Abstract: In order that an installation for coating panes of glass can be operated more reliably, the invention proposes a modification of the light barriers used in the installation. On the receiver side of these light barriers there is a row of individual cells which are more or less shaded according to the thickness of the glass pane passing through the ray path of the light barrier. Some cells always deliver a significantly reduced signal which can be evaluated as a reliable indication of the presence of an object in the ray path.