Researchers are studying people's exposure to sunshine and their Vitamin D levels.
An ultraviolet dosimeter, invented in New Zealand, uses an electronic sensor to measure radiation.
The information can be downloaded to produce a daily graph of personal exposure to UV rays.
The dosimeters are being used in a study between the National Institute of Water and Atmospheric Research, the University of Otago and Auckland University.
Participants wear the dosimeter on their wrists, and keep a diary of the clothes they wear and how much time they spend outdoors.
Researchers then measure their Vitamin D levels to identify which groups of people may be deficient in the vitamin and during which seasons.
