Build 20180831 is now live on Steam, and Lux now has manual control over her flashlight. You can toggle the flashlight by pressing F on the keyboard (it’s remappable), or by pressing the Left Stick Button on your controller.
The game will still automatically switch the flashlight on and off at certain locations, but you can override that using this new functionality. As always, please let me know if you run into any issues. :)