Abstract Background and AimsMost optical devices for indirect measurement of leaf area index (LAI) from canopy-transmitted light are tailored for homogeneous canopies, thus limiting their application to discontinuous canopies such as vertically trained vineyards. This study evaluates the influence of sun position on the reliability of LAI estimates provided by a ceptometer and proposes a measurement protocol for use of such instruments on vineyards under direct illumination. Methods and ResultsCeptometer readings at several sun elevation and azimuth angles were recorded in two fields. LAI estimated at different sun positions using several measurement protocols were then compared against destructive leaf area measurements. The best results when the sun position departs from the zenith (sun elevation .