazy. I will probalby sneeze half a dozen times walking out of the house to my truck before putting on my sunglasses on a sunny day, and it is worst in winter.


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## dfred (Mar 3, 2006)

That is called the photic sneeze reflex...


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## cratz2 (Mar 3, 2006)

Well, it certainly can't HELP anything...

Last bright light I looked into was a direct driven T3JG green Lux III. I saw a dark spot for the next two hours.

I repeat, that is the LAST BRIGHT LIGHT I looked into...


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## thezman (Mar 3, 2006)

This falls into the catagory of:

Hey dude, hold my beer while I............


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## Yooper (Mar 3, 2006)

this_is_nascar said:


> My take is that if causes your pupil to dilate, it must produce some level of harm.




Huh? You meant constrict. Try this experiment: grab your weakest, dimmest light source. Go to your bathroom and turn on the ceiling light. Look in a mirror at your pupils. Shade one eye from the ceiling light. Your pupil with dilate. Shine the weak light into your eyes, maybe bouncing it off the mirror. Your pupils will constrict. They constrict and dilate continually all day in response to ambient light levels. ANY LIGHT will make your pupils constrict. 

I was going to give you all a nice dissertation on this subject now that I'm home and have the time, but apparently you're not paying attention, so I won't waste my time. :shrug:


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## Handlobraesing (Mar 3, 2006)

I think it would depend heavily on the state of your pupils. 

When you're adapted to bright sunlight outside, the aperture is small enough that it might not be harmful, but if you do it after you've been sitting in the darkness for two hours, it could be harmful. 

I dunno


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## Yooper (Mar 3, 2006)

:huh2:     :lolsign:


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## CroMAGnet (Mar 3, 2006)

I just read this for the first time and was surprised at the way this thread evolved right from the 2nd post.

Last year I had one of my first eye exams with an actual doctor. I'm lucky to have excellent vision but I will probably need reading glasses when I'm old(er)

Anyway, I was a budding flashaholic and innocently asked him if flashights can be dangerous to your eyes. I was prepared for an technical recitation of the dangers of why it was harmful but he simply said it wasn't. So I said "Are you sure?" and pulled out one of my lights, can't remember which, still without hesitation he maintained that it wasn't harmful, giving me the sense not to worry about it. Should I get a second opinion? 

Obviously he doesn't know about Flashaholics


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## JimmyB (Mar 3, 2006)

Yooper said:


> I was going to give you all a nice dissertation on this subject now that I'm home and have the time, but apparently you're not paying attention, so I won't waste my time. :shrug:


 
Come on Yooper, some of us are paying attention. One of the things I like about CPF is the wide range of knowledge. It's nice to have an MD (Opthalmologist no less) chime in. I appreciated your posts about night vision not too long ago. If you're still willing, many of us would love to hear what you have to say and I promise I'll pay attention.

JimmyB


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## spyderknut (Mar 3, 2006)

Yooper said:


> :huh2:     :lolsign:


 
Thanks Yooper! I don't know many people who have NEVER looked directly at the sun. I don't have any lights (yet) that create a bright spot on the ground on a sunny day. I figure very bried and infrequent glances ain't hurting much. There are some out here who understand and appreciate you input.


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## LuxLuthor (Mar 3, 2006)

Yooper, interesting info. 

You might want to expound on why UV light even at low levels (i.e. in haunted house amusement parks) can cause a sensation of discomfort, and why at bright intensity levels (arc welder) UV burns the cornea, but not the lens or retina.

Does that long exposure staring at the sun (which I assume would be a similar effect to some of the bright flashlights/spotlights) only do retinal damage (given that skin sunblocks mainly block UV rays, makes me wonder why not corneal damage like the welder arcs)?

Also, why certain laser colors burn the retina and not the cornea &/or lens, and what medical lasers (& wavelength types of them) are doing in various eye surgeries (good use of lasers).


