The spatial extent (SE) of the focal point (FP) of a parabolic dish reflector has been determined using a laser diode as a source of light. The laser diode measurements were compared with those taken using a Gardon radiometer where the sun is the source of light. This was done in order to determine if the laser diode technique can be used in place of the radiometer technique. A height of 0.267 m as measured from the vertex of the dish reflector has been determined as the optimum height to place the aperture of the receiver by both methods. An optimal radius of the receiver aperture was determined to be 0.16 m by use of the laser diode and 0.13 m by using the radiometer. The laser diode results show good agreement with the radiometer results. This means that the laser diode technique can be used to determine the SE of the FP. It can also be used to determine the height at which to place the receiver's aperture. Thus, the laser diode can be used in place of the radiometer in cases where the radiometer is not available. This technique has the advantage in that it does not require outdoor experimental setups. (C) 2010 Elsevier Ltd. All rights reserved.