# Power measurement



## badhorsey (Jul 5, 2005)

I know this has been discussed before, but I searched and couldn't find it...

What's the procedure for determining output from a greenie using a green LED?

If some kind soul can point me towards the linkie, I'll delete the post. Thanks!


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## Draco_Americanus (Jul 5, 2005)

http://www.phalkin.com/sbk/PowerMeter.htm


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## LaserFreak (Jul 5, 2005)

That's a helpful link..

Moderators...can we make this a sticky?


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## The_LED_Museum (Jul 5, 2005)

You know, that might not be a bad idea at all. /ubbthreads/images/graemlins/thumbsup.gif
Other moderators/administrators, if you feel this is the incorrect decision, please feel free to unsticky it.


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## DaFiend (Jul 5, 2005)

Yeah, SBK's site is pretty informative. The stickys good, but no doubt there are the people that just come in, not bother reading and try to find info themselves before asking. E.G. " HELP WITH POT MOD PLEASE......" If i see another potmod thread, i'm gonna






The actual inventor of the LED method was nasquadah (and a few others i believe) over at www.greenlaserforum.tk . So...... Credit to him/them, its not acknowledged that often.


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## Kiessling (Jul 6, 2005)

Now that this is a sticky, please try to keep this thread as informative as possible to be worth reading. Maybe it would be a good idea just to mention the different methods, links and possibilities of power measurement and do the discussion elsewhere if it would take too much place? Just a thought ...
bernhard


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## Naquadah (Aug 1, 2005)

Hi! /ubbthreads/images/graemlins/grin.gif
Here is a thread where you can get more information
http://usuarios.lycos.es/naqua/modules.php?name=Forums&file=viewtopic&t=132
And this is the thread in which LzrLight and I invented the method of measuring it.
http://usuarios.lycos.es/naqua/modules.php?name=Forums&file=viewtopic&t=10


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## badhorsey (Aug 16, 2005)

I'm aware that some people have achieved good results with solar cells. Can anyone expand on this - is there a particular type of cell that you need to use, or could you just scavenge one from a handy pocket calculator?


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## The_LED_Museum (Aug 16, 2005)

[ QUOTE ]
*badhorsey said:*
I'm aware that some people have achieved good results with solar cells. Can anyone expand on this - is there a particular type of cell that you need to use, or could you just scavenge one from a handy pocket calculator? 

[/ QUOTE ]
You need a "satellite grade" monocrystalline solar cell, not the kind you find in an old pocket calculator.
These cells have a matte (not shiny) finish to them, and may have several silver lines on top to collect the charge. Aim your laser at any of the spaces between the lines.

Here is the exact procedure for obtaining a power reading from a solar cell (paraphrased from one of my web pages):

To measure laser power, use a monocrystalline silicon solar cell, connected to a DMM on the 40mA or 400mA scale. Shoot the laser at the solar cell, observe the DMM, and note its highest reading (waving the laser around on the solar cell).
Then apply the following mathematical formula:

*(current in milliamps as shown on meter)*1239.7/532/0.97*

The value obtained after the mathematical formula is applied is the laser's output power in milliwatts.
Change the "532" in the above formula to the laser wavelength you're measuring; ie. 473, 593.5, 640, etc.
The formula shown above is for a green (532nm) laser.

It is not known how the solar cell will respond to wavelengths outside the visible spectrum (400nm to 700nm), so in my opinion, this is not a viable method for measuring the power output of an ultraviolet or infrared laser.


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## badhorsey (Aug 17, 2005)

Fantastic stuff! Thanks for that.


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## bertik (Sep 12, 2005)

Check out this link for info on using green LEDs as power sensors.


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## gatekeeper (Jan 6, 2006)

Does anybody know where you can get a cheap mutimeter that can be used for the power test? I have a couple of fluke meters but they're not that sensitive.


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## Chiel (Jan 14, 2006)

I bought a laser power meter at http://stores.ebay.de/Otti-s-Qualitatsprodukte

This is a cheap M-830B multimeter (http://s00106801.shop.auctionweb.info/product_info.php?cPath=28&products_id=AW661955) modified with a silicium solar cell, filter glas and some electronic components. Works very well ! :thumbsup:


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## figaro (Mar 27, 2006)

bertik said:


> Check out this link for info on using green LEDs as power sensors.


... And I could test and confirm the scattering of green LEDS : that's why the figure 2.8 uA / mW is ... a fantasy among much others. Its web-repetirion is not confirmation !!!
Then I attempted something with a LUXMETER :
I used it with the x10 milky cover on the probe and then I read E(lux).
Then I know my laser emits energy corresponding to 10 * E (lux) as if it would be equally spread on the useful part of the probe (the 10 factor is for attenuation of the white milky screen).
This white screen has 40 mm *effective *diameter, ie a 1257 sq.mm area.
* lumens = lux * area* (in square-meters !)
* watts =* lumens / 684 at yellow-peak but *lumens / 600* for green.
mWatts = lumens / .6 for green or ... mW = lumens * 1.67
So *P(mW) = 10 * E (lux) * 1257 * .000001 * 1.67*
Final : *P(mW) = E(lux) * .02*
In my case, the modded greenie gives 490 lux => a bit less than 10 mW.
*Some *of the green leds agree... A lot of them were very optimistic !!! Others were pessimistic... (from 4 to 20 mW).

