The damage an intense light source, such as a LED, does when viewed without diffusion comes from the cornea focusing the light onto a tiny point on the retina and thus causing burns. Think four year old kid, a magnifying glass and ants.
Increased light sensitivity in lighter colored eyes comes from light "leaking" through the iris, and although unpleasant, this light is diffuse and as such it is not burning the retina.
Since the damaging focused light enters through the transparent pupil, which is transparent in both cases, and not the iris I would think that varying iris pigmentation is an irrelevant factor.
For this reason I doubt that darker irises protects against an intense light source damaging the retina, but I'm not an ophthalmologist. I'd still be cautious of looking directly at an undiffused LED, or giving a light with one to my kids, even if I/they had brown eyes.
And the EDIT: it is not the same case as skin has no irises, no retinas, no pupils and no lenses.
Of course I'd be careful giving kids bright lights. Even if im 10 years away from having one of my own. I wouldn't be giving any of my bright LEDs to any young kids without proper supervision.
Depends on the power of the light, for example if you look at the sun, damage can be instant. Though you may not notice until the later years of your life.
It depends on the distance between the LED and eye, if the eye looks directly at it or not, how fast the eyes reflexes and pupil response are, ambient light and a lot of other variables. Short answer is, it varies. It can be virtually instant, but it can also take a lot longer time. The eye damage may also not be obvious at first since the brain has a tendency of masking small vision losses.
An XM-L has a lower luminance that an XP-E, so they are "safer" than those.
I have never heard of instant permanent retina injuries from looking into the sun; takes quite some staring to become injured. It's much less dangerous than a 1mW laser beam.
Looking at the sun is relatively safe for shorter periods of time, assuming that the eyes are not dilated. Children's eyes are more sensitive and one should avoid looking at the sun with dilated eyes.
I was actually searching for info on this. Yes we know it varies but can you just give a specific example and we can extrapolate from there.
Possible scenario is: xml, on high, light held at arms length, 2 year old kid. I don’t think any damage can arise if you are not looking directly at the light. Do you have any links on the subject? Because I didn’t find any.
http://www.cree.com/products/pdf/XLamp_EyeSafety.pdf They do recommend avoiding looking directly at a lit LED, though after reading this statement it appears that I was wrong about LED’s and eye damage. You might still want to be careful with exposure, especially with children.
Sorry for going off-topic. Guess we all like the technical babbling...
I do think you made the right choice, that incan Energizer is just right for a 3-year old, they don't need something blinding, as long as it emits light in the dark and they can hold it in their hands, they'll be happy.
Thanks DrJones, I was looking for those numbers, because I would like a nine year old nephew to help me build a light and was wondering how safe the result would be in his hands. Your number for the sun agrees with Wikipedia. Sources I found indicated that it takes seconds for the sun to do damage, which puts leds well under the threshold for rapid damage like overheating. I have always suspected that the warnings on flashlights were to impress us, not to protect us.
I didn’t see this post until just now, and it took me a while to find the luminance of the sun.
Yesterday I watched two five year olds playing ball with the sun low, and was concerned about the safety to their peripheral vision. I think what saves it must be the motion of the ball and the ineffectiveness of the eye if it stays still. I do suspect, though that many people have holes in their peripheral vision.
Eye color (of the iris) may — I’m guessing — correlate with pigment actually present at the macula — and that may protect the area of the retina that gets damaged.
Note also that while people can’t look directly at the sun because it’s so bright, people can look for a long time at a 1/40th as bright LED, and end up delivering more total high energy photons to the retina.
This stuff isn’t simple and intuition doesn’t always lead to facts.
BIOLOGIC MECHANISMS OF THE PROTECTIVE ROLE OF LUTEIN AND ZEAXANTHIN IN THE EYE
Annual Review of Nutrition
Vol. 23: 171-201 (Volume publication date July 2003)
First published online as a Review in Advance on February 26, 2003
DOI: 10.1146/annurev.nutr.23.011702.073307
(there’s plenty more research, this is just a tidbit I happened on that will lead to more if anyone follows the citations and “cited by” papers on the subject)
The most dangerous wavelengths for long exposure are those infra red and maybe longer that are absorbed in the lens of the eye. The lenses and bones have the least circulation and therefore the least cooling of body tissues. IR damage is called glass blower’s cataracts. Bones can be heated by radio and micro wave length radiation.
As somebody with blue eyes with a splash of yellow around his pupil, I firmly believe that lighter eyes are more sensitive than darker eyes to brightness….
The way I’ve come to understand it is very similar to a black car and a white car sitting in the sunlight. The dark car always gets a little bit hotter than the white car.
Dark colors “absorb” more sunlight while lighter colors “reflect” more light. Having lighter colors around your eyes, the colored part is reflecting more light in to your pupil simply due to the way lighter color items reflect more energy than darker colors. Having the bright yellow around my pupil makes sunlight that my hazel-eyed girlfriend can handle just fine nearly blinding for me!
Remember, when you see the color of something, you’re actually seeing the wavelengths of light that it REFLECTS, while it absorbs all others…White is the combination of all wavelengths and black is the absence of them. A brighter color is reflecting more, and more powerful wavelengths while a darker color is in fact absorbing them.
Then again, I may be totally wrong on this, but I remember reading about it once a couple years ago. It’s also been linked to blue causing (or more being an effect of) raleigh scattering (which explains the age-old question of why the sky is blue).
I bought one of these on sale because I’m a prepper and reviews said that it runs forever.
It is a decent light, dim, and not much as a real flashlight, but plenty for a kid with perfect eyes, and it runs forever on 3aaas, it won’t burn batteries and it is good for blackouts.
