Is LED harmful to the eyes (if one looks directly into it)?

[Tachion]

Wow… that is quite a few parameters to consider:

• Output "strength" from the light source.
• Size of the light source (LED die and reflector).
• Distance from the light source to the eyes.
• How dilated your pupils are, i.e. ambient lighting when the light is pointed at the eyes
• Exposure time.
• Which spectrum the light is in might have an affect as well.

What I'm about to write is anything but scientific and probably not what you asked for but a while back I had an experience I'd like to share. I tried looking directly into a Fenix P2D premium 100 (rebel). I wanted to check how effective a flashlight might be if I ever needed to temporarily blind a perpetrator of some sort. Luckily, I did not try it on turbo, instead I believe I selected medium (50 lumen according to the manufacturer) and I guesstimate that I looked into the light for no more than one second at a distance of 25-30 centimeters. The size of the LED in a P2D rebel looks pretty tiny… perhaps the smallest of any of the lights I have. I tried this in the basement of my apartment house. No daylight, but the ceiling lamps (60W) where on so I don't think my pupils where more than halfway dilated.

• Output: 50 lumen
• Size: Reflector – 16 mm / LED < 2 mm (pretty small)
• Distance: 25-30 centimeters
• Pupils: Not more than halfway dilated.
• Exposure time: Less than a second
• Spectrum: Not a clue. But I'm sure someone can tell me.

It was decidedly uncomfortable and the result was in fact a bit scary. My entire center field of vision was completely "blanked" for perhaps 30 seconds! I could literally not se my hand in front of me! x2 After that it took perhaps 10-15 minutes for the "spots" to wear of my vision. My eyes seem fine today, but as someone pointed out, you never know how things will progress with time.


With children I guess you can't really control the Distance, Exposure time or how dilated the pupils might be. What you can control is how powerful and concentrated the light is. So the idea that a few posts here already suggest, to use a low power light with a diffuser on, seems the safest way to go. I think document tape should provide some diffusion. It might be a good idea to get it on the light as seamlessly as possible and without the children watching.

But I also believe that there is no substitute for knowledge. I will definitely make sure my kids (if or when I have a few) know they should not look straight in to any kind of bright light and be careful of where they aim flashlights. Until I can tell they understand and respect the power of modern flashlights, I'd stick with giving them low power lights with diffusers on.

 

[MetalZone]

I agree, a small 5mm LED should not be a problem for a child's eyes (IMO, but I'm not a doctor). The latest high power LEDs are a different story, but I think most people quickly learn not to stare directly into them.

I recall reading on wikipedia (always taken with a grain of salt of course) recently that current high power LEDs may represent a "blue light hazard", sounds possible to me and they do reference a source (actually theres a second source as well) both of which I have yet to read over.

Taken from here:
"There is increasing concern that blue LEDs and white LEDs are now capable of exceeding safe limits of the so-called blue-light hazard as defined in eye safety specifications such as ANSI/IESNA RP-27.1-05: Recommended Practice for Photobiological Safety for Lamp and Lamp Systems.[31][32] "

Interesting. In fact, a little alarming to me. The research does seem to have some merit.

 

[hank]

An Arc AAA spectrum:
http://ledmuseum.candlepower.us/eleventh/arcd-1.gif

White LEDs all have the blue spike (that's the primary light emitted) and the broad band emitted by the phosphor after it absorbs some of the blue photons and emits most of that energy as a range of somewhat less energetic photons).

(This is why over-driven "white" LEDs get that blue-to-violet color, they're running too hot, and the hotter something is the higher energy (bluer) photons).

What we see is the average our eyes make -- that's "color temperature" and that's why you can't just rely on "warm white" as a description -- if it's a LED or a fluorescent it will still be light with a large spike of blue in it.

That scary story (thank you for the caution) -- here's your spectrum (much the same)

http://ledmuseum.candlepower.us/eighth/p2d1.gif
Spectrographic analysis of the LED in the Fenix P2D CE Flashlight.

