The performance as well as the illuminating abilities of a tubular light guide system furnished by two-component glazing on its base is analyzed. The glazing consists of two optical elements: a Lambertian diffuser and clear glass. The inner parts of circular glazing behave like Lambertian diffuser while the edges of the glazing are built of clear glass. The illuminance distributions on the two-component glazing and the workplane situated below the light guide are simultaneously calculated. The presented concept guarantees: an improved energy utilization, an enhanced interior light conditions (especially under low solar elevation conditions), and an eliminated light excesses which are typical for fully transparent optical interfaces. (C) 2008 Elsevier Ltd. All rights reserved.