Oddball LED Light question

[Anti_Candescent]

Is it possible for a LED to produce light harmful to the eye? I know the UV's aren't good on the peepers head-on. Is it possible for a LED of any color (non uv) to be producing light in a dangerous spectrum?...or producing a harmful wavelegenth with its normal output?


Enlighten me please /ubbthreads/images/graemlins/bowdown.gif

 

[tonyb]

Any bright light into your eyeball is not good thats why they tell not to look directly at the sun. I use to look directly into my .5 mW HeNe laser and now have blind spots because of it.
tony.

 

[HarryN]

You might be interested to know that the European's are setting up to classify all solid state lighting (including LEDs)the same as lasers. The concept is based on light concentration, and the potential of looking at the light at some distance with a telescope, etc.

The FDA is now accepting their definition as an alternative, and will likely formally accept it soon. LEDs in the 5 watt class will most likely be rated as class IIIR if I remember correctly.

So the answer is, yes, it appears to be more than just a wavelenght issue.

 

[The_LED_Museum]

The bottom of one of my flashlights has a label that reads:
CALSS 3R LASER PRODUCT
Note the spelling of "Class". It is misspelled on the flashlight this way.
It has a brand new Nichia NCCW022 SMD Power LED in it.

Here's a picture of the underside of this particular flashlight:

 

[PhotonWrangler]

It seems to me that any light that's sufficiently bright enough to cause you to see spots afterwards is causing a certain amount of heating inside your eye, and that can't be good.

 

[Wits' End]

If warning labels become mandatory on lights, will that increase the cost of product liability insurance?
Anyone make plastic bags? /ubbthreads/images/graemlins/smile.gif

 

[gwbaltzell]

Just spots is not an indication of damage. If the spots don't go away, then that's another story. Even the chemicals in our eyes for bright light (color, photopic) vision take a short while to rebuild. Most of the problem is, as Craig states, the small beam. Our eyes don't get enough total light to close our iris down, nor enough to give a pain response so that we would look away. I think even my 1 W white everLED could do some damage.

 

[idleprocess]

The issue with LEDs is that they're often a point-source of light. In the case of even relatively modest 3mm white LEDs, they're an intense point source, which can burn the retinas with enough exposure.

As far as wavelength goes, regular visible-spectrum LEDs generally only emit light in the visible spectrum. Save for a new alternate chemistry for white LEDs that was just released recently (ZnSe?), white LEDs are a blue LED that shines on a phosphor that glows white when energized by blue photons.

The alternate-chemistry white LEDs also only emit light in the visible spectrum (as far as I know).

There has been some development on white LEDs that function similar to florescent lamps (generate UV light that shines on a phosphor that emits white light), but I don't know that there are any of those LEDs in production. UV/phosphor LEDs would probably emit some UV along with whatever visible spectrum they produce.

I'm sure that Craig of the LED Museum can elaborate if necessary.

 

[BB]

There is also this LED Warning Thread which spoke about blue LED's (450nm or shorter) wavelengths causing eye damage too.

-Bill

 

[Anti_Candescent]

Great, you guys really give some good information. Now I have more questions!! /ubbthreads/images/graemlins/smile.gif Could a LED be made to shift wavelegenths? Something that read light conditions and changed the spectrum and level of light?? I'm dreaming here, sorry!

 

[Aten_Imago]

Not sure if LED's can be made to shift wavelengths but it could be possible to design a double dicroic polarization filter that would act like a super gate instead of a clear lens. Bi-color polarizers could be used as a wavelength modulator.

 

[louie]

Luxeon data sheets say, "No UV" at least.

 

[The_LED_Museum]

Older MQW (multiple quantum well) 450nm blue LEDs can be coaxed into emitting a sharp UV spike at 385-390nm by providing high-current, short length pulses to them.
This web page explains how to do it.

There are no other LEDs that can shift wavelengths - not intentionally, anyway.

 

[Anti_Candescent]

Interesing, thanks for all the info guys.

 

[PhotonWrangler]

[ QUOTE ]
BB said:
There is also this LED Warning Thread which spoke about blue LED's (450nm or shorter) wavelengths causing eye damage too.

-Bill

[/ QUOTE ]

Thanks for reminding this of us, Bill. I think that the potential for eye damage from an LEd is going to be affected by several things including it's beamwidth, optical power, wavelength and duty cycle.

Regarding damage from IR LEDs and (low power) lasers, I've read somewhere that IR wavelengths longer than around 900nm are not focused properly on the retina, so the retinal damage threshold from IR might be different from that of visible wavelengths.

In short, if it hurts, don't look at it! /ubbthreads/images/graemlins/grin.gif

 

[PhotonWrangler]

[ QUOTE ]
The_LED_Museum said:
Older MQW (multiple quantum well) 450nm blue LEDs can be coaxed into emitting a sharp UV spike at 385-390nm by providing high-current, short length pulses to them.
This web page explains how to do it.

There are no other LEDs that can shift wavelengths - not intentionally, anyway.

[/ QUOTE ]

I remember that article... thanks for the link to it. It's possible to shift the color of electroluminescent panels slightly by varying the AC drive frequency... I wonder if this is the same mechanism by which that blue LED can be "tuned?"

 

[The_LED_Museum]

I don't believe the same mechanism is responsible for both phenomenon. I could be wrong here, but I don't think so.

 

[PhotonWrangler]

[ QUOTE ]
The_LED_Museum said:
I don't believe the same mechanism is responsible for both phenomenon. I could be wrong here, but I don't think so.

[/ QUOTE ]

Some diode lasers that are used in DWDM networks are tuned thermally. The wavelength of diode lasers does walk around a little bit over temperature, and in some cases this is exploited as a useful characteristic, allowing several LDs to be tuned slightly apart from each other and then combined onto the same F/O strand.

The fixed-wavelength lasers that are used in fiber optics are held at a given temp by a Peltier junction TEC cooler so they'll stay in the center of their window. I think this is one of the reasons why the greenie pointers change their brightness over temperature drift - the pump diode is drifting in wavelength. So I'm guessing that the physics behind the blue-to-UV shift in the blue LEDs is related to the wavelength drift in laser diodes.

Thinking about it more, I suspect that this is a different mechanism from the EL panels, so you're probably right, Craig.

 

[NikolaTesla]

My L6 HURTS my eyes and I would NOT recommend looking directly in it for more than .1 seconds (A Flash)

NikolaTesla
/ubbthreads/images/graemlins/mecry.gif
An Arc is the Spark that takes away the Dark--
http://www.tjtech.org/gallery/NikolaTesla/Nikola_lights2_001

 

[carbonsparky]

I have seen a demonstration where LEDs were dipped in liquid nitrogen. This would cause a visible color change. It was a long time ago and I don't remember what colors were used and what colors resulted, but it was changing one base color to another if I remember right.