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## michiganstud (Mar 4, 2006)

SCblur said:


> I've heard this at times here on the forums. Is it true that looking into really bright lights is bad for you? How bad? How bright would a light need to be before it is dangerous? Am I safe looking into my A2 and G2, or is that stupid? I never thought this would be harmful until I came here.


 


I'm not a regular here, but I just have to say ..... why would you WANT to look into your light? I don't get it.


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## LuxLuthor (Mar 4, 2006)

michiganstud said:


> I'm not a regular here, but I just have to say ..... why would you WANT to look into your light? I don't get it.


 
Oh you haven't heard? It's a new Zen Buddism sect, seeking immediate enlightenment. The master issues his shaktipat with a modded maglite.


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## yazkaz (Mar 4, 2006)

Well I've done this many times. I used to shine my M3 right into my eyes to determine if the levels have dropped and batteries need to be changed. Of course I can feel the heat of the beam so I only do this in very short periods of time (of course, I don't want to burn out my retinae). I eventually repeat the same practice on LED flashlights, with these lights I can easily tell if the levels have dropped simply by looking into the beam and the emitter.

BTW I have eye problems so every year (or two) I have my eyes checked by an ophthalmologist. Suddenly the experience of looking into the M3's beam becomes nothing -- with the actual eye checkup my pupils are dilated followed by high intensities of light (cold light) shone right into the retinae, which is MUCH MORE painful IMHO.


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## tron3 (Mar 4, 2006)

LuxLuthor said:


> Oh you haven't heard? It's a new Zen Buddism sect, seeking immediate enlightenment. ....


 
Q: What did the Zen Buddist say to the hot dog vendor?
A: Make me one....<touches finger tips and bows head> ...with everything.
:laughing:


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## fixman88 (Mar 4, 2006)

I remember a while back while I was on the way home I was sitting in the left-turn lane directly opposite a BMW with the brightest headlights I ever saw (in the daytime, no less)! I had to lower my sun visor to keep from being blinded! When I finally turned I glanced over to see if the BMW's brights were on. They weren't.


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## Yooper (Mar 4, 2006)

OK, but if one more knucklehead says "I think it depends on your pupil" I'm done.

As we all know, or should know, there is a wide spectrum of light. Most thermal radiation sources, like the sun and incandescent bulbs, will put off almost a full spectrum of light, from deep infrared (heat), which is low frequency and long wavelength, all the way up beyond ultraviolet and into microwave and X-ray frequency, which is high frequency and short wavelength. Of course each radiation source will have a peak at a certain spot on the spectrum and the amount of energy put out will fall off toward the ends of the spectrum. Something like an incandescent bulb will overwhelmingly radiate in the infrared to high frequency visible range, with very little UV or higher frequency put out.

Tissue damage is from energy being absorbed by the tissue, and each kind of tissue will absorb certain frequencies more than others. I should present some very basic eye anatomy next, as many people have no concept of it. Here is a very simple diagram of the eye if it was cut in half in a sagittal (vertical) plane:






Light comes in through the cornea, which is clear, through the pupil, which is a hole in the center of the iris, through the lens, which is clear, and is focused by this optical system onto the retina, which lines the back of the eye. The retina has an array of photoreceptors, which each sense something similar to a pixel of light and send a signal through a complex nerve network that comes together in the optic nerve to send visual info to the brain.

So, the cornea and lens are clear, so they do not absorb very much visible light, instead transmitting it and focusing it on the retina, which absorbs most of it. There is a layer of pigmented cells behind the photoreceptor layer of the retina that absorbs just about everything. Therefore the retina can be damaged by pretty much any wavelength of light that reaches it and is intense enough to cause a burn. 

When tissue absorbs light energy that energy is mostly converted to heat. Enough heat will cause a burn.

