This paper investigates the improvement of human thermal comfort while working in protected horticulture. Shading materials are used in order to decrease light intensity and air temperature in greenhouses in summer. Lettuce (Lactuca sativa L.) plants were grown under two environmental conditions : clear (high light intensity and high temperature) and under shading (low light intensity and low temperature) together with four human working patterns; whole day clear (control), AM shading (morning work), midday shading (midday work) and PM shading (afternoon work) . Plants that were grown under control and midday work conditions had increased numbers of leaves, dry weight, chlorophyll content and photosynthetic activity, as compared to those grown under morning and afternoon work conditions. There was an inferior thermal environment and poorer crop qualities were observed in the plants grown under the control condition. The present experiment suggests that midday work may be a suitable working time for lettuce production in shaded greenhouses during summer.
