The performance of solar systems (thermal or phorovoltaic) is influenced by the ability of the glazing to transmit solar radiation to the collection surface, besides other factors, such as, incident radiation, tilt of collector, properties of materials, operating strategy, surroundings, etc. This paper discusses the influence of dust on the transmittance of a 0.2-mm-thick low-density polyethylene (LDPE) glazing used commonly in solar air heaters. The reduction in transmittance due to;various dust deposition densities of Bangkok clay (size 53-75 mu m) has been measured and a correlation relating the dust deposition density and the transmittance given. Experimental observations of natural dust accumulation on an inclined (15 degrees) LDPE glazing at a tropical climatic condition during a 30-day period indicates a dust accumulation of 3.72 g/m(2) and is found to reduce the global transmittance of the glazing from about 87.9% to 75.8%. (C) 2000 Elsevier Science Ltd. All rights reserved.