Welcome to Laser Pointer Forums! If you are looking for a laser you may want to check out the Laser Company Top Sites List. The link will open in a new window for your convenience.

Colorful 2018, Colorful Laser Power Meter
 Laser Pointers Incredible! Semi-Accurate Results from Free LPM?!?!
 User Name Remember Me? Password

#### Menu

LPF Laser Pointer Company Database (link opens new window)

05-16-2011, 07:45 AM #1
 Class 3B Laser Join Date: Jan 2011 Location: Davis, CA Posts: 3,828 Rep Power: 228
Wolfman29
Class 3B Laser

Join Date: Jan 2011
Location: Davis, CA
Posts: 3,828
Rep Power: 228
Incredible! Semi-Accurate Results from Free LPM?!?!

Hey everyone. I may have just made an incredible discovery that will change the world of LPMs as we know it for hobbyists....

So I have been fiddling around with this solar cell, trying to make a decent (within 10-20% error, just for qualitative uses) LPM.

After a bunch of trial and error, I got some semblance of results...!

So first things first: I have this crappy solar panel from a long time ago, measuring in at something like 70cm^2.

Using that, I took out my solar panel outside (with a DMM attached) at highest light and measured the output current and voltage. Now, it's "common knowledge" that the sun outputs roughly 1000W/m^2 of land at highest light. So, using that and the voltage/amperage measurements, I worked out my solar-panel's efficiency to be roughly 7.8%: That is, if it was one square meter in size, it would be putting out roughly 78W of energy (at 70cm^2, it should be outputting 7W of energy, but it was only outputting slightly more than half a watt).

So that was the first step.

The next step was finding some curves that will show me how a typical solar panel reacts to different wavelengths of light. Here is what I used: What type of light cause a solar cell to work?

I tried both curves, and it seems like the second one is more accurate for my solar panel. I will get to that later.

So, I unfocused my lasers wide enough so that they covered the most area of the solar panel without losing too much energy by not hitting the panel and measured output *current*, because solar panels are current sources, not voltage sources.

My results for my three lasers were as follows:

200mW 532nm Rayfoss laser: 6mA
381m*A* LOC: 9mA
~900mA 445: 15mA

Now, there is a clear difference here, if only qualitative: the higher the power the laser, the more amperage it is producing. But how do we make this into a quantitative device?

Here's what I figured out: that second graph? It shows how much amps per watt an ideal solar panel would produce for each wavelength.

So, I did some estimating and got something like this:
660nm: .46A/W
445nm: .2A/W
532nm: .35A/W

Now, I tried it first with the first graph, but my results were so far off, and there was no reason the other one couldn't be more accurate for my panel, so I am trusting the other one is more accurate.

Anyway, what I did next was take into account the calculated efficiency of my solar panel.

I divided the found amperages by the efficiency percent to get "ideal" currents produced by panel.

So, here are those results:
Rayfoss 200mW 532: 77mA or so.
LOC: 115mA or so.
445: Roughly 192mA.

The next step was using these currents and the ratios found in the graphs for each wavelength to determine the wattage of my lasers. I divided this current by the decimal given in the graph, and the result would be the power in watts.

So, here are the final results!
Rayfoss 200mW 532: 219mW!
LOC (set at 380mA): 250mW!
445 (set at 900mA): 961mW!

How damn accurate do those seem?

It may just be a coincidence, but that is just far too unlikely... anyone else agree? Have I just stumbled upon a fantasticly cheap way to semi-quantitatively measure lasers?!

05-16-2011, 09:04 AM #2
 Class 4 Laser Join Date: May 2009 Location: West central Oregon Posts: 5,462 Rep Power: 26216
Flaminpyro
Class 4 Laser

Join Date: May 2009
Location: West central Oregon
Posts: 5,462
Rep Power: 26216
Re: Incredible! Semi-Accurate Results from Free LPM?!?!

The 445 sounds good...
The LOC can sounds ok to low...
maby the cells work beter for the 405 range ?
__________________
White Fusion Time Machine 445
473nm LRS-0473-KFM-00150-10 158.5mW Lab style
laser used in the making of the latest TRON movie

CNI PGL-III-C-589 125mW
520 in a SH-032
Viasho 532nm 500mW
CNI pen 532nm 84mW
The Violet Pip Squeek 45mW

_____________________________________
LOOKING FOR A HOST WITH PERFECT HEAT SINKING
order your C-88 Cu kit today !

Last edited by Flaminpyro; 05-16-2011 at 09:06 AM.