Typical of "white" LEDs.

Blue photons carry enough energy to knock electrons off of atoms, producing ionized radicals.

Amber and red photons do not carry enough energy to knock electrons off of atoms.

http://209.85.173.104/search?q=cach...t=clnk&cd=4&gl=us&lr=lang_en&client=firefox-a

There's your mechanism -- why the blind spot lasted a while (it might have been safer to turn off all the room lights til you recovered!) --- good reason for concern. Your next optometry exam, if they dilate your eyes, should look at your retina and tell you if they see anything cautionary. Blind spots are easy to ignore, but ought to be noticeable in exams.

"... When light hits a photoreceptor, the cell bleaches and becomes useless until it has recovered through a metabolic process called the "visual cycle." 30 31 Absorption of blue light, however, has been shown to cause a reversal of the process in rodent models. The cell becomes unbleached and responsive again to light before it is ready. This greatly increases the potential for oxidative damage....."
http://www.mdsupport.org/library/hazard.html#blue

One reason little kids may be at more risk -- the lens of the human eye becomes more yellow over time (probably as blue light damage accumulates from ordinary daylight exposure). That blocks out blue light, as the yellow tint increases. (It may also be why older people need more light to stay alert -- it's the blue light range that keeps the brain awake!).

--
Searches for "blue light" and "hazard" will find prior posts I've made with other cites; this is not a new concern. At least one thread got moved to the 'Cafe' as inappropriate.

Check Google Scholar and Medline for current research; this is very new science and changes fast.

"Be careful reading medical books. You might die of a mis-print." -- Mark Twain

 

[2xTrinity]

(This is why over-driven "white" LEDs get that blue-to-violet color, they're running too hot, and the hotter something is the higher energy (bluer) photons).

Although that's true in general, I don't think that's the reason why overdriven LEDs run "angry blue". It's not that the wavelength emitted by the die is getting shorter as much that beyond a certain temperature, the phosphor becomes less and less efficient, so less of the 450nm blue light is converted to other wavelengths. The net appearance becomes more blue.

What we see is the average our eyes make -- that's "color temperature" and that's why you can't just rely on "warm white" as a description -- if it's a LED or a fluorescent it will still be light with a large spike of blue in it.

Mercury-based sources, like HID or fluorescent, I suspect are worse -- if you look at the mercury lines, there are large emission at 405 and 430 nanometers. LEDs emit primarily at 450nm. Not only are the shorter "lines" going to be more damaging than 450 (shorter wavelength = more energetic photons). The eyes are also FAR less sensitive there, so they will be perceived as "dimmer" than a 450nm led of the same power.

I still believe color temp is going to be a reliable guide of blue light exposure though, at least comparing similar light sources to one another. If you were to compare a 450nm blue LED, and a 3500k warm white LED both radiating one watt (optical output, not input power), you'd receive orders of magnitude less blue light from the latter -- both because there is less blue light in the output, and because the warm white light will appear far brighter (eyes are most sensitive to yellow/green light), so pupil diameter will be smaller. The same effect should be noticed going from cool white to warm white, as well.

I also suspect that when talking about damage from short wavelength light, point sources are particularly bad. In nature there is a LOT of UV and blue light, but never does it come as a point source -- it is scattered/diffused in the sky. That's why I have no problem with fluorescent blacklights, but am EXTREMELY apprehensive about using UV LEDs.

http://ledmuseum.candlepower.us/eighth/p2d1.gif
Spectrographic analysis of the LED in the Fenix P2D CE Flashlight.

Typical of "white" LEDs.

Blue photons carry enough energy to knock electrons off of atoms, producing ionized radicals.

I'd be interested in seeing specific numbers as to which frequencies are ionizing, and to what extent. Ie is 450nm as bad as 430? Is 470nm still bad? 485? 500?

