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LPM Request (Free diode!)

Insomniac

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Hi all, first post here.

I've got a bit of an odd request I was wondering if someone could fulfil for me.

In my quest for a decent, (reasonably) eye-safe laser for just messing around with, I've gone and bought a cheap 635 5mW diode from eBay and a housing to place it in. However, as we all know eBay sellers can't exactly be trusted to rate the power of their laser components accurately. As I don't have access to a LPM, I'm hesitant to trust that the laser I end up building is going to be safe.

Now, I'm aware there is a system for posting lasers to members with a LPM in order to get them checked. However, given the low cost of the parts in this laser I figure the expense and time delay of shipping my laser to another member really won't be worth it.

Would any member like to volunteer to measure the output of the diode I have bought, if I buy a second diode and have it shipped directly to them? Whoever ends up doing this for me can just keep the diode when they're done, as it's not worth shipping it because it's so cheap.

Ideally I'd like to have a set of measurements at different drive levels, in say 5ma increments from 0-35 ma. That should give me a reasonable indication of whether these diodes are over-spec or not.

The diode is the one listed here:
http://www.ebay.com.au/itm/201064687537?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649
 
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ryansoh3

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Welcome to LPF! :wave:

It depends on what current you want to drive the diode. If you drive it at a low current, you will have a low powered output and thus have an eye-safe (5mW) laser.

If you have a power supply, you can adjust the current to your liking and get a driver to output that current in your laser.

However, I'm sure there are many in Aus who'd be willing to measure and plot the diode's output vs. current. It will need to be in a module and a heatsink. (Maybe not, if it's really rated at 7mW as in the datasheet.)
 

vortish

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there is one other consideration that needs to be mentioned. Not every diode is going to produce the same mw. It should be close but every so often one out performs the rest. you might buy twenty of the same diode that are suppose to be five mw but one might come out at thirty or some thing like that. so this just information for your but do as you will and many LPF members will meter diodes for nothing other than postage good luck
 

Insomniac

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Yeah, I'm aware that I can keep an eye on the current to set an upper bound on the output. I'm not worried about accidentally building a massively powerful laser, as I'll be measuring the drive current when I end up building it.

What I'm concerned about is ending up with a ~15mw laser instead of a 5mw one.


For instance, if it's running at 30 ma, vF of about 2V and an efficiency of ~20%, I'd expect to see around 12mw output. However, this is higher than the eBay datasheet says, so I'm assuming that the efficiency must be worse. Does anyone have a reasonable ballpark efficiency for these cheap diodes?

I've ordered a module to house the diode when I get it. I doubt that I'll need much heatsinking given the very low drive current, but I'll keep an eye on the temperature when I test it.

I figure that anyone with an LPM will have a spare module lying around they can use to test... Alternately, holding the bare diode right up against the detector ought to work fine.

The variance between individual diodes is of slight concern, but I figure they'll probably be close enough that I can be confident in its safety. Even extremely cheap diodes like these were measured to be fairly consistent in power output.
 
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crazyspaz

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Keep in mind, even if you get some freak diode thays doing 20mw at datasheet rated input, that still isnt really dangerous- obviously avoid looking into it, but it wont be blinding if you accidentally catch a reflection off something. You seem like a careful person (good on you for that), so you should be fine if its a little more than 5mW :)
 

Alaskan

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If 5 mw is the limit to be considered safe, why would 20+ mw be safe too?
 

crazyspaz

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Hmm, well let me rephrase what i typed above.

if you catch the reflection, or even the full beam of a 20mw laser, if wont blind you. And, like i said, he seems safe, so its not like he will be staring into the thing.
 

Alaskan

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OK, I understand you, but you were the one bringing up reflections, he wasn't. I think he was talking about in case it was shined into someones eyes but there I am assuming too, he didn't say that either. I'm bringing this up regarding 20 mw in case someone misunderstands you.
 
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RayJay

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I am in Australia, Have an LPM on the way (should be here in a few days as my Ophir got stolen) and have a 5A variable power supply..

And would be happy to measure it for you :yh:
 
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Insomniac

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Ah, excellent. If you PM me your address, I'll order a second diode for testing in the next few days. I'll take a chance on diode variation, for the time being. I appreciate your time!

As for why I don't want a ~20mW laser... It is mainly for the sake of reflections, but also to reduce the risk from direct hits. I sometimes view the beam of my 650nm red from in front of the laser. It looks cool, but opens up the risk of a brief direct hit. Just want it to be low power so that I don't have to think too hard when playing around with it. Plus, I have no need for it to be brighter. If I want to view the beam, I'll buy an overspec eBay greenie and just use it outdoors.

Thanks for all the responses!
 

Insomniac

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Alright, both RayJay and TheLightningStalker have kindly offered to test out these diodes for me. Given the very low price, I've opted to take both up on their offers. This should give some insight into consistency between diodes and ensure that at least one person receives a working diode in a timely manner.
 

Bionic-Badger

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Hmm, well let me rephrase what i typed above.

if you catch the reflection, or even the full beam of a 20mw laser, if wont blind you. And, like i said, he seems safe, so its not like he will be staring into the thing.
FAIL.

Stop spreading harmful disinformation.

You need to get a clue. That 20mW is indeed dangerous, especially a full beam of 20mW can cause eye damage. Even specular reflections (shiny surface reflections) are considered dangerous. In fact, 5mW is only considered "blink-reflex safe" -- not considered "eye safe" in the general case.

