Light Meter....

[ViReN]

Hello All,

I am on a look for a good light meter. I Know "Wavetek Meterman LM631 Digital Light Meter" but if you look here... http://www.testequipmentdepot.com/meterman/light/lm631.htm .... a BIG OUCccccchhh.....

$100 + Shipping (assuming that they willing ship to India) $ 25 - $50 atleast.... ..... I simply cannot afford it. Also, I am not willing to buy any seconds etc.

Need something good and at less $$$ (something similar to cheap DMM that i procured recently) ... Hmm I Know, light meter will not be that cheap & it is not available Locally too /ubbthreads/images/graemlins/frown.gif .... I even went to many PhotoStudios if they have any light meters etc... but /ubbthreads/images/graemlins/frown.gif

Any Guidance.... ?

Thanks in Advance

ViReN

 

[Roy]

Goto your local Radio Shack and ask for a solar power demo kit. I used the solar panel from one of these kits for over a year to measure the battery run time of various flashlights. The solar cell is not calibrated but is useful for relative measurments. Just plug the solar cell into your DMM and measure the mA output of the cell.

 

[andrewwynn]

I have seen very decent looking meters on eBay for $50

-awr

 

[ViReN]

Roy.....

Absolutely Greaaaatttttttttttttttttttttttttttttt

I Live in India, Dont have RadioShack Stores... BUT..... I have an very very easy access to solar pannels.

In fact, I had thought of using it previously, but i was not sure how well it would work....i was wondering about wether the Solar panel has linear current generation... properties

Will it be a Linear type of Cell (panel) Current ? I mean, if we increase light output linearly.. the Current supplied by the solar panel is equaly proportionate (increase in value) ??? ... there should be some kind of limit to this too i guess...

Is there any method / Software where in i can directly measure (Solar panel)current at a preset intervals of time using some sort of Interface to a PC and logs it in to some sort of data file (may even be text based file)? from there i will carry on with the calculations & Plots (Microsoft Excel is such a nice tool)...

Thanks & Regards,
ViReN

 

[Roy]

As to being linear....few things in nature are linear! I seem to remember from my photography days that the lightmeters were not linear.

What you are describing is a recording DMM with a serial computer output. I have a computer program that reads the serial data coming from the DMM.

Do a Google search on lightmeters or recording meters, ets as see what you can find.

 

[ViReN]

Hello Roy,

Thanks for your response. I think I do not need the Computer Connectivity at this moment. It would be just better for me to get hold of a Solar Panel and hook it up to DMM to measure current at regular time intervals for measuring relative Current & plot a graph for the runtime for the circuit...

It will also help me in do some analysis of different type of confiturations etc....

My Whole Hearted Thanks to you Roy. I am thinking of getting a 1/2 watt or may be less solar panel.... what would be appropriate according to you?

ViReN

 

[Roy]

Here's a picture of my origional test set-up.

Here's a close-up of the photocell. Depending on what you are trying to measure, this could either be too big or two small.

Here's a picture of my present test set-up with the Extech Mdl 401021 LightMeter Adapter.

 

[ViReN]

Wowww Roy, Awesome /ubbthreads/images/graemlins/smile.gif

Thats Very very nice of you to put up pictures. It helps a LOT .....

My intention is to check for the duration for which the Transistor based Step Up circuit will work with various cell chemistries & Capacities. It will also give me a relative o/p vs time graph and the nature the circuit works with various LED configurations.

I will be going to an Exibition today, Luckily there is an exibition running on, a couple of exibitors have solar panals & gadgets at display I would be able to get the panal at a lower rates too /ubbthreads/images/graemlins/smile.gif hopefully.

I will be looking for a similar sized solar panal that you have used. Will keep you updated with the things.

I also want to thank you very very much for taking time & efforts to reply to my post that too so fast replies.

Thanks once again
ViReN

 

[ViReN]

OK, I am back from the Exitibion.... The lowest price that they offered was $12 for a 5 Watt Panel.... which is on expensive side... so... my next best bet was search online...

http://store.sundancesolar.com/minsolpan45v.html i found this one.... will it be good enough for my purposes ?

Its cheap... shipping charges also comparitively less....

