How do you protect your eyesight when playing with LEDs?

Cemoi

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Jan 23, 2008
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529
Location
France
Hello,
I've just tried my very first power LED: a red-orange Lambertian Luxeon I.
I connected it to two NiMH in series, with a variable resistor to control the current. I occasionally watched at the LED to see if its brightness increased when I changed the resistance value. I quickly realized it was too bright to look at, and put on my sunglasses (very good ones which I use for mountaineering) to protect my eyes. Then I kept on playing with the LED, looking at it for a few seconds at a time occasionally. Since I drove it at 70 mA maximum, its brightness was much less than the nominal brightness at 350 mA.

But when I removed my sunglasses and looked at a white wall, I saw a very distinct and intense blue spot in the middle of my field of view. I was first scared as I feared I had damaged my eyesight. Strangely after looking at the white wall for few seconds the blue spot fainted and became less visible, but if I closed my eyes for a few seconds, as soon as I opened them back the blue spot was here, very intense.

Fortunately after 10 minutes or so it started being less bright, and one hour later it is completely gone. Of course I feel quite relieved, but after this clear warning I will be more careful.

What do you guys wear to protect your eyes when experimenting LEDs?
Would the special "sun eclipse" goggles be OK to look directly at a LED?
Or should I put my LED in a vertical paper cylinder so that it lights the ceiling only, and I can not see it directly?
 

mds82

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May 1, 2006
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Location
Connecticut
i have a set of dark red glasses, i dont know where i got them from however - maybe something from a laser pointer? they arent welding glasses or anything, but they definately make a HUGE difference. i can look at a Cree Q5 at 1000ma and be fine ( for a few seconds at least)
 

Oznog

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Joined
Dec 2, 2006
Messages
595
The human eye is already at a logarithmic scale when judging brightness. That is, a source must be 4x brighter for a person to judge it "twice as bright", even when side-by-side with another.

But when faced with blinding light, the judgment is out the window. Could rate it as anything really.

Here's what to do- just throw a sheet of notebook paper over the light (as always, be sure you have adequate heatsinking). That diffuses it quite a bit and attenuates it to something tolerable.

The diffusion has another benefit. Even lambertians have the intensity depend on angle and you probably will not take that into account, looking at it from one angle, bend over to adjust the power supply, look again but you're 20 deg off from your first look and you probably won't realize that. But with the piece of paper, the diffusion makes it easier to judge brightness regardless of angle since it's pretty nondirectional at that point.
 

hank

Flashlight Enthusiast
Joined
Apr 12, 2001
Messages
1,561
Location
Berkeley CA
A quick look with Google found this
http://sci.tech-archive.net/Archive/sci.electronics.design/2006-05/msg03877.html
That's from an expert, most people here will recognize his name.
There's far more in the thread than this bit.

----excerpt----------
...
When it comes to LEDs and LED flashlights, you may end up relying on
power per unit area of emitting surface. For example, a more intense
white "Luxeon" could emit .4 watt from a chip surface magnified to roughly
(my eyeball estuimate) a 1.6 mm square, and that is roughly 16 watts per
square centimeter - which means you hit maximum safe exposure in about 4
seconds if you are close enough for 1/4 milliwatt or more to pass through
your pupil. This is about 1/4 the upper limit of Class II.

However, some time ago a Cree distributor showed me one of their LED in
action, and before lighting it he warned me not to look directly at it. And
he was right, these LED produce a light that you can't stand, even from
several meters.


I hear enough cautions and warnings related to looking into enough
LEDs... I would consider in general high brightness LEDs to be equivalent
to Class II lasers, and laser class II is a wide range of 2500 to 1.
...
 

1 what

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Jul 6, 2007
Messages
617
Location
Australia
I use the good old ceiling bounce or if I'm feeling hi-tech or want more accurate data use this:
rampplustextxo1.jpg

You don't have to use a photodiode panel plus CRO. A simple LDR plus $10.00 multimeter will do.
Look after your eyes....most of us only get one set per lifetime.
 

saabgoblin

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Nov 2, 2007
Messages
725
Location
Far side of crazy.
You could always get a pair of welding goggles, I just tried the two shades that I have, a #5 and a #10. The 5 is for Oxy Acetylene welding/brazing and the 10 is for Arc Welding. The 5 cuts down the brightness and may be helpful with accidental side spill but if you want to look directly into an led, I would go for the #12 or higher but you can barely see through a #12 shade lens so it would be useless IMHO for anything other than playing around and not recommended. I would say a shade 5 or higher would be nice extra protection for accidental side spill but I would never recommend that you look directly into a led with anything less than a shade #12 lens and keep in mind that I am no ophthalmologist so proceed with caution at your own risk. From what I know, eye damage is cumulative so it would be unfortunate to have a great collection of lights and no sight to see them with.

I do know that if you experience a headache after working with leds much like welding, you have probably done some damage and the spots that you mentioned may also be a sign of damage.
 
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VanIsleDSM

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Joined
Oct 16, 2007
Messages
649
Location
Victoria BC, Canada.
A #5 is most likely far more than you would ever need.

The robotic welding machines I work with produce a welding arc 44X the intensity of the sun at high noon on the equator. A #10 or #11 is all that's used. #12 is for extremely hot welding.
 

mickeyjc

Newly Enlightened
Joined
Nov 14, 2008
Messages
3
You better get a LUX METER ... It is pretty cheap from ebay.
Don't look at the high bright source directly with your own eyes, it will damage your eye sight.​
 
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