Ultraviolet light is an effective sterilization agent. Convenient mobile sterilization devices are described herein that, in certain embodiments, provide indications to a user of how much sterilizing light is required for a given sterilization goal and how much light has been applied to a surface towards that goal. Users can move the devices across a target surface as needed to sterilize or disinfect the surface, with the device tracking the dosage applied to the surface. One embodiment of a mobile device that comprises an ultraviolet C (UVC) light source, a distance detector, an indicator, and a microprocessor that receives data from the distance detector for calculating an intensity of the light from the source on a target surface and for calculating a dosage of the light on the surface to provide a signal to the indicator when a predetermined dosage is achieved.
