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Old 05-28-2011, 04:03 AM #33
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Default Re: Looking at a 1-1.5 W 445

Quote:
Originally Posted by LASER ZONE View Post
Diffused light will cook your eyes , trust me mine are toast !!
I agree with you when pointing to a wall , i just mean when pointing to sky at night ,,,, ( raise the hand and strength as far as possible :-p )

However , i agree with you , and i don't play 445nm laser without eye protector ...

So for 1st floor , take care ! at least we don't do the same thing like you !


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405nm purple looks like this color . 445nm blue looks like this color .473nm blue looks like this color . 532nm green looks like this color . 650nm red looks like this color . Hope to play other color laser in hand very much . . Good to try Some lasers pointer here,
I just think 5mW is good enough to play .
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Old 05-28-2011, 04:42 AM #34
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Default Re: Looking at a 1-1.5 W 445

Here's a cool video on 8-16W lasers.

No matter what, your eyes react to the energy in mW....and beware of blue light hazard so don't use your actively cooled 405 to bounce laser off the ceiling for general illumination, to put it in an extreme way.

YouTube - ‪Lichtkunst Light Art Mind Blowing 20 Mile Outdoor Laser Beam‬‏
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Old 05-30-2011, 02:23 AM #35
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Default Re: Looking at a 1-1.5 W 445

Quote:
Originally Posted by Tech_Junkie View Post
Glasses do give you some protection against blue light. Most safety glasses, and eye glasses I've tried block a huge amount of 405nm. I dont think it would be too much of a stretch that they may block some of 445nm too.
Very interesting thread, and I have to credit that statement with making me pull out the LPM to have a little testing fun

Anyway, I decided to see how much if any protection is offered by prescription glasses. The glasses in question are polycarbonate plastic, with a scratch resistant coating. Prescription on them is -1.75.

First to get a baseline I metered two lasers, a 445 and a 405. One is 1.1W +/- 5mW the other is 785mW +/- 5mW. The reason I'm putting in the approximation is that I am using averages of three 1 minute LPM tests, conducted over the period of about 30 minutes (as I watch a tv show), so lasers and LPM had a chance to cool off between each test.

So here's the result. The prescription glasses blocked 130mW of 445nm, or approximately ~12%. They also blocked 100mW of 405nm, or about ~13%.

In addition to those tests, I also decided to see how much the LPM would register from a diffuse reflection. For the diffuse surface I used white cardboard.

From 6" using a 1.2W 445nm laser... the LPM registered 2mW. From <1" 18mW. From about 3 inches... about 10mW.

Now none of these tests are exactly scientific... but they do lead me to believe that the diffuse reflection is not exactly as scary as it is sometimes made out to be. That said, personally I don't view the dots of 50mW lasers from closer than 10 feet.

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Old 05-30-2011, 03:20 AM #36
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Default Re: Looking at a 1-1.5 W 445

That’s good info bro. Wow…2mW from 6 inches diffused reflection on white surface seems higher than I originally thought. I mean I have seen some standards saying 1mW would be the safe level and not 5mW. But then those are relying on the blink reflex, not continuous squinting at the dot for 30-60 seconds from 3 feet (probably like 0.2mW or so) or so trying to burn something. Of course not everybody are into burning stuff, but generally speaking that’s pretty high for us “enthusiasts” esp we are talking about logging usage accumulative times in terms of hrs rather than seconds. I guess its still pretty grey area as far as the general population is concerned, some even take care when playing with high powered LEDs/HIDs (I really don’t know why someone would wanna check out the 5mm arc of a 100W HID – there are people who don’t know the dangers who like to do that as the technology looks cool to them), some don’t care even with a Class IV. Still think it is a good idea to err on the side of caution when dealing with the general population.

Anyway, my Transition glasses really can filter quite a fair bit of my 400mW O-Like defocused to say 4 inches. Put a roll of toilet/tissue paper behind it, there is literally no glow. But again may I disclaim never use this as protection, I STRESS that again never rely on that for 405nm protection, its just for info. I’ll try to get a picture tonight.
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Old 05-30-2011, 05:41 AM #37
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Default Re: Looking at a 1-1.5 W 445

Infinite, that's interesting (and I think actually correlates pretty well to my numbers with the diffuse reflection. Now, how big was your LPM's thermal detector? If it was 10mm x 10mm (standard TEC unit size we use here for LPMs), then it certainly absorbed MORE light than our eyes would at that distance because 1) our pupils are smaller and 2) they are constricted, so they would be even smaller.
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Old 05-30-2011, 06:18 AM #38
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Default Re: Looking at a 1-1.5 W 445

