1. To reveal the convertibility between different indices of microsite light environment, relative photosynthetically active photon-flux density (R-PPFD) and relative illuminance (RI) were measured with the ratio of red light to far-red light (R/FR) simultaneously below various types of vegetation: temperate riparian deciduous broadleaf forest, coniferous forest, mixed forest of evergreen broadleaf and coniferous trees and cool-temperate deciduous broadleaf forest, and in rice paddy in summer. 2. Within and throughout the vegetation, R-PPFD and RI were strongly correlated, but the slopes of the regression equations significantly exceeded 1, and differed among the vegetation types and varied seasonally. 3. R/FR decreased with decreasing R-PPFD. The difference between RI and R-PPFD increased with decreasing R/FR: the darker the microsite, the larger the 'error' of the evaluated light availability if RI was used. 4. RI data can be converted to R-PPFD. Conversion from RI to R-PPFD would allow more reliable data comparisons among the different vegetation types and among studies that use different methods to measure the light environment.
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