"... When light hits a photoreceptor, the cell bleaches and becomes useless until it has recovered through a metabolic process called the "visual cycle." 30 31 Absorption of blue light, however, has been shown to cause a reversal of the process in rodent models. The cell becomes unbleached and responsive again to light before it is ready. This greatly increases the potential for oxidative damage....."

Interesting. This would suggest that the mode of damage from blue light is consecutive exposures on the same spot on the retina, which is much more likely when dealing with a point-source.

All this discussion reinforces my decision not to buy any more LEDs until they start to come out in the 3500k color temp range. Not only be a more useful light source lumen for lumen, it would be safer and less glaring to use around others, as well. Leave higher color temp stuff to natural light, and computer monitor backlights -- all of which are inherently diffused

 

[jtr1962]

I also suspect that when talking about damage from short wavelength light, point sources are particularly bad. In nature there is a LOT of UV and blue light, but never does it come as a point source -- it is scattered/diffused in the sky. That's why I have no problem with fluorescent blacklights, but am EXTREMELY apprehensive about using UV LEDs.

I agree 100% here. Fluorescents have always had very spiky spectrums, way more so than most white LEDs in fact, yet this blue light issue has never come up in the over 60 years they've been in use. However, by their nature it is impossible for them to put a very high intensity of light through your pupil. Even putting your eye right up against a T5 tube isn't going to blind you as much as staring into a 5mm superbright white LED from a foot away. Old school T12 tubes were even less intense. You could stare at them for hours if you wanted to with no discomfort. LEDs changed all that by enabling a source with a blue spike to be put into a highly focused package.

Another recommendation here to prevent eye damage in children is to retrofit wide angle LEDs. I'm referring to the top-hat kind which spread the light over 100 to 120°. Peak intensity is reduced from as much as 100 cd to usually under 1 cd. You'll still have the same number of lumens to get around if the same chip is used, but the intensity will be harmless. This lets youngsters enjoy the benefits of white LEDs. Let's face it-you could I suppose give a kid a red LED if you want to play it safe, but it has virtually no "wow" factor, and it will stink in actual flashlight use. More than likely the kid will call it his/her (insert slang term for feces which starts with a "c") light. A wide-angle white is a good compromise between safety and usability.

 

[hank]

> fluorescents
The blue light problem does come up with fluorescents, but much less often (see the mention of using bright white fluorescents for 'winter blues' treatment in the link above -=- something I've done myself for years now).

> wide-angle white is a good compromise
I agree.

I'm using amber/yellow LEDs for kids for camping.
They are awfully hard to find as ordinary flashlight LEDs.
They do work a lot better than the red ones for general illumination.

 

[Tachion]

There's your mechanism -- why the blind spot lasted a while (it might have been safer to turn off all the room lights til you recovered!) --- good reason for concern. Your next optometry exam, if they dilate your eyes, should look at your retina and tell you if they see anything cautionary. Blind spots are easy to ignore, but ought to be noticeable in exams.

Thanks for the advice about turning off all the room lights to let the eyes recover. I'll remember to do that if anything similar ever happens again. I will most certainly never check if a flashlight might be usable as a defensive device by pointing it at my own eyes again. But you never know if you'll get "flashed" by mistake.

In fact I never let anyone try any of my "powerful" flashlights without warning them not to look into it when they turn it on. I also instruct them not to point it at anyone else's eyes when they turn it on (easy to do if the on/off button is placed at an unfamiliar location… "oh… here it is -> ").

As for the optometry exam, I don't regularly do those. So unless they can actually do something that helps, I think I'll give that a miss and pretend my eyes are fine.

(Edit: spelling)

 

[natalia]

Thank you all for your answers! I think, a discharged cell will be a solution for my 2 yo daughter

 

[Yapo]

Thank you all for your answers! I think, a discharged cell will be a solution for my 2 yo daughter

I guess its never too early to be getting into flashlights

 

[yekim]

As usual; a simple question posted here on CPF has devolved into a scientific dissertation.

