Okay I've collected some data. the first row's I didn't do anything, then I tried covering one of the diodes slightly, then I put my finger on it covering it completely, finally I tried covering the other diode.
code:
x=0
lightLevel1=1530
lightLevel2=1530
x=-255
lightLevel1=1530
lightLevel2=1785
x=-1530
lightLevel1=0
lightLevel2=1530
x=255
lightLevel1=1785
lightLevel2=1530
The diodes where placed fairly close to each other, so when I tried covering one, I accidently might have covered the other slightly. But I can't see why this would affect the outcome. 