Spectro-directional surface measurements can either be performed in the field or within a laboratory setup. Laboratory measurements have the advantage of constant illumination and neglectable atmospheric disturbances. On the other hand, artificial light sources are usually less parallel and less homogeneous than the clear sky solar illumination. To account for these differences and for determining for which targets a replacement of field by laboratory experiments is indeed feasible, a quantitative comparison is a prerequisite. Currently, there exist no systematic comparisons of field and laboratory measurements using the same targets. In this study we concentrate on the difference in spectro-directional field and laboratory data of the same target due to diffuse illumination and applied a correction term proposed by (Martonchik, 1994). Spectro-directional data were obtained with a GER3700 spectroradiometer. Additionally, a MFR sun photometer directly observed the total incoming diffuse irradiance. In the laboratory, a 1000W brightness-stabilized quartz tungsten halogen lamp was used. For the first direct comparison of field and laboratory measurements, we used an inert and highly anisotropic target with high angular anisotropy. Analysis showed that the diffuse illumination in the field is leading to a higher total reflectance and less pronounced angular anisotropy.