“…It is based on the principle, derived from theoretical expectations and syntheses of canopy-scale measurements (Healey et al, 1998;Hollinger et al, 1994;Kanniah et al, 2012;Niyogi et al, 2005;Norman, 1993;Roderick et al, 2001;Urban et al, 2007), that the efficiency of carbon uptake is usually higher under diffuse light conditions that accompany cloudy and/or hazy skies than it is under clear sky conditions. The underlying mechanism for this increase in efficiency is the increased penetration of light into deeper layers in the canopy under diffuse light conditions such that substantially more leaves operate in partial light conditions -under which photosynthesis is inherently more efficient -rather than in deep shade or saturated light (Campbell & Norman, 2000;Farquhar & Roderick, 2003;Gu et al, 2002;Horn & Schulz, 2011;Kanniah et al, 2013;Kanniah et al, 2012;Mercado et al, 2009;Roderick et al, 2001;Spitters, 1986;Williams et al, 2014). This phenomenon has been widely incorporated into bio-physical canopy models (Alton et al, 2007;Anderson et al, 2000;Choudhury, 2000Choudhury, , 2001ade Pury & Farquhar, 1997;Hammer & Wright, 1994;Jenkins et al, 2007;Norman, 1980;Norman & Arkebauer, 1991;Sinclair et al, 1992;Wang & Leuning, 1998).…”