Using the flashlight should start by turning it on.
Firing (mouse1) could give it higher intensity at a cost (visibility? Muzzle flash like Gun, perhaps energy drain on Fuel Jet and the Shielded player types)
Jetting (mouse2) should do that attack thing, very low damage (15-20, once a second. It's really better to switch weapons)
Pressing Light (L) should use the tool (if you have one) and turn it on, or turn the light off if you are using it. Perhaps using the standard Light is disabled in minigames when the Flashlight is enabled on the server?