If you follow Mike's LED post and use normal led's there is a program posted here somewhere that gives the code for a function to read the time it takes for an LED to dissipate its charge to zero . If you can't find it by searching this thread then say so and I will go find it.
Surprisingly the LED used only as a light sensor can be reversed . No resistor is needed. However you are working with wire and capacitance and they vary widely from manufacturer to manufacturer . If you want a longer lead on an LED the only success I have had is with a single core shielded coax type cable with the shield as one of the wires,connected to negative , and the core as the other. Two wire shielded cable does not work and neither does twisted pair.. I think they pull in radio wave voltage in the area
The above single wire/shield works on the coax theory that the signal going into the coax comes out the same at the other end provided the capacitance in the cable does not vary so you should be able to use any length.