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• We measure yield and protein of shaded lentil in southern Australia and Chile. • The most sensitive period was pod emergence, between 50–126 °Cd after flowering. • Grain number and biomass accounted for most of the variation in yield. • Grain protein concentration varied according to a bi-linear model. • Protein yield tracks grain yield and is partially buffered by late season protein. Lentil is a cool season grain legume produced primarily in the Mediterranean and temperate regions of the world where water and heat stress in critical developmental windows constrain yield. The effect of stress on yield depends on the timing, intensity and duration of stress; here we focus on timing relative to phenological development. To determine the critical period for grain yield and grain protein, we compared unshaded controls and crops exposed to sequential 10–14 d shading periods using two locally adapted varieties at Roseworthy, south-eastern Australia, and Valdivia, southern Chile. Yield of unstressed controls varied from 1 t ha−1 at Roseworthy to 7 t ha-1 at Valdivia, and grain protein from 22.0 % at Valdivia to 27.6 % at Roseworthy. Irrespective of growing conditions, the most sensitive period was at 50–126 °Cd after flowering, around pod emergence. Grain number and biomass accounted for most of the variation in yield. Grain protein concentration varied according to a bi-linear model, with minor reduction (<10 %) before a developmental threshold (i.e. flowering at Valdivia, ∼ 200 °Cd after flowering at Roseworthy) and a linear increase after the threshold. Protein yield tracked grain yield, but the increased grain protein concentration partially buffered the effect of post-flowering stress. [ABSTRACT FROM AUTHOR]