Insomniac is right to consider the safety of his eyes and others in the laser he's building, especially since > 5mW will place it in Class 3b land. He should only use the laser for pointing or otherwise if he can ensure that the beam will only hit matte surfaces. Otherwise, the beam can directly reflect into someone's eye with dangerous levels of power.
 

Insomniac

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Bionic-Badger said:
You need to get a clue. That 20mW is indeed dangerous, especially a full beam of 20mW can cause eye damage.
While I would absolutely treat a 20mW beam as being dangerous, it is worth noting that the ANSI MPE values are based on a factor of safety of around 10. So in their studies, it actually must have taken something in the ballpark of 50mW to cause visible, measurable retinal burns from a brief exposure.

Regardless, 20mW is close enough to that number that it should be treated with a great deal of respect. It's just interesting to see how these power limits were initially established.
 

crazyspaz

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FAIL.

Stop spreading harmful disinformation.

You need to get a clue. That 20mW is indeed dangerous, especially a full beam of 20mW can cause eye damage. Even specular reflections (shiny surface reflections) are considered dangerous. In fact, 5mW is only considered "blink-reflex safe" -- not considered "eye safe" in the general case.

Insomniac is right to consider the safety of his eyes and others in the laser he's building, especially since > 5mW will place it in Class 3b land. He should only use the laser for pointing or otherwise if he can ensure that the beam will only hit matte surfaces. Otherwise, the beam can directly reflect into someone's eye with dangerous levels of power.
Jeez, calm down. im not "spreading harmful disinformation". Did I tell people, "Hey, go get a 20mW laser and stare right into it, you will be fine!"? no, i did not. "You need to get a clue"? Really? I said a 20mW laser wont blind you if you catch the reflection or full beam. It wont, it simply wont. If you stare into it like a moron, then maybe. but a flash across the eye will not cook your eye, like a 1000mW 445 will. many years ago, before i was on these forums, i had your typical overspec chinese 532 pen, probably around 50mW. I caught the beam for well over a second, dont remember the circumstances, reflection of some kind. That was visible light AND IR, mind you. my eyes are both completely find, no damage done.

Like I said, I am in no way telling people to go stare into lasers. I was simply saying that even his diode preforms well over 5mW (at 20mW), it wont be some blinding death-to-all-eyes handheld weapon of insanity.

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EDIT: Since i was so grossly misunderstood, and apparently people cant quite read, I was not meaning to imply 20mW is not dangerous at all, ever never ever. I was stating that Insomniac seems to be a safe enough person that, even if the diode is a bit above spec, he will not be in any serious harm. I found an example on LPF alone- link. There are more examples if you do a simple google search. I'm on my phone and don't feel like going through the hassle of linking them. You also have to keep in mind everyones eyes are different, which is maybe why i didnt suffer damage from my incident, but maybe you would have long lasting damage from a 6mw laser (exaggerated circumstances, you understand my point). Again, I was in no way saying "Hey everyone, go stare into 20mW lasers, you will be fine!". Look at your visitor messages, Bionic, the top most post; this could have all been avoided.
 
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Bionic-Badger

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Jeez, calm down. im not "spreading harmful disinformation". Did I tell people, "Hey, go get a 20mW laser and stare right into it, you will be fine!"? no, i did not. "You need to get a clue"? Really? I said a 20mW laser wont blind you if you catch the reflection or full beam. It wont, it simply wont. If you stare into it like a moron, then maybe. but a flash across the eye will not cook your eye, like a 1000mW 445 will. many years ago, before i was on these forums, i had your typical overspec chinese 532 pen, probably around 50mW. I caught the beam for well over a second, dont remember the circumstances, reflection of some kind. That was visible light AND IR, mind you. my eyes are both completely find, no damage done.

Like I said, I am in no way telling people to go stare into lasers. I was simply saying that even his diode preforms well over 5mW (at 20mW), it wont be some blinding death-to-all-eyes handheld weapon of insanity.

DOUBLE FAIL.

It's even worse this time because now you're defending your harmful disinformation. Yes, you are effectively saying that getting hit in the eye by a 20mW laser will not cause damage to the eye.

This isn't about "staring" into lasers. A laser beam above 5mW in visible wavelengths/NIR entering the eye is not eye-safe because it will cause eye damage before your blink reflex kicks in. Your body can't protect itself against, for example, dropping the laser and the beam hitting your eye even for a short moment. A laser of total power > 5mW can be eye safe only if you can guarantee that it will be spread out enough over area or time to have power densities that are safe (like at a laser show). However, you don't get that benefit of the doubt because this is just "a 20mW laser" that in its default configuration does not make any guarantees about power densities -- something you should not assume.

The inability of your blink reflex to protect your eyes is why such lasers are Class 3b, not class 3r/3a (< 5mW). It's the same reason why the FDA forbids lasers with power > 5mW from being called "laser pointers." They are not safe for general use.

So yes, GET. A. CLUE. Stop spreading this false information, or even worse, lies if you continue to knowingly push this false information.

And spare us your anecdotal evidence. It is meaningless in this context. Only the general case matter, which is what these laser safety standards are for.

And yes, I'm going to get all over your case. An ignorant person who provides bad information to others is far more dangerous than someone who is simply ignorant.
 




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