Andrew,
you link a page with very complete instructions and a sample program. You say, the thing doesn't seem to work as described. You tinker around with the code, the thing still doesn't work.
Now you expect us give you some magic code change so that the thing works suddenly, while it's not even clear if that thing is even possible to work with the leds you use - or with any leds.
Doesn't that sound a little unreasonable to you too?
Perhaps you better check first the electric side if the described effect can be observed. If it's there, you might be able to measure it. If it isn't there, well, you'll never going to measure it no matter how often you post questions about it.
Instead of wasting all that effort, get a $0.49 photodiode. That's better, faster, easier, cheaper and works.
Korman