The measurement and distribution of irradiance in clear and overcast conditions in four temperate forage grass canopies.
An instrument for measuring the distribution of irradiance in grass canopies is described; it demonstrated that light from an overcast sky was more uniformly spread throughout the canopy than light from a clear sky. Italian ryegrass cv. RvP, perennial ryegrass cv. S24, cocksfoot cv. S345 and Timothy cv. S50 had their own characteristic distribution patterns which were maintained in different light conditions; mean leaf angle was also constant, suggesting that angular structure was important in determining light distribution in grass canopies. It is suggested that the distribution of direct light from the sun may be described by Monteith's S function.