Influence of light on natural indigo production from woad (Isatis tinctoria)

In woad (Isatis tinctoria), field observations indicated, that after periods of dry sunny weather, indigo yields increased significantly, suggesting that light intensity and quality affected indigo precursor production. Therefore, woad was grown under different light intensities and in the presence or absence of supplementary UV light. In general, plants supplied with more light produced more indigo than those given lesser light. When plants under greater light regimes were transferred to lesser light conditions, then indigo production declined. The opposite was also true, indicating that greater indigo production can be obtained from plants harvested after periods of increased sunlight.