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This article in AJ

  1. Vol. 63 No. 5, p. 743-748
    Received: Mar 12, 1971

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Light Intensity and Sunfleck-size Distributions in Plant Canopies1

  1. J. M. Norman,
  2. E. E. Miller and
  3. C. B. Tanner2



A theory predicting the gap-size distribution of a canopy of horizontal, azimuthally symmetric, randomly located, flat leaves of any shape is compared to measurements in sumac (Rhus typhina L.), sunflower (Helianthus annuus L.), and an artificial canopy. Light intensity distributions of the solar beam component on a horizontal surface below these canopies are predicted by combining the gap-size distribution theory with penumbral effects of the finite solar disc. These predictions of the beamcomponent distribution are then combined with average diffuse penetration theory and a new scattering theory to produce a final light intensity distribution for comparison with measurements from a miniature light sensor in visible and near-infrared wavelength bands. The agreement is good and indicates that sizable penumbra effects occur in canopies only 2 m in height.

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