soldering LEDs for use as sensors

Hi. So I'm trying to use an LED as a light sensor by applying a positive voltage to it backwards and then counting down how long it takes to get to 0V, similar to this:

the problem is, whenever I try to solder anything on to the LED, it takes far less down to count down. I'm guessing I'm changing its capacitance, but I'm not sure. Am I just epically bad at soldering or is there some way to not screw up the LED?

If it discharges faster this means you are adding more leakage current.

What are you soldering to it?

Also its possible to damage the LED by soldering for too long (LEDs are often more sensitive than silicon devices to heat), thus changing the natural dark leakage current.