Thanks in Advance
ViReN

 

[MrAl]

Hi there,

Nice pic's Roy, thanks for posting them.

Viren:
So you're making your own light meter? That's not
a bad idea.

Take care,
Al

 

[Roy]

Viren....the photocell that I used had an active area of about 1 inch by 2 inch....it looks like it was two 1in x 1in cells wired together.

 

[ViReN]

Hmm, I need a light meter to test the batteries & Circuits performance + Runtime + Behaviour.

I am also thinking of using a LDR May be, just to see if that can be used or not ? I m not sure... What do you think ?

Light Dependent resistor could give results ?

-ViReN

 

[MrAl]

Hi viren,

I think you missed my previous post, not that it was
'that' important...but...

The photo cell is used mostly because of it's known
linear response to light. The output is proportional
to input -- pretty much anyway -- if you measure short
circuit output current (not voltage). The only trick
is measuring short circuit current without allowing
any voltage to appear across the cell. This requires
a small resistor to short the cell with, and then the
output is also small but can be read with a digital
meter.
A good resistor value would be 0.010 ohms, but then
the output would be very low, so maybe 0.1 ohms will
be good enough. 1 ohm would be too high for a real
linear output.


Take care,
Al

 

[ViReN]

Hello Roy,

Thanks very much for your reply. I will be searching for something similar sized tomorow.

I also have one more question, do you think that a Light Dependent Resistor will be useful for the purpose ? where in i can measure resistance as a measure for intencity ?

Thanks & Regards,
ViReN

 

[ViReN]

Hello Mr Al,

Sorry that i was in some sort of hurry... Actually I am not building a Light Meter... (though i wish it though)....

Currently, i am thinking of just making a sensor that will tell me about relative light emmitted by the LED's against time.

Is there any kind of circuit that can be used to do a quick n dirty light meter /ubbthreads/images/graemlins/smile.gif

Also, If we are using the PhotoCell.... wont the Shunt of DMM Suffice ?....

For Ultra Low current measurements i have DMM (the cheapo) that can measure as low as 200 MicroAmps Range....

Thanks & Regards,
ViReN

 

[Roy]

Test set in the first picture is complete....photo cell, DMM and computer....nothing else.....other than the X-Y plotting program that came with the logging DMM.

 

[MrAl]

Hello again,

Viren:
Well, you can make a light meter out of anything that
senses light really, if you're willing to calibrate it.

Set up your sensor (whatever it is) and maybe a yardstick
(or other distance measuring device) and start with
an LED maybe 12 inches from the sensor and look at the
output on the meter. You'll have to make sure to
keep the angle of incidence constant too. You can take
it from there using this to calibrate it:

Once calibrated, it would be easy to use just like a
regular light meter except you would have to look
on your scale to determine the true light reading.

For example, say you get the following readings and
determine what the actual reading should be from the
lightmeter shown in the drawing

[meter, actual]
10, 10
30, 20
50, 30
70, 40

Now when you take a reading, you would look up the
measurement on the meter, then use the scaled value
instead....
so say you read '50' on the meter, then you look that
up and you get 30 as the actual level.

It takes a little doing but it's simple once you
get going...

I've found that even those clear glass diodes are pretty
sensitive to light, but dont generate much SC current.
Perhaps a larger resistor and calibration.

Take care,
Al

 

[ViReN]

Hello Mr Al,

Thanks for the valuable information about calibrating & Making the things little bit linear. I was slightly "Offline" from CPF. I have now ordered about 6 - 8 Cells (flexible & Glass) both from http://www.pagermotors.com The shippins was surprisingly LOW ... Just $3 /ubbthreads/images/graemlins/smile.gif and it was cheaper than what would i have got in here India...

Here, they had asked me for something like 20$ for a good panel where as i could get much more for the same cost + Shipping... /ubbthreads/images/graemlins/smile.gif isnt it nice ?

I will be Calibrating the "Light Meter" According to your method. I think, u got solution to Every Problem here /ubbthreads/images/graemlins/smile.gif /ubbthreads/images/graemlins/smile.gif /ubbthreads/images/graemlins/smile.gif

I will be back again on this thread. once i get those Panels.

Its really Worth to mention Special thanks to You & Roy.
This Helps me greatly.

Thanks & Regards,
ViReN