Measurements of global solar radiation within and outside the tropical forest were made on 7th november 1986 in the area of the Tucurui, Para. The intensities of solar radiation at 3 sensors distributed randomly on the forest floor and one sensor located in an open area (standar sensor) are avaluated and intercompared. The average solar radiation which reachead the forest was 4.7% of the incident radiation over an open area. The diferences among the measurements of sensors and the etandar eeneorwae atributed to heterogeneous spatial distribution of sunlight penetration into the forest floor.