The invention relates to UV light modules that generate UV light. The UV light module includes: a substrate； a light source mounted on a top surface of the substrate, the light source generates output light； a detector mounted on the top surface of the substrate, the detector detects light incident thereon； and a lens disposed over the light source and the detector. The lens includes a surface on which a portion of the output light is internally reflected and the portion of the output light travels through the lens to the detector.
