The spectral transmittances of two different glass types have been measured in a spectrophotometer. Both glass types have been investigated with and without a Sunarc anti reflection surface (AR surface). The transmittance data for the AR treated samples have been used as input to the AR treatment process in order to improve the solar transmittance for the glass samples. A standard flat plate solar collector has been tested in the indoor solar simulator. The purpose of the tests was to evaluate the improvement in collector performance that can be expected by replacing the standard cover with a similar cover supplied with a Sunarc antireflection surface (AR-cover).