So now we can look at what happens to different wavelengths of light. Infrared light is absorbed to some extent by the cornea and lens, but some of it makes it to the retina - the longest wavelengths (heat) are absorbed mostly by the cornea, but the near infrared mostly makes it to the retina. So a near infrared laser for example will cause a retinal burn easily, but something that is mostly putting out heat energy will cause a surface burn first.

Visible light makes it through the cornea and lens almost completely and is FOCUSED on the retina. So a very bright and very small visible light source can cause a small burn to the retina.

Higher frequency light will somewhat absorbed by the cornea. Again those wavelengths that are near to visible will make it to the retina, but the super short wavelength far UV light (also called hard UV) will be absorbed by the cornea and the lens. This is why a welding arc causes a corneal burn right away - the hard UV light will be absorbed by the cornea and so won't make it to the retina to cause damage. You can however still get some retina damage from a welding arc if there is a long enough exposure. UV light exposure is a know risk factor for cataract formation (lens damage) and may be a risk factor for age related macular degeneration (retinal damage). 

There is also evidence that bright blue light (like laser scatter) is quite damaging. Ophthalmologists no longer use blue lasers for this reason.

So, for each tissue there is a certain amount of light energy that will be intense enough to cause a burn and therefore permanent damage, and each tissue absorbs different wavelengths differently, plus each tissue has some built in cooling system - the cornea has fluid behind it, and the retina has a very active blood flow keeping it cool.

Adding to the complexity a little bit is the pupillary response. Your pupil will constrict in bright light, limiting how much light gets in, but it only responds to visible light, not to IR or UV, because it's constriction is triggered by the optic nerve sending a signal into a reflex loop of nerve connections. A bright IR or UV source that doesn't also have a bright visible radiation will not trigger the pupil. This is why sunglasses can be dangerous if they don't block IR or UV - the dark glasses cause your pupil to dilate, letting in more IR and UV than if you weren't wearing them.

Sometimes the damage can be microscopic and cumulative, so you don't notice it until you get a cataract or macular degeneration or you might just have some night blindness or something or just not quite as good contrast sensitivity as you used to. Sometimes the damage is acute and causes bad problems right away and then permanently.


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## Yooper (Mar 4, 2006)

That was getting long, so I decided to post it before I lost it...

So, can our flashlights cause damage? I think it's safe to say that very few COMMERCIALLY available incandescent or LED flashlights are bright enough to cause damage without deliberate effort or stupidity. If you stare into a SureFire M6 for 10 or 15 minutes you might be able to cause a retinal burn.

HID light sources, however, are much brighter. I'm sure I could cause a retinal burn with my Harbor Freight 30 million candlepower spotlight fairly easily.

Furthermore, some of us here have some crazy bright lights. A USL or a Mag100 would definitely cause some damage with a long enough and close enough exposure. 

I've seen retinal burns from operating microscope lights, which are typicaly 35W 6V or 12V halogen bulbs run at about half brightness, but are focused right on the eye. Usually it takes a looong surgery to cause obvious damage, like 30 minutes or more, but less obvious damage is certainly possible and even probable. Personally I limit how much bright light I use in surgery, often occluding the microscope light between steps.


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## Yooper (Mar 4, 2006)

Why is short wavelength light (blue, purple, UV, like you see with a black light) visually uncomfortable? I'm not entirely sure, but blue light does cause more glare than longer wavelengths, especially within the eye, as it scatters more. 

Is bluer/purpler/UV light more damaging than red/IR? Yes, higher frequency light actually has more energy and more of it is absorbed by tissue in a way that causes damage. The nature of the damage can be different than a simple thermal burn, in that UV energy causes damage directly, without heat, at a molecular level. UV light can actually denature (cook) proteins and can cleave DNA.

Oh, and ophthalmology is spelled with two h's.


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## Lightraven (Mar 4, 2006)

Very interesting, doc! I think your posts should be the definitive word on the subject, but inevitably, they probably won't be. 

Since I have a HF/Costco HID, I'll definitely be careful, although I already knew better than to mess around with it.