05-16-2011, 09:07 AM #3
 Class 3B Laser Join Date: Jan 2011 Location: Davis, CA Posts: 3,828 Rep Power: 228
Wolfman29
Class 3B Laser

Join Date: Jan 2011
Location: Davis, CA
Posts: 3,828
Rep Power: 228
Re: Incredible! Semi-Accurate Results from Free LPM?!?!

Meh. I am not using a high-efficiency lens, just your normal Aixiz. And I have heard that at 420mA, 250mW is decent for an LOC? Maybe that's just wrong?

Everything seems right though :O Anyway, I figure these figures are within 10% of accurate, because of the estimations done. Once I get another laser diode, I will do some more tests.

05-16-2011, 12:56 PM #4
 ٩(̾●̮̮̃̾•̃̾)۶ __̴ı̴̴̡& Join Date: Jan 2008 Location: Montréal, Canada Posts: 3,588 Rep Power: 1955
rangedunits
٩(̾●̮̮̃̾•̃̾)۶ __̴ı̴̴̡&

Join Date: Jan 2008
Location: Montréal, Canada
Posts: 3,588
Rep Power: 1955
Re: Incredible! Semi-Accurate Results from Free LPM?!?!

Get jerry to investigate on this one.
__________________
CRH-

05-16-2011, 01:45 PM #5
 Class 4 Laser Join Date: Aug 2007 Location: Netherlands Posts: 7,623 Rep Power: 210024
Benm
Class 4 Laser

Join Date: Aug 2007
Location: Netherlands
Posts: 7,623
Rep Power: 210024
Re: Incredible! Semi-Accurate Results from Free LPM?!?!

I suppose its possible to get some results with a solar panel, although having to exand the beam to cover the entire thing is not very practical.

Another downside is that you have to convert the reading depending on each wavelength, and have to determine the conversion factor with lasers of known power for each wavelength.

The question that remains is, however, linearity: Does 200 mW of 532 actually produce 2 times the current 100 mW does? Or is this curve not linear at all? If this is somewhat linear you could use it to compare lasers to eachother, and perhaps also see what any modifications/upgrades actually do for performance.

05-16-2011, 01:59 PM #6
 Class 3R Laser Join Date: Feb 2009 Location: Michigan Posts: 1,859 Rep Power: 203
Lotus_Darkrose
Class 3R Laser

Join Date: Feb 2009
Location: Michigan
Posts: 1,859
Rep Power: 203
Re: Incredible! Semi-Accurate Results from Free LPM?!?!

Even if you do find out that for example: 100mw is half the value of 200mw of a certain color, you still need an actual lpm to test it against.

Don't get me wrong, I find this experiment neat, and if you can even get within 10 percent of accurate results it would be pretty nifty.
__________________
<+vk2fro> mines to operate off two SLA batteries
<+GBD> SLAs? whimp
<+GBD> get a 240V variac and some multiplier :P
<+GBD> then you can have some *real* fun
<+vk2fro> on camping trips where do you expect me to plug that in? a gum tree?

05-16-2011, 03:07 PM #7
 Class 4 Laser Join Date: Oct 2007 Location: Oregon, USA Posts: 5,478 Rep Power: 18104
Bionic-Badger
Class 4 Laser

Join Date: Oct 2007
Location: Oregon, USA
Posts: 5,478
Rep Power: 18104
Re: Incredible! Semi-Accurate Results from Free LPM?!?!

Really, any light/power sensor can be made into a useful LPM--if calibrated to a known source. The calibration is the bulk of what you're paying for when you get a LPM. Even the use of a thermopile over a photodiode is mostly just to avoid needing to apply a wavelength absorption constant. So it's great that you have a relatively accurate solar panel LPM, but the same thing can be applied to any light or power sensor.

05-16-2011, 04:52 PM #8
 Class 4 Laser Join Date: Sep 2007 Location: Wisconsin Posts: 9,292 Rep Power: 199036
Cyparagon
Class 4 Laser

Join Date: Sep 2007
Location: Wisconsin
Posts: 9,292
Rep Power: 199036
Re: Incredible! Semi-Accurate Results from Free LPM?!?!

1000W/m² is a VERY rough estimate. It depends on way too many other variables to be considered a constant.
__________________
A problem well stated is a problem half solved.

