This level is a little tricky, since you don't have much room to experiment with the prism. My apologies for not giving an easier prism level first.
If you haven't figured out what the prism does, play with it a bit.
(scroll down for more)
You should be able to use the prism to hit all three colored
targets correctly using just one bender and one reflector.
(scroll down for more)
If you push things a bit, you should be able to get two of the
white targets lit up as well, but the third one might be stumping
you. If that's the case, take a look at the next hint.
(scroll down for more)
Assuming the one you're stuck on is the lowest, center white target,
the fact it's in the tunnel like that means you can't possibly hit
it once the white beam has bounced off the bender. So you'll
have to hit it earlier. Just one more hint on this.
(scroll down for more)
The second law of evil game designers is to not be predictable; this is a case where the the first law of evil game designers does not apply.