Right clicking on a photo with the Lighter Tool produces a popup menu showing all the lighting filters that can be tweaked. To tweak a filter, select that menu item. The mouse cursor will disappear and you can adjust the filter value by dragging the mouse up and down (the photo will change accordingly). Clicking the mouse again will end the tweak. You can also just point and drag with the left mouse button on the photo, where motion up and down will adjust brightness and where left and right will adjust contrast.