1) Variety Koh No. 7 of corn plant with 3 different planting densities (5, 10 and 20 cm intervals) was grown in green house to study the status of light extinction in the canpy. Light extinction coefficient K in Monsi and Saeki's formula can be divided into following two components according to Monteith's model (1965). One is light transmission rate through d single leaf (τλ) and another is a parameter S representing the average arrangement and orientation of the leaves. S is the fraction of incident radiation that passes through a layer without being intercepted by any leaf or stem. 2) Stratified clip method was adopted at regular intervals to estimate light extinction coefficient K. Light intensity under the canopy was mesured with sillicon blue cell (SBC) covered with infrared absorbing filter. 3) Light transmission rate through single leaf (τλ) was measured with a spectro-photometer (Hitachi EPS-3T type) using jointly the integrating sphere and an opal glass in order to apply to Monteith's model. 4) According with the increase of planting density and the advance of growth stage, light extinction coefficient K declined and light transmission rate (τλ) through single leaf were enhanced. However, being on Monteith's model, it became clear that the light transmission rate (τλ) scarcely affected light extinction coefficient K, whereras the parameter S played an important role in K.