Last edited by Cyparagon; 05-16-2011 at 04:52 PM.

05-16-2011, 05:36 PM #9
 Class 4 Laser Join Date: May 2009 Location: Lost somewhere in the EU mess ;) Posts: 5,416 Rep Power: 1478
HIMNL9
Class 4 Laser

Join Date: May 2009
Location: Lost somewhere in the EU mess ;)
Posts: 5,416
Rep Power: 1478
Re: Incredible! Semi-Accurate Results from Free LPM?!?!

Get a small piece of solar panel (say, 1x1 cm or similar), and close it with a tube (for take away side illumination), and ou can get some better results (always remember to not focus your beam to burn, otherwise you can destroy the cell)

Also, yes, they give some decent repetitive results, not as professional cells (and you have to get a response curve from manufacturer, for have a conversion chart), but still enough for some researches ..... remember that also the first "professional" photometers / exposimeters for photography was made with solar cells (in fact, some of them was just a solar cell, a microamperometer and a trimmer ), and they was precise enough, for the time
__________________
High Impulse Multipath Neutron Laser (mark 9 ) (LOL)
Dare mo mita koto no nai, kaze, kumo, suna, umi ..... Kokoro no hate no doko ka eien ga kagayaku.

05-16-2011, 06:28 PM #10
 Banned Join Date: Jul 2009 Location: NYC Posts: 3,403 Rep Power: 0
mfo
Banned

Join Date: Jul 2009
Location: NYC
Posts: 3,403
Rep Power: 0
Re: Incredible! Semi-Accurate Results from Free LPM?!?!

tl;dr

05-16-2011, 06:37 PM #11
 Class 3B Laser Join Date: Dec 2009 Posts: 3,175 Rep Power: 3651
BShanahan14rulz
Class 3B Laser

Join Date: Dec 2009
Posts: 3,175
Rep Power: 3651
Re: Incredible! Semi-Accurate Results from Free LPM?!?!

Shhh, don't teach the proles logic and math, what's wrong with you!

05-16-2011, 07:11 PM #12
 Class 3B Laser Join Date: Jan 2011 Location: Davis, CA Posts: 3,828 Rep Power: 228
Wolfman29
Class 3B Laser

Join Date: Jan 2011
Location: Davis, CA
Posts: 3,828
Rep Power: 228
Re: Incredible! Semi-Accurate Results from Free LPM?!?!

Haha. The great thing about this is that I only need to do math... no calibration necessary, because it's just numbers and nothing that's not exact (for within 10% accuracy, anyway). Now I just need to actually get these lasers tested to see if I was in the ballpark.

EDIT:

@Ben and Lotus:
Yes, there is linearity, or at least there should be, based simply on the theory behind solar panels. For a given efficiency, a certain number of photons knocks out a single electron. Therefore, with more photons, more electrons are knocked out of place. Once I get another red diode or something, I will try it out, but I am fairly certain that this is how it would work.

Last edited by Wolfman29; 05-16-2011 at 07:13 PM.

05-17-2011, 12:53 AM #13
 Class 3B Laser Join Date: Jul 2007 Location: Allentown, PA Posts: 3,626 Rep Power: 44935
MarioMaster
Class 3B Laser

Join Date: Jul 2007
Location: Allentown, PA
Posts: 3,626
Rep Power: 44935
Re: Incredible! Semi-Accurate Results from Free LPM?!?!

Good proof of concept and a sound project - as others have said calibration is mainly what you're paying for in an LPM. People have used LEDs in the past to measure lasers. It's not that hard to make a TEC based thermal laser sensor.
__________________
ILT 5500KR krypton only air cooled ion 100mW 647.1nm | ILT 5500AR argon only air cooled ion >300mW multiline
Omnichrome 643 air cooled Ar/Kr ion 10mW 676.4nm 647.1nm 568.2nm 488nm 476.2nm (high hours)
Spectra Physics 127 >30mW 632.8nm HeNe | Uniphase 1.5mW 543.5nm GreeNe
Coherent Innova 90 argon ion water cooled ??W (got plasma, alignment in progress)
Coherent 60W 830nm water cooled diode brick | Shenhui Laser 40W 10600nm water cooled CO2

(9:03:50 PM) Picasso: the best guys i saw ever at burning man was two dudes dressed as all green army men shooting pants at naked guys

05-17-2011, 01:06 AM #14
 Class 3B Laser Join Date: Jan 2011 Location: Davis, CA Posts: 3,828 Rep Power: 228
Wolfman29
Class 3B Laser

Join Date: Jan 2011
Location: Davis, CA
Posts: 3,828
Rep Power: 228
Re: Incredible! Semi-Accurate Results from Free LPM?!?!