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## abvidledUK (Mar 4, 2006)

fixman88 said:


> I remember a while back while I was on the way home I was sitting in the left-turn lane directly opposite a BMW with the brightest headlights I ever saw (in the daytime, no less)! I had to lower my sun visor to keep from being blinded! When I finally turned I glanced over to see if the BMW's brights were on. They weren't.



Headlights reflecting and focussing sunlight ?


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## markdi (Mar 4, 2006)

I guess it depends on how fast your pupil reacts vs intensity and the wavelengths involved.

I would never want to look into my 50 watt phillips dl50 powered hid thor - 5300 bulb lumens

I gave my mom a 10 mcp thor with a 35watt phillips dl35 bulb - 3600 bulb lumens.

she thinks it is really funny to beam me with it as I am walking up her driveway.


the sun - on a nice day reflecting off stainless or a mirror 
must have a lot more energy content than my hid's


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## Icebreak (Mar 4, 2006)

Yooper -

My ophthomologist started using a different tool a few years ago. You know the "puff test" I guess to check pressure? Well he's got this deal that replaces that test. It's a light coming from an optic that looks blue, a bit to the royal side. Well he dials that optic in slowly until it makes contact with the lens. It doesn't hurt, just rattles me a little because I don't want anything near, much less touching my eyes.

What is that device and what kind of light is it using?


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## Yooper (Mar 4, 2006)

Icebreak said:


> Yooper -
> 
> My ophthomologist started using a different tool a few years ago. You know the "puff test" I guess to check pressure? Well he's got this deal that replaces that test. It's a light coming from an optic that looks blue, a bit to the royal side. Well he dials that optic in slowly until it makes contact with the lens. It doesn't hurt, just rattles me a little because I don't want anything near, much less touching my eyes.
> 
> What is that device and what kind of light is it using?



1. ophthalmologist

2. it's the cornea, not the lens

3. It's not new, it's very old, but it's better. The airpuff tonometers are inaccurate. You will find them in places like Walmart Optical because they are automatic and require very little training to use, so you can hire any typical Walmart employee to operate them. He is using a Goldmann applanation tonometer. The blue light is cobalt blue and it is dim and harmless. The device works by measuring how much force it requires to flatten the cornea over a certain area. The tip of the device is a split prism that allows the user to visualize the meniscus of the tear film and tell when the cornea is flattened. The cobalt blue light causes fluorescein dye to glow green. He put a drop of fluorescein in with some topical anesthetic to numb the corneal surface before he did the measurement.


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## Flakey (Mar 4, 2006)

michiganstud said:


> I'm not a regular here, but I just have to say ..... why would you WANT to look into your light? I don't get it.



Cops are usually sprayed with pepper spray before they go out spraying people, also this is often the case with tazers. i dont know about you guys, but from time to time i have shined my lights in my friends eyes just for the hell of it. but before ever doing this i give myself a blast from the light at an arms legnth. If im going to do it to someone else i like to know what exactly im doing that to them. that being said, i probably wont do this with my mag100 when it gets finished =)


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## Icebreak (Mar 5, 2006)

Yooper -

*oph·thal·mol·o·gist* (




f



th



l-m



l






-j



st, -th



l-,



p



-)

Got it. My apologies.

Thank you for the information. My previous Google searches were netting nothing. The Goldmann applanation tonometer is even more interesting now that I have a good explanation of it's purpose and how it works.


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## atm (Mar 5, 2006)

Yooper, thank you for the information, very interesting!

Andrew


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## JimmyB (Mar 5, 2006)

Wow Yooper, thanks for taking the time to post some excellent information. I've saved it locally for my own use and will re-read it later. Oh, and I saw the other h in ophthalmology and actually thought you had made a typo. Ha!

