keywords: Diurnal Variation, Solar Irradiance, semi-monochromatic, Wavelength channel
Solar measurements were made at Wukari (Latitude 7.9303oN, Longitude 9.8125oE) using an EKOMS 120 sun photometer with half band width of 5nm and nominal wavelength of ±2.0nm at four semi-monochromatic wavelength of 430nm, 453nm, 640nm and 669nm. These wavelengths are the peak of the photosynthetic absorbance of green plants and algae. The filters were interference filters which allow direct solar radiation only. These wavelengths are variously referred to as channels 1, 2, 3 and 4. The mean optical depths measured in the months of October, November and December of 2020 are 0.8, 1.0, 0.4 and 0.7 respectively. This is a result that shows improvement over values deduced from literature. The peak absorptions occur at channels 1, 2 and 4 with a minor peak at channel 3.