How to measure runtime

I recently bought a lux meter, but the problem is that it is not datalogging. I'm trying to figure out how to do runtimes without sitting next to the lux meter for hours. Any ideas?

I came to the light... said:

I recently bought a lux meter, but the problem is that it is not datalogging. I'm trying to figure out how to do runtimes without sitting next to the lux meter for hours. Any ideas?

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There are many possibilities, some of them are:

• Buy a logging meter.
• Buy a light sensor and connect it to a datalogger.
• Use a camera as light meter.

W.W.Granger has the Extech light meter with software program and cable to connect the meter to a computer. You choose start time, end time, sample time and number of samples. The results are saved in Excel. You can also choose what types of screen data you want to see during the test or none at all.

Curt

:thumbsup: +1 for the Extech Datalogging Light Meter, Model 401036. Beats checking in every so often and writing down the readings.


C.P.T.

Thanks for the replies.

How might I connect my current lux meter to a datalogger? It does not have any ports.

The datalogging meter referenced is too expensive, especially after having already bought one. And unfortunately I do not own a Canon camera.

Video camera ...

Tape it while your away ...

Or do it the hard way ... Which you dont want to do ...

So do it when you watch TV ... Take the readings at every commercial break .

yeah, I don't think there are that many alternatives.. maybe if you could get a camera timed to take pictures every minute? maybe a webcam?

Thanks for the additional input. It seems like those ideas could work, but would obviously not be ideal. I have a Sony T900... which I don't think can be set to take a picture every minute. TV would screw up the readings, and besides, I actually don't watch TV

The problem with taping it is going through the tape, which I could skip through, but then I'd miss smaller fluctuations. Now, if I could find (or make) a program to save a picture at every point that the video's image changed more than a small amount, it would be pretty straightforward from there, but with that much effort I'm starting to think it would be better to just buy another lux meter, this time datalogging.

So, what's the cheapest datalogging lux meter you know of? I could keep my old one for accuracy, and use the new one for runtimes, where only relative accuracy matters. I'm hoping it's not more than $50.

BigWaffles said:

:thumbsup: +1 for the Extech Datalogging Light Meter, Model 401036. Beats checking in every so often and writing down the readings.


C.P.T.

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How do you like the 401036?

I have the 407026 and love it.

I came to the light... said:

So, what's the cheapest datalogging lux meter you know of? I could keep my old one for accuracy, and use the new one for runtimes, where only relative accuracy matters. I'm hoping it's not more than $50.

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PM inbound.

If you decide to buy an Extech let me know, I can save you some money.

-Michael

Texlite,

I love it. Here's a link to my test station.

https://www.candlepowerforums.com/posts/2866094&postcount=203

I've done a lot of runtime testing with it and it has worked well. The only problem is I'm starting to bump up against the 20,000 LUX capacity of the meter. If I keep going with my lights I'll have to get something that will measure higher.


C.P.T.

BigWaffles said:

Texlite,

I love it. Here's a link to my test station.

https://www.candlepowerforums.com/posts/2866094&postcount=203

I've done a lot of runtime testing with it and it has worked well. The only problem is I'm starting to bump up against the 20,000 LUX capacity of the meter. If I keep going with my lights I'll have to get something that will measure higher.


C.P.T.

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Could some sort of filter be used to lift the range of the meter?
You could easily calibrate the filter and then add it to your measurements, lot's of other measuring devices use that technique.
Norm

Norm said:

Could some sort of filter be used to lift the range of the meter?
You could easily calibrate the filter and then add it to your measurements, lot's of other measuring devices use that technique.
Norm

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That's almost what I did on one of my Malkoffs. The 9P with a Malkoff M60 was over 20,000LUX for the first couple of minutes. I put a small piece of black foam inside the lightbox to absorb some of the output and it dropped it by appx. 700LUX (verified with 2 other lights). I just added the 700LUX back into the final data measurements for the graph.

This will work for the occasional light but I would rather find a meter with calibrated sensors that I could swap out or a meter with a broader selectable range. Either way, I'm not actively looking for another meter quite yet.


C.P.T.

BigWaffles said:

This will work for the occasional light but I would rather find a meter with calibrated sensors that I could swap out or a meter with a broader selectable range. Either way, I'm not actively looking for another meter quite yet.


