Usually, people mount the bar flat against the underside of the shelf or cabinet; however, you can tilt the light bar up to 10° from horizontal by adjusting which grooves on the side of the light you use for clip. See detailed pictures.
Angle Brackets are available as an option, so you can tilt the bars 45° from horizontal, with additional adjustment possible, from 23° to 53°. Screws are only 0.4 inch (1 cm) long, so they won't fully penetrate most shelves or cabinet bottoms.