I have a mess of little kids and they all have been playing with flashlights since they could grasp things. I have not had any issues with them shining them into their own eyes or the like. I believe flashlights are a beneficial learning tool for children as they teach multiple things through their usage.

The main problem I have is that they will leave them on and forgotten in some strange place.....There are probably a $100 worth of lights mixed in with the kid's toys somewhere. Maybe more. Sometimes they leave them on and the drain causes batteries to leak.

There is also the chance that a child can tear the light apart, and this is where I think a light like the Dorcy Metal Gear light stands out because you can really wrench it together and keep a child from tearing it apart, unlike my Super 1 watt that was once found spread through the entire expanse of a bedroom, or my Surefire L2, which gets warm enough to almost cause pain if left on high.

Kids like lights, I like lights.....we have something in common..

One other consideration, I have heard that there is lead used in the manufacture of the rubber button covers of some lights. I do not have a lead test kit or anything, but I did make sure that my kids were not using lights as pacifiers, and in the case of some really cheap lights I just removed the cover.

 

[hank]

> a discharged cell will be a solution for my 2 yo daughter

Beware unscrewable and swallowable parts! (Put a big keyfob or something on the tailcap)

 

[Federal LG]

Yesterday I accidentally flash my Lumapower IncenDio in high mode directly in my eyes. I got a black dot for almost 30 minutes, and a kind of disconfort in the back of my eyeball for a couple hours!












Ok.. it was not accidentally.

 

[hank]

OK. More than you wanted to know.

Remember a few postings back, mention that after a very bright light exposure, the retina is going to get more damage from even dim light, for a while?

I speculated that after you blind yourself temporarily, you could turn ALL the lights off -- til your retinal pigment has time to recover -- to protect against the second type of damage.

Short answer -- yes, if you have blinded yourself, then for a while after that, even low light causes additional death of more cells in the retina (probably because they're already damaged and unprotected until the visual pigment recovers, which takes a while).

Bottom line, my opinion -- tell your eye doctor when you have your next dilated exam.

(Also, don't run with scissors, don't put anything in your ear that's sharper than your elbow, and wash your hands regularly. Common sense -- help make it more common.)


http://www.nature.com/ng/journal/v32/n2/full/ng1002-215.html

--------excerpt------------

... Excessive exposure to visible light damages the vertebrate retina. New work demonstrates that two different pathways, a bright-light pathway and a low-light dependent pathway, mediate light-induced retinal death. ... both pathways are initiated by excessive activation of the photopigment ....
...
We all know that overexposure to light—for example, from directly watching a solar eclipse—can damage the retina. But in the mid 1960s, Noell and colleagues made the surprising observation that visible light "at intensities which are ordinarily encountered" may, at least in some conditions, damage the photoreceptors .... light-induced photoreceptor apoptosis* ....
---------------end excerpt--------
* apoptosis: a genetically determined process of cell self-destruction that is marked by the fragmentation of nuclear DNA , is activated either by the presence of a stimulus or by the removal of a stimulus or suppressing agent, is a normal physiological process eliminating DNA -damaged, ... http://www.photothera.com/glossary.cfm

More: (now, this one is about mice, you know how this stuff works)

"... We focus on apoptosis pathways in our model: light-damage induced by short exposures to bright white light and highlight those essential conditions known so far in the apoptotic death cascade. In our model, the visual pigment rhodopsin is the essential mediator of the initial death signal. The rate of rhodopsin regeneration defines damage threshold ..."
http://linkinghub.elsevier.com/retrieve/pii/S1350946204000710

So --again -- after the initial blinding flash, it takes a while til your visual pigment recovers (to where you can see again) -- and the time involved has a connection to how much additional damage gets done by the less bright light around you.

Or I think that's what they're saying. I don't have the full article.

I better stop here before someone gets the mistaken impression I know what I'm talking about. Just reading aloud with my lips moving here.