Laser meter with a green LED

[Naquadah]

Hi! i`ve benn testing with a DMM and a green LED in short circuit,and the maximum current measure I obtained was 14,4 microamperes for a green laser pointer <5mW
Does someone know any equation to obtain mW in this way?
Any other measures of your laser could be helpful too
BTW, i hit the led from his head, so the measure was maximum

/ubbthreads/images/graemlins/thumbsup.gif

 

[i7r7]

Hah... I asked this question a while ago in antoher GLP thread, whether or not it's possible to measure a laser without a photodiode. However, it seems that an LED is similar to a photodiode in some ways.

Umm... if someone could use both a professional laser meter and LEDs to measure a range of GLPs, it would be possible to work out a formula.

Damn... I would have never thought of using an LED photoelectric properties to measure a laser. I would like to confirm my measurements that I made with my photodiode. Apparently, my modified 5mW Changchun read 59mW.

Please don't mind my English... I don't know what I'm saying. I've been talking crap.

Jeff

 

[kakcoo]

I don't think that's possible. You won't get the dot i focus if the lightsource is to big.

 

[kakcoo]

 

[Naquadah]

The lightsource is the GLP, im sorry i dont understand what are you trying to say, we are speaking about measuring the power of a green laser with a green Led, which I think its possible because in many ways its like a photodiode.

 

[i7r7]

I am so confused right now... well it is past midnight but I think it would be possible to use an LED to measure the output of a laser. It's all about the photoelectric effect, I actually remember stuff from high school physics. /ubbthreads/images/graemlins/smile.gif

Jeff

 

[disys]

Easy...

1/ Take a green LED of known manufacturer (one that everybody can get their hands on, regardless of the country you live in)

2/ Everybody takes a reading with their GLP (including those who have a calibrated unit or know the power output of their GLP)

3/ We all compare notes and we work out a formula

TADAAA! There you have it. /ubbthreads/images/graemlins/tongue.gif

 

[Naquadah]

mine 20 microamperes (the maximum i achieved to read)

 

[Naquadah]

oh, hehe its rated <5mW

 

[PhotonWrangler]

What if the LED produces a logarithmic (rather than a linear) response to illumination level? Will we still be able to cook up a formula that accounts for this?

wondering,
/ubbthreads/images/graemlins/thinking.gif

 

[disys]

Hell yea!

We'll just plot the results and make a table of values! /ubbthreads/images/graemlins/thinking.gif

something like

10ua = 3mw
20ua = 5mw
30ua = 17mw
40ua = 26mw
50ua = 42mw
55ua = 56mw

And so on....

We don't even have to know anything about the response of the LED.. as long as we all use the same device and it shows some change at various power levels. We'll "standerdize" it's output and plot the result.

Voila!
/ubbthreads/images/graemlins/party.gif

 

[Naquadah]

I don´t understand why the post has been moved... /ubbthreads/images/graemlins/banghead.gif now only a few people will see it and talk about it
/ubbthreads/images/graemlins/thumbsdown.gif for the admins
BTW, the Led i used was something like this one, but on g reen

 

[B@rt]

Ok, one last time... /ubbthreads/images/graemlins/icon6.gif
The thread has been moved because it is about electronics. /ubbthreads/images/graemlins/thinking.gif /ubbthreads/images/graemlins/twakfl.gif

I also think you are wrong in assuming it will get less exposure this way. the electronics forum is very active. /ubbthreads/images/graemlins/wink.gif

A last reminder, please read the Posting Policies, in particular rule #6. If you have an issue with admin, take it to PM or e-mail...

 

[Naquadah]

It´s ok... but I dont think in that way.. Imagine if someone is trying to measure the power of his laser, and he doesnt know how to do it, where will he search? On electronics forum? On homemade lights or modified?
For me, its obviously he will take a look at the Laser forum, and I´m sure that many people will agree with me

 

[B@rt]

Hey, you're allowed to think any way you want, but this site has certain rules wich have to be followed...
It's really a simple rule, if it has to do mainly with electronics, that's where it goes...

A lot of people do understand these rules... If you do not, feel free to open a forum on your own acount. ( I guarantee you that you will have to put up rules as well, and what good are rules when they are not obligatory? /ubbthreads/images/graemlins/wink.gif )

 

[WildRice]

I tried a few different LED's last night. I found that only the old formula green ones kinda worked, I had more LED output by using an older yellow one. but get this, I got some current out from a RS IR LED. This may be the way to go, as these IR LED from radio shack would be easier for everyone to get, well I suppose that RS green LED's would be easy to get at a consistant level to all also.
.02
Jeff

 

[Doug Owen]

Measurement of output *power* is not an easy one to make (one of the reasons Power Meters are so expensive). Even to low precision (a few percent), which would be hard to sell to many more demanding users. It's far more complex than simple light level measures, since power invloves wavelength as a factor.

It is definitely not possible to even estimate output from LED Lasers by input power. It is highly non linear, indeed the first energy in produces no light as 'lasing' hasn't happened yet.

That said, it should be possible to make relative measures and if one of the sources is known (say a well characterized LED of the same color), the ratios should be useful for low precision. You'll have to be very careful to be sure you fully capture the laser beam (reflections will lower the reading) and fully characterize the capture of the reference light (from the LED), neither is trivial.

So those who suggest photodiodes or phototransistors (or even photoresistors) are on the right track.

As far as a low cost commercial unit, I'd suggest you don't hold your breath......

And FWIW, I agree with Bart. If you want technical answers, got to the forum where us Techie types hang out...... And, right or wrong, this is their sandbox, we either play by their rules or play elsewhere, right?

Doug Owen

 

[Naquadah]

Yea, its the "stronger law" /ubbthreads/images/graemlins/wink.gif
BTW, when i measured output from the LED, it had a great variance, so I took the maximum read when the laser was touching the head of the Led.
Wildrice, I think that if using an IR Led, the measure wont be "real" due to the amount of IR output of the laser
Im thinking about creating a forum for green laser lovers /ubbthreads/images/graemlins/smile.gif, it would be great

 

[WildRice]

I have been doing some testing with a sony nightshot camera, and it looks like most of the IR IS blocked by the internal filter. Hey, wanna 'see' what the hazards can look like. Take the IR filter off the laser and shine at a wall and view the emmissions with a camera, one with nightshot will work better. The diode itself with no optics on it, at about 12ft away makes a rectangle about 1'x5' of 808nm, extremely bright, but not visible. ONLY TRY THIS IF YOU UNDERSTAND AND ACKNOWLEDGE THE HAZARDS INVOLVED!!!!!!!!!!!! Once you can see the ratio of visible to invisible light thrown out of one of these things, you can understand the potentional hazards.
Jeff