Abstract :
The purpose of this work is to characterize the sky relative radiance and luminance distributions from the analysis of sky images
acquired using a monochromatic CCD wide angle lens camera. The proposed methodology is based on the reduction of the number
of the gray levels from the original image, in order to sharpen the different regions of the sky hemisphere, resulting in low level gray
scale maps. In these maps each gray level is related to an intensity level and each pixel is associated to a sky direction. An experimental
system that is able to simultaneously supply images from the sky and solar irradiance data was developed using a commercial CCD camera.
The sky relative radiance and luminance distributions for different sky conditions were also determined. The resultant maps agree
with observations of the main characteristics of sky radiance and luminance distributions.
2007 Elsevier Ltd. All rights reserved
