Influence of summer daylight saving time on scattered erythemal solar ultraviolet exposures.

The research question of whether there are any influences in the scattered or diffuse erythemal UV exposures to a horizontal plane over a five month period due to the change from standard time to daylight saving time, has been investigated by using physical measurements and applying them to both standard time and daylight saving time. The diffuse erythemal UV was considered for fixed lunch break times and fixed morning and afternoon break times. The cases considered were for groups of the population who are predominantly indoors and who spend their break times outdoors in shade. The biggest influence on the diffuse UV exposures of changing to daylight saving time is the timing of the outdoor meal and break times. The change causes a reduction in diffuse erythemal exposure for early or morning breaks and an increase in the diffuse erythemal exposure for late or afternoon breaks. Similarly, for the lunch break times, the changes in exposure are influenced by the timing of the break with respect to solar noon. Indoor workers who take their breaks outside in a shaded area may have a change in their exposure to diffuse UV due to a shift to daylight saving time, however the magnitude of this change and whether it is a positive or negative change in exposure will depend on the timing of the break. The increase in diffuse UV exposure due to the afternoon break may be negated by the decrease in exposure due to the morning break. In this case, the effect on diffuse UV exposures due to changing to daylight saving time will be minimal.