The invention is drawn to a method of producing a transparent diffusive OLED substrate comprising the following successive steps: (a) lapping one face or both faces of a flat translucent glass substrate with an abrasive slurry, so as to obtain a flat glass substrate with at least one roughened surface having a roughness profile with an arithmetical mean deviation R a of between 0.1 µm and 2.0 µm, preferably between 0.15 µm and 1.5 µm, more preferably between 0.2 and less than 1.0 µm and most preferably of between 0.25 µm and 0.8 µm, (b) coating the roughened surface or one of the roughened surfaces with a high index glass frit having a refractive index of at least 1.7, preferably of between 1.7 and 2.2, the amount of the high index glass frit being sufficient to completely cover the roughness profile of the roughened surface after melting of said frit ; (c) heating the coated substrate to a temperature above the melting temperature of the high index glass frit and below the softening temperature of the underlying substrate, so as to form high index enamel on one of the roughened surfaces.