C.P.T.

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If you don't want to change out your meter, you could always approach the problem from another direction.

Change out the lightbox. By using a larger lightbox you would decrease the overall reading resulting in an increased range your able to measure.

It would be easy to calibrate by using some of your existing lights.

-Michael

csshih said:

yeah, I don't think there are that many alternatives.. maybe if you could get a camera timed to take pictures every minute? maybe a webcam?

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I did that for a runtime graph for the Kingpower K2.

I came to the light... Webcams tend to be fairly inexpensive these days. either way i will wager that its cheaper than buying a new Datalogging lightmeter.

My set up works only relatively to itself, but it DOES give you runtimes.

You have to download the Microsoft (if youre using microsoft) pack thingy. it give you a few applications, one of which lets you use the webcam itself. google it, im pretty sure it is findable.

Just set up some kind of diffusing unit (i used an opaque white coloured cap thing, and toilet roll tube to space it away from the sensor).The toilet roll also isolated the sensor from ambient light

Then, just set up your Lightmeter's Range properly, and set up your Camera so that it will snap every few minuites or so at the screen of the lightmeter. I would at least check in on your set up every 15-30 mins. Do note that as the light starts falling out of regulation, it will drop, FAST, so you might want to change the capture time to a few seconds. Oh and make sure you have some space on your harddrive for the hundreds of pictures there will be.

after that, just spreadsheet the whole thing lux/elapsed time and graph it.

If you have nothing better to do, i suggest renting a movie and watching it while waiting. i watched Casino Royale.

Crenshaw

Crenshaw said:

...Do note that as the light starts falling out of regulation, it will drop, FAST, so you might want to change the capture time to a few seconds. Oh and make sure you have some space on your harddrive for the hundreds of pictures there will be.

after that, just spreadsheet the whole thing lux/elapsed time and graph it.

Crenshaw

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"Hundreds of pictures"????
That might work for a shorter running light. One of my tests ran for over 8 days. I had the meter set to log every 30 seconds and still ended up with over 21,000 entries. Capturing a picture every 3 minutes on a light that runs for 5 hours will get you 100 pictures. Just trying to give an idea of the scope of manual logging.


C.P.T.

BigWaffles said:

"Hundreds of pictures"????
That might work for a shorter running light. One of my tests ran for over 8 days. I had the meter set to log every 30 seconds and still ended up with over 21,000 entries. Capturing a picture every 3 minutes on a light that runs for 5 hours will get you 100 pictures. Just trying to give an idea of the scope of manual logging.


C.P.T.

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I only did a High mode runtime test...IM guessing that on lower modes, you can take longer durations

Crenshaw

To get a good idea of the runtime of a flashlight I use a home integrating "T" that I made out of a 4" white plumbing "T" and have plugs on the 2 ends that each has a CDS photocell mounted on it. The flashlight lays in the bottom of the "T" and the business end points inside the "T" . The light from the flashlight never shines directly on the photocells. The whole setup is inside a closed box so that ambienI light doesn't affect the readings. I connect the photocells in series and connect them to a DVM with a RS-232 output (only $70 at Radio Shack) to a computer with data logging software. It's not calibrated to anything, but I can get relative brightness between flashlights and flashlight runtimes on different kinds of batteries. Testing my new Gerber Tempo on alkalines right now. Test has been running for over 11 hours. I screen capture the graphs at the end and the saved data files are text and can be imported into Excel. The DVM/logging software can save data as volts, amps, frequency, etc, (any setting on the meter).

OK, thanks to all of your help and a bit of research, I've found a solution

Here's my solution for others in a similar dilemma: measure the light output with the lux meter, and point a webcam at the lux meter. Use 1-more webcam to capture a picture every 30 seconds (or set the interval), then go through the images manually, recording the numbers. (It was surprisingly hard to find software that does this simple task AND actually works with my built-in webcam...)

Now what would be really nice is if I could automatically extract the numbers from those images, but it works for now.

hmm.. extracting numbers?

search up "OCR" software on the web. there might be some you could use..

csshih said:

hmm.. extracting numbers?

search up "OCR" software on the web. there might be some you could use..

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Thanks, I'm looking into it. It sounds like there should be some freeware out there.