Linear glass Fresnel lenses have been experimentally investigated by means of a narrow He-Ne laser beam, both at normal incidence and at various combinations of meridional and sagittal angles of incidence. Both rays incident on the flat and on the grooved side were studied. Results were compared with previous ray tracing results by Franc et al. The experiments suggest, contrary to ray tracing, that the grooves should face the sun in other than sun-tracking applications.