JimmyB


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## LuxLuthor (Mar 5, 2006)

Yooper, thanks for all that. Really an excellent source of information. I'm still looking around for why Blacklights causes photophobia type of pain. I could spend all day on this website: http://science.howstuffworks.com/big.htm

I did find these somewhat related links there: 


Maybe it's partly a form of low light eye strain or not the frequency the cones need to visualize properly?

Why it takes a while for your "night vision" to start working.

This site has lots of good info...including 1/2 way down "Dangers of Defective HID Lamps" which XeRay will love reading! I think the answer is in the latter part of this link, related to Black Light emitting both Blue/Violet visible light and some UV-A light maybe resulting in the minor irritation of cornea.


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## Yooper (Mar 5, 2006)

Icebreak said:


> Yooper -
> 
> *oph·thal·mol·o·gist* (
> 
> ...



No worries. It's a common mis-spelling and that's why I bother to correct it.

Oh, and it's "its", not "it's" in your sentence.


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## Yooper (Mar 5, 2006)

LuxLuthor said:


> [*]This site has lots of good info...including 1/2 way down "Dangers of Defective HID Lamps" which XeRay will love reading! I think the answer is in the latter part of this link, related to Black Light emitting both Blue/Violet visible light and some UV-A light maybe resulting in the minor irritation of cornea.
> [/list]



That is a pretty good site. See figure 8 for an illustration of what I was talking about with tissue absorption. Blacklights put out a lot of blue and violet visible light and a bright light source of this color simply looks "glary" to us and is uncomfortable. No corneal irritation is going on; this would be perceived as foreign body sensation, not photophobia, and doesn't happen that quickly. There is probably alot of scatter as the light traverses the cornea, for more glare.


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## Icebreak (Mar 5, 2006)

Yooper said:


> No worries. It's a common mis-spelling and that's why I bother to correct it.
> 
> Oh, and it's "its", not "it's" in your sentence.



That's true and I try to get it right most of the time however...

The neuter possessive was *his*. The masculine possessive was also *his*. This could cause some confusion. It was up to the reader to decide the difference.

The nueter possessive became *it's* and was *it's* for over 200 years. That did cause some confusion because the contraction for _it is_ used to be *'tis* then changed to *it's*. _It's not it's fault._ It was up to the reader to decide the difference.

*Its *then became the prominent neuter possessive. Yet, this makes no logical sense as most other possessives use an apostrophy and noun contractions for _noun_/_is_ also use an apostrophy. _Icebreak's going to submit Icebreak's view_. 

Yes, *its* is correct but without a strong logical backbone it may too be destined for failure as a word in the next 100/300 years.

Just my bit of verbiage or verbage on the subject dependent, of course, on one's point of view.


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## Yooper (Mar 5, 2006)

Icebreak said:


> That's true and I try to get it right most of the time however...
> 
> The neuter possessive was *his*. The masculine possessive was also *his*. This could cause some confusion. It was up to the reader to decide the difference.
> 
> ...



I didn't know the history. Good info, thanks! I have a copy of "Eats Shoots and Leaves" that I need to get around to reading...


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## Icebreak (Mar 5, 2006)

Yooper -

Etymology can be fun but I find light and optics fascinate me more than about anything.

Apparently you are the only ophthalmologist I've ever dialoged with. I looked up both of the eye doctors I've had and they are optometrists.

I've had some great interactions with both of them. The first one was bent on getting me into no lines. I told him I didn't want an object on my head that would dictate movement. I didn't want to be doing a Stevie Wonder impression. A friend bought me these jewelry-like Armani frames. Sure enough, when I started using them I was rocking my head back and forth to read a computer screen. In the next visit I did the imitation for him and he cracked up. "Ah yes, I see what you mean." He then designed a pair for computer monitor viewing.

Then he designed a third pair for looking at stars. Yep. Stars. I asked him if I would ever be able to see stars again. I explained that with or without glasses, stars appeared to be tiny comets with little tails. I'm not sure what he did but two weeks later I picked up a third pair. I tried them that night and by golly he had those stars dialed in. No charge. He told me he had never been asked that question before and it inspired him.

