Picked up some electronic bits on the way home:
Thought I would see how the clear tube behaved in the infrared spectrum:
the LED by itself:
the LED through the empty tube:
the LED through the tube with water in it:
Am I imagining things or is it much brighter with the liquid in the tube? That is not what I expected.
P.S. Here is the intended display device
Edit: Apparently water vapor is a good IR blocker, which explains the results. Will need to retest with gasoline.