@Wolfman29

Actually I'm using the 2.5W USB Laserbee. I measured it just not, but to be sure also did a quick search:

Quote:
The LaserBee 2.5W USB uses a similar size 15mm X 15mm Wafer type Thermopile
sensor as the Alpha but with a newly developed higher temperature coating.
I do agree that the surface area of the sensor is not the same as that of a pupil:

Quote:
When narrow, the diameter is 3 to 5 millimeters. In the dark it will be the same at first, but will approach the maximum distance for a wide pupil 4 to 9 mm.
The reason I stressed that this is not a very accurate experiment is that the sensor is surrounded by fins to dissipate heat... since the diffuse reflection was hitting these black fins, I wouldn't at all be surprised if my numbers are somewhat high.

The biggest issue with figuring out safe viewing distance ultimately comes down to the reflectivity constant of the surface upon which the laser is being directed. Unfortunately there is not simple way that I know of to test for this.

Edit: I think so far you're the only person to translate from latin without meaning to

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Old 05-30-2011, 06:22 AM #39
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Default Re: Looking at a 1-1.5 W 445

Eep. My bad.

But that's exactly what I am saying. Your results were probably a very high upper limit on the amount of light our eyes are seeing from said dots. Mind doing some tests on that at various distances with the 1.1W 445? Like 1m, 2m, etc.?

I'd like to see some of that data.
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Old 05-30-2011, 06:58 AM #40
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Default Re: Looking at a 1-1.5 W 445

LOL, an excuse to play with my lasers... as if I needed one!

Anyway... Just repeated the experiment except this time I wanted to mimic a worse situation. That and the lasers started to burn through the cardboard

So this time for the surface I cut out a 5"x5" piece from a hefty styrofoam plate... It was the shiniest thing that's not really a mirror.. and white that I came across in my apartment. It was between that and a white tupperware lid but I figured this is more reflective.

Laser used was once again the 1.1W, 445nm. Same as for the previous experiments and LPMed again at 1128mW peak, evening out around 1.1W.

No matter what I tried I wasn't able to get a reading at 1' or farther. At most maybe 1mW of power... not sure if that was an anomaly though.

At 6" the maximum reading was 8mW. Average was 5mW.

At 3" the maximum reading was 36mW. Average was 30mW.

Now I do want to also add that I was trying to create a worse case scenario... and as I said above, I think the results were already high.

In this case since the surface was reflective enough that I was able to direct the very diffuse reflection directly at the sensor at both the 6" and 3" distance. I mean I tried to approximate the angle of reflection with the cardboard as well, but I think the results with the styrofoam are much better in that regard.

I really wish I had a better sensor to do more precise experiments.
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Old 05-30-2011, 07:05 AM #41
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Default Re: Looking at a 1-1.5 W 445

It seems I am turning out to be right (how I enjoy that! Haha). Even the most reflective, non-mirror things seem to be nearly harmless at distances greater than a foot, no?

Now, just to make sure everything is right... mind shining the laser into a mirror and then the LPM? If it reads nearly full power, then we know those are fairly accurate, if a bit high, numbers.
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Old 05-30-2011, 07:09 AM #42
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Default Re: Looking at a 1-1.5 W 445

Hmm... I don't have any handheld mirrors around. I'm gonna have to check in my ex GF's crap, I'm sure she has one

Also I wouldn't really say that it is safe past a foot distance... just at power levels where blink reflex should suffice...

What is a safe mW level for continuous exposure to a laser?
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Old 05-30-2011, 07:17 AM #43
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Default Re: Looking at a 1-1.5 W 445

Update... Just tried it the same experiment with a mirror.

FYI it is rather hard to hold steady both a mirror and a laser... anyway, after taping the mirror upright at 12" from the sensor I was able to get some results.

850mW worth of results Which is less than what I expected actually... but it is still more than enough to fry anyone's eyes.
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Old 05-30-2011, 07:26 AM #44
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Default Re: Looking at a 1-1.5 W 445

Yeah. I am referring to the blink reflex as well. If you are shining it around your room and you hit something extraordinarily reflective but not mirror-like (like your piece of styrofoam), then odds are it is not staying in the same place for a long time, and even if it does hit your eye at the "best" angle, you will probably blink....

But at 10 feet, the power would be roughly 100 times less than at one foot, which can be approximated to be 1mW at most.

