The erythemal ultraviolet exposure for humans in greenhouses.

A spectrum evaluator has been employed to evaluate the erythemal exposure in late spring and late summer at three sites and five orientations at each site inside a glass greenhouse with black shadecloth over the glass roof. The maximum in the erythemal irradiance in the greenhouse is not necessarily at noon. Over a day, the maximum erythemal exposure occurred on the eastern side of the greenhouse in the morning and on the western side in the afternoon. The erythemal irradiance on the eastern side in the morning was higher by 26% and 50% for horizontal and vertical surfaces respectively compared with the same site at noon. On the western side the irradiance was higher by 45% and 78% for the horizontal and vertical surfaces respectively compared with the same site at noon. The erythemal irradiance inside the greenhouse does not vary as much during the day as it does outside; for example, for horizontal surfaces, the ratio of the erythemal irradiance outside to the average inside the greenhouse varies from 66 to 112 to 74 for the morning, noon and afternoon periods respectively. Over a 6 h period, the erythemal exposure to the shoulder for a standing posture in the greenhouse was 5 mJ cm-2.