Last but not least trick : Once you admit the LED meter has only *relative *value, you'll see *much more confortable to aim* at a LDR (photoresistor) for tuning purpose !!!
I'm searching for a calibration method for LDRs ... ??? ...


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## figaro (Mar 29, 2006)

gatekeeper said:


> Does anybody know where you can get a cheap mutimeter that can be used for the power test? I have a couple of fluke meters but they're not that sensitive.


I went on experiences and studies about LDR (photoresistors) : they're *ideal for relative measure* (as tuning tool) because *facility to aim at*.
But to use them as precise sensor, they need some tricky calculation and, worst, figures vary with each real sample.
So, for absolute measuring, I shift on photodiods, and choosed the very available, well known cheap model, the name is *BPW34*, costs less than two bucks (1.5€ here) ,is very sensitive (for those guys who have cheap meters) and rather constant from one batch to another : the *magic number is around 225 uA/mW *for 532 nm* : 2.25 mA for 10 mW.
*They offer *comfortable area to aim* at (7 sq.mm) and more ... so you'll get a free pretty good *luxmeter : 1uA / 50 lux, *except it is not corrected for spectral response (IR reponse).
I'd be very interested to check the repoductibility of my results.


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## figaro (Mar 29, 2006)

figaro said:


> I[...], the name is *BPW34*, costs less [...].


Post Scriptum
CAUTION : *Avoid *BPW34*F* or BPW34*FS* ... or BPW34*B etc.* !These final letters indicate an *added fiter* to *limit the spectral sensitivity* to IR or blue...and then Bye bye the 532 nm and the luxmeter!!!


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## figaro (Mar 29, 2006)

figaro said:


> Post Scriptum
> CAUTION : *Avoid *BPW34*F* or BPW34*FS* ... or BPW34*B etc.* !These final letters indicate an *added fiter* to *limit the spectral sensitivity* to IR or blue...and then Bye bye the 532 nm and the luxmeter!!!


PS for the PS... Sorry Bpw34*B* are convenient !


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## pixar (May 3, 2006)

Hi,

I have a high-brightness led + red laser torch - I wondered if a red led can be used in the same manner green leds are used to check power level? I assume the red laser is between 1-5 mw but it would be nice to know if the same trick works. Reading various threads I see a red led mentioned when checking a green laser (??) but I may have missed where it clarifies a red led can be used to check a red laser (albeit with no w/l conversion).

I've finally received my 100mw green pen but unlike the sales images showing <500mw on the labels, mine shows <50mw - but the seller says he checked them before shipping. Still, when my protective glasses arrive I will use the green led method to check it and see (and black tape, but without protection I am cautious).

btw - pointing a powerful green pen laser at close range onto an led - how come reflected energy does the laser no harm?


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## FlashlightPhreak (May 29, 2006)

Pixar,

Let us know what you think of the green laser once you test it.

Thanks


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## pixar (May 29, 2006)

I believe I posted some of my experiences of the greenie elsewhere - but here's an update.

It does say <500mw not <50 - my label has the '0's very close together. It came from a seller in Italy, who currently has many more of them on sale on ebay - they all go for approx £140-160. So, not a steal but ok if they are what they claim.

I am not convinced it's 100mw, but close. From 8-10 inches I get a painful sting on my hand in about 3 seconds. I can melt and burn through black tape (under some weight) from about 10-12 inches in <30 seconds, but it varies, and I can pop ballons from 4-8 feet in many seconds - again, it varies (no black balloons to hand, so varying colours). The green-led method gives varying results, but a few days ago I got a 230-240ua reading. So, 80mw+. It looks exactly like the nexus lasers - and you can see good pictures of it on the ebay ads.

I have yet to do the infamous pot mod. I am worried about damaging it's looks or ruining the rubber button, and damaging the laser in terms of mode change, and whether it's maxed out already - the ad claimed unmodified - yeah, right


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## nerdtoy (May 31, 2006)

Go to your local University and ask them to check your output using a IR filter in front the laser power meter window/head. Measuring IR is a common and big mistake and give false readings. you need to read just the green and any university will measure it for you with out a problem.


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## MikeAusC (Aug 19, 2010)

Draco_Americanus said:


> http://www.phalkin.com/sbk/PowerMeter.htm


 
This link does not work.


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## bshanahan14rulz (Aug 19, 2010)

It was linked more than 5 years ago. 

There are a few hobby-grade power meters available. Or you could take it to the local uni to get it metered.


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