This video says about itself:
Bats hunting over a small river around midnight in July, in northern Germany. Video taken from a digital night vision device (Nitemax), using IR-light, audio taken from a heterodyning bat receiver (made from a kit).
Light usually disturbs bats, as it makes them more vulnerable to predators.
The research aims at finding out which colour is least disturbing to the bats, so that if lights are built that colour may be used.
Provisional results are that bats hate white or green light, and are less disturbed by yellow light.