Here's my optical quiver:

1.) Contacts. Don't wear them very often.

2.) Armani no lines. Back ups that stay home.

3.) Single prescription computer glasses for use with contacts. Take them off to go to meetings etc. Purposely geeky/vogue looking square plastic frames. Made by Verge.

4.) Big bifocals for serious programming sessions looking back and forth between screens, books and notes. No vanity.

5.) Driving/fishing bifocals. Had to be aggressive with the optician to get these the way I wanted them. The bottom prescription is almost all the way across the lens and exists in a little less than 1/3 of the total area. Polarized, amber Easy Clips. My eyes love these.

6.) Ralph Lauren no-line, no frames. Probably my favorites. The optician got everything lined up the way I wanted. The are very light and leave no marks even if I wear them 24 hrs. straight.

I'm serious about my glasses and contacts. "How come you have so many glasses?", I'm sometimes asked. They are the interface between my brain and the world. When I go into an area and see folks with their heads tilted back and rocking or slumped forward peeking over their frames I try to convey to them that proper eye wear will solve their headaches and neck soreness.

It just amazes me that some folks don't want to invest more than 75 bucks on a pair of glasses and then improperly clean them only when they are smudged up enough to be really noticeable.


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## chiphead (Mar 5, 2006)

UV can hurt your eyes just from the reflectant, file this one under lessons learned.

chiphead


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## Ultrastick (Mar 5, 2006)

I've just retired from 34 years of working with blind and visually impaired people. One of my clients, a middle aged lady, told me that when she was young she thought it was healthy to look at the sun, which she did for various periods of time. The eye report revealed evidence of retinal scarring and burns. At the time I saw her she had very little vision left and now knew the error of her ways. Fortunately, humans are the only living creatures we have to tell not to look at the sun. Maybe it's unfortunate. 

As for myself, my belief and opinion, I think that looking into bright lights, whether flashlights, car headlights, bright reflections, or what have you--is a debit on the ledger of our individual vision. Human eyes are naturally drawn to a bright light, so it takes effort to avoid it. As yet, and perhaps the doctor can enlighten us on this, there have been no specific causes found for macular degeneration. This is a disease where the center of vision kind of "burns out", leaving only peripheral vision. I know that during the last years I was working, macular degeneration cases seemed to be exploding. Perhaps bright lights are related to this disease. One of our workers said she noticed a number of her macular degeneration cases were avid readers. These persons would be exposed to bright reading lights and reflections over a period of time. 

Finally, I believe the doctor in his email with the diagram of the eye, in the paragraph beginning "Adding..." --I believe it would be the pupil dilating rather than constricting with sunglasses. 

I hope he posts some more. Good information!

U


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## Yooper (Mar 5, 2006)

Ultrastick said:


> ...As yet, and perhaps the doctor can enlighten us on this, there have been no specific causes found for macular degeneration. .
> 
> Finally, I believe the doctor in his email with the diagram of the eye, in the paragraph beginning "Adding..." --I believe it would be the pupil dilating rather than constricting with sunglasses.



Indeed. That was an embarrassing mistake - corrected, thanks.

There is very weak circumstantial evidence that lifelong bright light exposure is a risk factor for ARMD, but this will be difficult to confirm with real science. I recommend to ALL of my patients that they wear good quality sunglasses as often as possible, as UV light exposure is likely the worst culprit and the most commonly encountered and brightest UV source is the sun.

During WWII sailors discovered that if they stared at the sun with only one eye long enough to cause damage, they could get sent home. In 1944 in the Pacific Theater there was an epidemic of unilateral "foveomacular retinitis" among submariners, and it took the Navy a loong time to discover that these cases were all malingerers. The poor ophthalmologists who were writing research papers on this new, strange epidemic kind of just faded back into the woodwork...


