LEDs and eye safety

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Sure. 

I don\'t have a part number in front of me, but some of the LASER
diodes must be.

Certainly. They have thousands (or is it millions?) of times the power density of LEDs.

Incidentally, you *can* see an 850 nm VCSEL laser!

John

Ah, the Long Dong Silver of URLs.

Best regards, Spehro Pefhany

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"it\'s the network..."                          "The Journey is the reward"
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How are white leds quantified with regard to eye safety standards?

60825 does not appear applicable as it stands - is there some other applicable standard?

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I read in sci.electronics.design that R.Lewis wrote (in ) about 'LEDs and eye safety', on Sun, 2 Oct 2005:

In what way is it not applicable?

No, 60825 is meant to be THE one, AFAIK. But there are many parts and amendments. If you go to the public part of the IEC web site, at:

there is quite a bit of information available if you click on each standard number and read the resulting page. For some of the standards (but not IEC 60825-1 for some reason), there is an extensive preview available free of charge.

I would have expected that the diffuse emission from the phosphor of a white LED would not be anywhere near as hazardous as the intense emission from a monochrome LED.

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Regards, John Woodgate, OOO - Own Opinions Only.
If everything has been designed, a god designed evolution by natural selection.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

I read in sci.electronics.design that John Larkin wrote (in ) about 'LEDs and eye safety', on Sun, 2 Oct 2005:

IEC TC76 thinks so, and since they write the standard....

Seriously, if you have a narrow-angle bright LED and put it up close to your eye, but no so close that the image isn't focused, there could be a problem. So you have to be able to prove that there ISN'T a problem with that there LED on your product.

When first introduced, the requirements for LEDs were (either really or apparently) very stringent - the same as for lasers. Since then, there has been a lot of review and explanation. You can see the long list of amendments, revisions and explanatory documents on the web page whose sesquipedalian URL I posted.

--
Regards, John Woodgate, OOO - Own Opinions Only.
If everything has been designed, a god designed evolution by natural selection.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

Floccinaucinihilipilifaction to you Sir !

Graham

sesquipedalian

Word of the Day for Monday October 25, 1999

sesquipedalian \\ses-kwi-pi-DAYL-yun\\, adjective:

1. Given to the overuse of long words; "sesquipedalian orators"
2. (Of words) long and ponderous; having many syllables; as, "sesquipedalian technical terms"

--sesquipedalian, noun: A very long word (a foot and a half long)

llanfairpwllgwyngyllgogerychwyrndrobwllllantysiliogogogoch

martin

Search From Wikipedia, the free encyclopedia. You searched for "Floccinaucinihilipilifaction " [Index] Results 1-1 of 1

*

Relevancy: 0.0% - -

hmmmmmmm. +-3dB maybe, or -1 Boki

martin

The concern I've heard is about ultraviolet LED's, which have a tail of emission that's just barely visible. The concern is that someone will look into/focus on the faint purple glow directly not knowing that there's a lot more power in the UV which they cannot see.

But that seems quite orthogonal to Mr Lewis's concern about white LED's and regulatory standards. I would naively believe that white phosphors would be the most benign.

Tim.

I read in sci.electronics.design that martin griffith wrote (in ) about 'LEDs and eye safety', on Mon, 3 Oct 2005:

Surprising; this sort of trivia usually gets posted to anywhere that will accept it. I don't suppose the Master Wickis deleted it.

Try the alternative 'Floccipaucinihilipilifaction'.

Both mean 'the act of estimating as worthless'. Definite connection to 'Boki' there. (;-)

But the chemical name of any protein is far longer than any normal word. Of course, no-one uses them.

--
Regards, John Woodgate, OOO - Own Opinions Only.
If everything has been designed, a god designed evolution by natural selection.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

Hmm. Real world. The sun has at .5 degree diameter a power density of 1Kw/m^2. Call it 25mw into a semi-dilated pupil. The eye survives this just fine, if you don't try to stare at the sun.

If the LED has a 10 degree beam, and all of it goes into the eye, you need 5W of light, to equal the brightness of the sun. (The illuminated area of the retina is far higher - but over the short term the difference between a .5mm illuminated spot and a 5mm one won't be big.)

I'd say that 1W sources are probably safe - unless extrordinary efforts are made to make them eye harmfull.

We had some green ultra brights that had a warning on them about damaging eyes. They were incredulibly bright! Pat

What you are thinking about, is the 'blink reflex', or 'aversion reflex'. This is the reason why safety levels for IR/UV lasers are set lower than fot the visible light lasers, where the instinct to blink away, is considered to provide extra safety. This is the difference between Class-1, and Class-2 laser standards. You might look at some of the laser standards, and see where the power levels are for these classes. Try:

Which has a nice little calculator, allowing you to try different light frequencies and see how the classes change.

Best Wishes

Briefly, anyway ;-))

There seems to be a blooper here:

"The analysis of the actual worst-case scenario of eye damage by exposure to an LED product can be complex and in some circumstances the most hazardous viewing position may be some distance from the source. This is the case with traffic-light LED arrays. When viewed close up, the radiation from only one LED is imaged in the eye, whereas from further away the radiation from all of the LEDs is imaged (see figure 1)."

Since the LEDs are not a collimated source, 1/r^2 applies, so at a distance the eye will receive a much smaller proportion of the total radiant power. So his statement is quite incorrect.

--
Good day!

________________________________________
Christopher R. Carlen
Principal Laser&Electronics Technologist
Sandia National Laboratories CA USA
crcarleRemoveThis@BOGUSsandia.gov
NOTE, delete texts: "RemoveThis" and
"BOGUS" from email address to reply.

In message , Pat Ford writes

There's also a certain marketing spin on eyesight damage warnings. If you tell someone that an LED can damage your eyes then you think "Cool! It must be really bright."

What they don't mention is that in order to damage your eyes the LED has to be loaded into an air rifle and fired at close range.

--
Clive Mitchell
http:/www.bigclive.com

So, in other words, it's not that LEDs can cause eye damage - only that they can be *too* bright. Just like any other light source/system. Makes sense to legislate just for LEDs instead of requiring a maximum permissible intensity or luminance dependent on the application. Luckily, automotive applications (as the article mentions) already have these limitations in place. The requirements are also there for traffic signals now - unfortunately, not when the systems were first implemented

- and they're not limited to just LEDs.

--
Douglas Cummins
Calcoast - ITL

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Dirk

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