Photocell Question

[mcasey1]

I am planning to use a silonex NSL-32 photocoupler that I got from Smallbear in my tremulus lune build.  There are four leads on the component, which looks like this:



short leads on left, long on right

My question is, which leads are from the LDR and which leads are from the LED?  Also there is a small grey dot by one of the short leads, does this indicate polarity?

[R.G.]

The fat, square leads are the LED, the skinny round ones are the LDR.

The gray dot is almost certainly a polarity marker, but it's easier to test it experimentally. Hook your DMM set to 2Mohm scale on the LDR. Now take a 4.7K resistor and a 9V battery in series and connect them to the LED leads. One way will do nothing, the other way will make the DMM go to low resistance.
When you find the low-resistor way, the battery + is going to the anode/arrow side and the battery - is going to the cathode/bar side, both perhaps through the resistor depending on where you put the resistor.