LED eye damage

Another major factor is the size of the source. The smaller it is the more energy can be focussed by the eye into a given area.

Dirk

On Sun, 21 May 2006 23:24:07 GMT, dalai lamah wrote in Msg.

...which is the reason why your eyelid reflex will protect your eye from damage.

Really, I think a lot of "Don't look directly into this LED flashlight" crap is just marketing hype. Q: What is brighter than a super-bright flashlight? A: A dangerously bright flashlight.

robert

That would be true for point source radiating equally in all directions, no?

Power is not the issue, it's intensity (power / area). Less power covering proportionately less area gives the same intensity. Moving farther away just reduces the area of damage.

What you say is true only at a large enough distance so that the source is imaged to a diffraction-limited spot in your eye. The image area becomes constant, so reducing power by moving farther away does reduce the intensity. That's why it's safe to look at the stars, but not at our own sun.

Mark

The diffraction limit of our eyes puts a lower limit on how small an image can be. And it's a lot larger than an atom :-)

Mark

"This Light is Awesome! It Will Definitely Blind You! ? 3 Million Candlepower / As powerful as it gets!" ...

Colin =^.^=

That's a perceptive question, and it has an answer.

Putting it more simply: Why isn't looking at Sirius or Regulus as harmful as looking at the Sun, merely to a smaller area of the retina?

The answer is that the lens of the eye isn't perfectly sharp. A sharp image of Sirius would indeed have the same surface brightness as an image of the Sun, but it would be submicroscopically small. The best that the lens of the eye can achieve is an image about 0.01 mm in radius, which is much bigger and therefore has much lower surface brightness.

Now, if we had a star 10 times as far away as the Sun, or maybe even 100 times as far away, it would be dangerous to look at. But the nearest stars other than the Sun are more than 60,000 times as far away, if my quick calculation is right.

Exactly. And the eye is usually a good bit worse than diffraction-limited.

I have heard people complaining when they look at my 45 watt LED setup. I try to warn them first.

greg

Heym,Don,have you checked out the River Rock 0.5W white LED flashlights Target sells for $10,that run on two AAA cells? (7 hr claimed) They're pretty nice,IMO.

Thats seems like a good combo and life. I was looking at all the Target lights at Xmas. I bought 3 or so brands. For myself I got a 1W Lumiled powered by 3 AAA. Only 2.5 hrs. Nice metal case, but I'm looking for a nice plastic non conducting case for working around electricity.

greg

plastic non conducting

Just bought an Aurora for about $25, 1.5W, 2xC alkalines. Life about 10hrs. Totally excellent buy. It's very bright and the machined ally case is superb.

Dirk

The damage that leds can cause to the eye is well recognised and is covered by IEC 825 / EN60825 and related. The word 'laser' in the title I suspect leads some to ignore 825 but it is directly concerned with leds - in fact it states that for the word LASER read LED throughout the text but the title has never been ammended.

Several (in fact a remarkaly high percetage) of the classII and above products I have happened across have had no obligatory labelling and warning leaving open the door to litigation and prosecution. There are legally enforceable regulations (in N. America, Europe etc) concerning the application of even quite low power leds in all products because of the problems of possible eye damage in the longer term.

Once, at a trade show, some years ago, one of the exhibitors had a panel of Ultra-Bright LEDs that you could not only see from the other end of the auditorium, but when near it it was actually painful to look at, and I could feel the radiant heat from them on my skin.

I didn't spend much time looking at them, because it _hurt_.

Thanks, Rich

In article , mc wrote: [....]

This isn't really true. As the area gets smaller the power per unit area to cause damage increases.

..or any source once you get far away.

Are you saying that a collimated laser beam obeys the inverse square law? If the beam diameter does bot inc erase appreciably wit the distance why would the power drop off?

A collimated laser beam does not stay collimated forever. Once you're far enough away the beam will start expanding with distance (because of diffraction), and the intensity will obey the inverse square law.

How far away is "far enough away" depends on the wavelength and the starting beam diameter of the collimated beam, and is proportional to D^2 / lambda

Mark

I used a neon laser to make a really straight line on an airfield strip. At 3 kilometers the beam diameter was about

We also discovered that the runway was going up and down more than 2 meters. -( -(