8.2. Solar radiation
In recent years, various modifications have been made to the spectral characteristics of greenhouse covers. These alterations are designed to protect greenhouse-grown crops from herbivorous insects and insect-borne viral diseases and to suppress proliferation of foliar diseases. These goals are achieved through partial or complete absorption of solar UV radiation (Raviv and Antigunus, 2004). However, UV radiation is also essential for honey bee and bumble bee navigation (Sakura et al., 2012). Use of UV-absorbing sheets as well as UV-opaque covers (such Perspex and fiberglass) can therefore be damaging to bees’ pollination activity in enclosures (Dag, 2008). The degree of UV absorption can be evaluated using UV sensors (10–400 nm), and opacity to UV radiation can be assessed by observing the shadow of an object in the enclosure through a UV filter; if a distinct shadow cannot be seen, then the UV radiation is diffuse.