LDR Consistency?

[selfdestroyer]

Question, I am trying to sort a bunch of LDRs I have collected over time and pair them up. I Do have some that are already bagged up and I wrote on the bags who I go tthem from (Tayda, SmallBear, MKlec ect.) and what models they are. As I was testing the loose LDRs I found that I was not getting consistent readings from my DMM. I would hookup the leads to alligator clips and the clips to the LDR legs, set the DMM to resistance and auto-ranging all the way up to 40M. I would then use a light source/mag light to shine on the LDR and take the reading then wrap my hand around the LDR and take a reading. On the light end of things they would bounce around quite a bit from 1k - 1M even in direct light. I thought it might be a bad batch of loose china made LDRs so I started checking the bagged ones I had labeled. I was still showing my Smallbrear 8001's were 100k-150k out of spec in light.

So my questions are:
Am I testing these properly?
Are LDR's really inconsistent from the datasheets?
Do I need another beer?

Side note: I never had an issue with my Fluke DMM with checking resistance on other parts and I even used the wall wart instead of batteries just to make sure.

I have also collected most of the datasheets for the CdS LDRs I am using.. or think I am using... no making on LDRs (that I can see) are driving me nuts.

I also seen this older thread but it did not really answer my questions
http://www.madbeanpedals.com/forum/index.php?topic=8934.0

Cody

[m-Kresol]

I think LDRs are kind of bad to test. Their photoresponse is (I guess) dependent on frequency of the light you use, i.e. colour. Not sure why they would vary so much, but I had similar experiences with mine. Also, response times are comparably high anyways.

Do I need another beer?

That question I can answer Yes.

[drolo]

In short: LDR Consistence = none :-)
They are usually all over the place. Vactrols seem a bit more consistent but have not really made any tests to confirm the assumption.

[culturejam]

It might be partially the test method, but there is also some variability in the performance of LDRs.

I would say to test with the same type of light you plan to use in a circuit. So maybe a red LED? Or maybe test them with multiple colors (wavelengths)? Like Red / orange / yellow and something goofy like green?

Also, you might want to use a meter with a "hold" function. Back when I had an Atlas LCR, I tested some LDRs and they were more or less consistent. The meter would wait until a value stabilized and then hold that number on the display. So I could turn off the light, hit the test button, wait for a result and then turn the light back on and see what it was when dark.

[selfdestroyer]

Thanks peoples.. some good ideas.

Funny story, my wife came out in the garage last night while I was testing these. I had my hand over a LDR on the desk and she thought I caught a bug under my hand on my bench. She kept saying "you better not throw it at me" haha I would never do that.... :]

Cody

[stringsthings]

Thanks peoples.. some good ideas.

Funny story, my wife came out in the garage last night while I was testing these. I had my hand over a LDR on the desk and she thought I caught a bug under my hand on my bench. She kept saying "you better not throw it at me" haha I would never do that.... :]

Cody

Don't ya hate it when someone throws an LDR at you?