I found this Wikipedia article: Laser safety - Wikipedia, the free encyclopedia

which has this graphic:
Looking at a 1-1.5 W 445-800px-iec60825_mpe_w_s.png

If I am reading this graphic right, it means that that the most exposure we can sustain for 400-700nm for an extended period of time (~1000 seconds) is something along the lines of 2-3mW/cm^2... that seems awfully high, but that's what it says, no? And because power density would be higher because our pupils (fully opened) are roughly .39cm^2, we should multiply this by the range just determined (2-3mW) to get something like 1mW or so?

Is that right?

EDIT: So that's a proof of concept, at least. It means that your results shouldn't be that far off from actual in the worst of conditions... so have we just disproven a myth that states that diffuse reflections for a 1W 445nm is dangerous (at least from reasonable distances, i.e. >1ft)?

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Old 05-30-2011, 07:40 AM #45
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Default Re: Looking at a 1-1.5 W 445

That's what the chart says... though it does also seem high to me.

Now here's another statement that bothers me:
Quote:
The maximum permissible exposure (MPE) is the highest power or energy density (in W/cm2 or J/cm2) of a light source that is considered safe, i.e. that has a negligible probability for creating damage. It is usually about 10% of the dose that has a 50% chance of creating damage under worst-case conditions.
Really makes me wish we had an ophthalmologist on the forum to question.
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Old 05-30-2011, 07:50 AM #46
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Default Re: Looking at a 1-1.5 W 445

Meh. That statement is fine with me - it just means that, whatever the power is necessary to have a 50% chance of damaging your eyes, has been reduced tenfold, and that is the MPE that is set. It means MPEs are astoundingly low, meaning that even if the MPE "is" .1mW, the power necessary for damage 50% of the time would still be 1mW.
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Old 05-30-2011, 08:19 AM #47
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Default Re: Looking at a 1-1.5 W 445

Ok, seems like at least that "concept" is mathematically/theorectically proven.
That the diffused reflection is safe, but if and only if when relying on blink reflex (0.1s).

I feel we also need to answer the following very important questions, which actually i and most have mentioned earlier anyway :

(1) When we are shining the laser around on the mentioned non-mirrored/safe surfaces, are we somewhat overriding the blink reflex? (0.1s). It seems that the photochemical reactions on the retina is accumulative. Let me raise another example, in the astronomy circle, some lay people suffer from localised blindness (during solar eclipses even without looking through the telescope/binos, and they don't the eclipse shades so just use their hands to shield and squint their eyes).
I am sure quite a few like to focus their lasers indoors to do popping, squint at the dot etc. For eg, is it safe to try to focus the dot at 3m for 20 seconds? You'll have to multiply by 200x (20 seconds over 0.1s blink reflex), something like that.

Most likely we'd need the professionals to see if we missed out anything important. They'd far more "stories" to share. Its the same in your own respective professional fields, in which reality deviates from theory. Aka Murphy's law.

My apologies if i seem skeptical, because in reality I already experienced some loopholes + close calls....simply because in reality it is never a controlled environment as our usage is really for hobby use.
Heck I already had some close calls with my 100mW Nexus a couple of years ago.
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Old 05-30-2011, 08:23 AM #48
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Default Re: Looking at a 1-1.5 W 445

Understandable. However, we aren't necessarily even relying on the blink reflex anymore. Check out that chart that I posted a couple posts ago - it says that it's something like 1mW of power is safe for ~1000s of exposure. But that seems a bit high. Even then, at one foot, we have determined that it is less than or equal to 1mW of power entering the LPM's sensor, which is bigger than the pupil fully dilated, meaning the LPM is absorbing more of the power than the eye would be in the same spot.

So, that means that at distances of 2ft, it could be at the most .25mW, at 5ft, .04mW, and at 10ft, as little as .01mW.

To put that in perspective, looking directly up at the sun at peak height (dangerous, I know) is roughly 3.9mW of power entering your pupil, assuming it was fully dilated.

That won't blind you. May give you some spots for a couple of minutes, but if you look at something with 10% the power for 10 times the amount of time should give less than or equal to the effect as looking at the sun for that long. So looking at something for 2.5 seconds (.25s blink reflex) that is .39mW is as safe as looking at the sun for a quarter of a second. Looking at something with fully dilated pupils (unlikely) for 97.5 seconds that is .01mW of power, therefore, should definitely be more safe (due to repairs, using different cells, time spread of incident light) than looking at the sun for .25s.

EDIT: And... just for curiosity's sake... why does my 1W 445 seem a lot less bright from, say, 5ft than the sun does when my eyes are dilated at the optometrists? It literally burns my eyes to look at the ambient brightness when my eyes are like that... shouldn't the 1W 445 be *a lot* brighter?

Last edited by Wolfman29; 05-30-2011 at 08:35 AM.
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