Our UV dosimeters use an AlGaN photodiode as the UV sensing element. This is mounted directly behind a polytetraflouroethylene (PTFE) UV diffuser to achieve a good match to the flat cosine response of human skin. The PTFE diffuser also acts as weather-proof case, which is sealed against a lightweight backing plate that also contains a micro data port used to retrieve the data. The dosimeters are small (35 mm × 13 mm) and lightweight (19 grams) and can be pinned to clothing using a safety clasp or attached to the wrist using a fabric watch strap. The AlGaN photodiode produces a photocurrent when illuminated with UV radiation. This is amplified using an electronic amplifier and converted to a digital signal using a 10 bit analogue-to-digital converter. This digital signal is then proportional to the intensity of the incident UV radiation weighted according to the erythemal spectral response of the AlGaN photodiode. The sampling functionality is provided by a microcontroller and solid-state memory that records this digital signal at user-programmable time intervals which can be as low as every four seconds to provide over 10,000 instantaneous UV intensity readings in a 12-hour daytime period. This temporal data can be integrated to give doses and dose rates at selected time intervals, e.g. daily, hourly, half-hourly. The UV dosimeters are powered by a small lithium 3.0 V coin cell which provides several months of operation that can be further extended through the use of user-programmable daily data recording start and end times which avoid data collection during night-time periods