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## Planterz (Mar 6, 2006)

tron3 said:


> Q: What did the Zen Buddist say to the hot dog vendor?
> A: Make me one....<touches finger tips and bows head> ...with everything.
> :laughing:


You deserve a punch in the teeth for that one.


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## Handlobraesing (Mar 6, 2006)

Yooper said:


> That is a pretty good site. See figure 8 for an illustration of what I was talking about with tissue absorption. *Blacklights put out a lot of blue and violet visible light* and a bright light source of this color simply looks "glary" to us and is uncomfortable. No corneal irritation is going on; this would be perceived as foreign body sensation, not photophobia, and doesn't happen that quickly. There is probably alot of scatter as the light traverses the cornea, for more glare.



It does not, unless your definition of "a lot" is different from mine. 
http://unblinkingeye.com/Articles/Light/UVC2/SylvaniaBLB.jpg


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## LuxLuthor (Mar 6, 2006)

I assumed he meant blue & violet ranges of the spectrum, rather than red/green/yellow, which they do output...as well as some UV-A.


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## tron3 (Mar 7, 2006)

Planterz said:


> You deserve a punch in the teeth for that one.


 
Who will do that? A skinny peanut like you? "With weak girly arms." -Bart Simpson

Wait until my next poll. It is likely to have a "let's get him" option.


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## dougmccoy (Mar 7, 2006)

I'm not an opthalmologist, I'm only a humble paramedic. However, I have occular hypertension (a precursor to glaucoma) and I have to, as part of my job specification, have retinal photographs done at six monthly intervals. The process involves anaesthetic eye drops to dilate the pupils and then having a flash camera take pictures of your retina. If anyone is worried about the power of most flashlights then let me tell you that the camera flash involved in this procedure is hellish bright! The problem is that the operator can't always get the image they need on the first take. Consequently it can be three or more shots to get the desired image. Because your pupils are dilated the effect is like having to sit looking at the Sun. Once the process is finished it can sometimes take as long as ten minutes to regain normal vision. The blurred vision as a result of the eye drops takes up to a further two hours to resolve. I've been having this procedure done for well over four to five years now and I also have normal visual checks to determine any visual loss. At the moment my eyesight is still ok and there doesn't appear to be any long term effects from the retinal photography.

Accordingly I would say that unintentional exposure to bright lights whilst uncomfortable isn't normally harmful. However, as with everything, moderation and commonsense must prevail. If you don't have a need to have bright lights shone in your eyes why allow it?

Doug


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## Brangdon (Mar 11, 2006)

Yooper said:


> Just use common sense. If it hurts, don't do it. :ironic:


As I understand it, the converse isn't true. The retina doesn't have pain receptors, so you can be damaging your eye without realising it. This can happen when people stare at a solar eclipse. They must realise the sun is bright, but as it doesn't actually hurt, they keep doing it.


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## hquan (Mar 20, 2006)

Yooper -

Is the retinal damage caused by the light energy creating free radicals? If so - do you know if there is any clinical evidence that eating antioxidants reduce the amount of eye damage?

Also - when people have cataract surgery - do the synthetic lens have the same absorbance in the non visible spectrum as the natural lens?


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## cy (Mar 21, 2006)

wow... what excellent info in this thread!


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## easilyled (Mar 21, 2006)

I think the question is far from stupid. It should concern all of us.
What I find particularly pertinent is that led lighting is a relatively
new technology and I wonder whether the effect of peering into leds
(including luxeons) is even known about sufficiently by the experts.

When I bought my first non-luxeon led torches, there was an instruction
on the packaging warning about class-2 type radiation, which made
me wonder.

Obviously luxeons are still much more intense than non-luxeon leds,
and (has been said before) they emit blue light which has a phosphor
over it to create a white tint.

So does this mean that it can be potentially damaging to stare into a luxeon?

I'd say it probably does until any studies on this subject rule it out.


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