Yeah. I am glad this sort of worked, I just need to make sure these measurements are accurate soon, and then I need to do a prediction test, where I twist a pot and not check the current, then measure the output, then estimate the amperage going through the thing. That should be sound evidence that this works. I may eventually streamline this and start producing photodiode LPMs, calibrated of course... but how would I measure wavelength? Hmm.

EDIT:

Or I could just make a basic one that has different buttons for common wavelengths and then calculate it from there.

Last edited by Wolfman29; 05-17-2011 at 01:12 AM.

05-17-2011, 02:05 AM #15
 Class 4 Laser Join Date: Sep 2008 Location: Quebec, Canada Posts: 16,823 Rep Power: 960027
lasersbee
Class 4 Laser

Join Date: Sep 2008
Location: Quebec, Canada
Posts: 16,823
Rep Power: 960027
Re: Incredible! Semi-Accurate Results from Free LPM?!?!

Quote:
 Originally Posted by Wolfman29 Yeah. I am glad this sort of worked, I just need to make sure these measurements are accurate soon, and then I need to do a prediction test, where I twist a pot and not check the current, then measure the output, then estimate the amperage going through the thing. That should be sound evidence that this works. I may eventually streamline this and start producing photodiode LPMs, calibrated of course... but how would I measure wavelength? Hmm. EDIT: Or I could just make a basic one that has different buttons for common wavelengths and then calculate it from there.
Quote:
 The great thing about this is that I only need to do math... no calibration necessary
I gotta disagree with that.... you WILL need a way of
calibrating no matter what...

You measure wavelengths with a spectrometer...

Like MM said.... have you tried the DIY LED LPM...
LEDs are cheap....

BTW... the optical response curve that you linked to
in the instructables is generic and not necessarily the
same curve as the Solar cell that you are using...

The Link I gave you for a good quality optical sensor
has a data sheet and response curve for that exact
optical sensor (no guessing) that also has a much more
linear curve...

Four years ago we also thought that an optical sensor
was the way to go...
Good luck with your tests...

Jerry
__________________

J.BAUER Electronics Home Page

LaserBee Laser Power Meter Products meet your needs
at affordable Prices:
See them all here on LPF

LaserBee Power Meter products ALWAYS in Stock
and ready to ship

Also available on eBay:Check availability here..

Subsidary: Pharma Electronic Solutions

This banner is available to and can be copied/used FREE by any LaserBee owner

Last edited by lasersbee; 05-17-2011 at 02:09 AM. Reason: spelling errors

05-17-2011, 02:17 AM #16
 Class 3B Laser Join Date: Jan 2011 Location: Davis, CA Posts: 3,828 Rep Power: 228
Wolfman29
Class 3B Laser

Join Date: Jan 2011
Location: Davis, CA
Posts: 3,828
Rep Power: 228
Re: Incredible! Semi-Accurate Results from Free LPM?!?!

My solar cell is a generic solar cell. Like I said, it's not accurate, but it's consistent and, my guess is, within 10% of actual power. If I wanted something to give me accuracy to within a tenth of a milliwatt I would buy a Laserbee, but that's not what I am looking for - I am looking for something that can tell me if it's over or underspec, and a way to tell which of two different color lasers is more powerful.

And regarding the cheap solar cell you linked me to - yes, it's true, it is pretty cheap, but the point of this project was to make an LPM with decent accuracy for free, essentially, or with things I can get at RadioShack for cheap. If I bought that solar cell, why not I just buy the TEC and be done with it? The reason I have done this is because I don't have \$50+shipping to spend on gear right now. :P

By the way, I appreciate all the feedback.

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

Privacy Policy | Advertising Disclaimer | Terms of Use

All times are GMT. The time now is 03:34 AM.

 -- DarkShadows V5 -- Responsive LPF -2562016 -- Default Style Contact Us - Laser Pointers - Archive - Top

Powered by: vBulletin
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.
Search Engine Friendly URLs by vBSEO
Privacy Policy | Advertising Disclaimer | Terms of Use
Copyright (C) 2017 Laser Pointer Forums, LLC