Greetings from Johannesburg... Supposedly winter here, but a nice 15C and sunny right now at 10h30.
I'm pretty sure there's more to it than an LDR is an LDR is an LDR, but even adafruit just has "an" LDR for sale without saying what its specs are.
I've seen them in physically different sizes, so that's one difference.... I would surmise they have different resistance to light (some kind of ohm / lux thing maybe?) and probably a time to react (like a delta ohm per delta lux per second?). One of my local suppliers lists min and max resistance, but that and the size is all I've been able to find so far.
So, what's the gen on LDR specs?
Because they are made from cadmium sulphide, they shouldn't be used. Most component companies don't even sell them any more.
Hmmm yes I see it's regarded as hazardous Leon, as explained here for instance... http://nj.gov/health/eoh/rtkweb/documents/fs/3081.pdf
But given that they are still sold, and that there must be zillions around, I'm still keen to know how they are specified.
The get specified by the dark current, that is the current when they are in the dark, and the light current - guess what that is.
As these are resistive this currents are given at a set voltage - this depends on the data sheet.
You will also see the light pulse curve, that is sudden exposure to a step change in light and how the resistance changes over time, this will be slow.
What are folks using as alternatives? I've looked around some and have found lots of phototransistors, but these seem to be predominantly of the infrared variety.
Plenty of photo-diodes that respond to visible light are available.