# The Sun File

The sun file has the familiar block of lines at the top identifying it as a RenderWorld file and defining the color bands. Once again, this information shouldn't be changed.

           RenderWorld_data_file sun 1 1
           position_method_flag 0
           number_of_bands 3
           band_id 1 2 3
           intrinsic_irradiance 1372 1770 1877
           end

The only values in the sun file that should be changed by the user are the three values on the `intrinsic_irradiance` line. These define how bright the sun is above the atmosphere in the red, green, and blue bands, and are in physical units. The values shown are the actual values for our sun at Earth's distance, and shouldn't be changed for producing realistic images.

> When the user is rendering with other than three bands, the list of values on the `intrinsic_irradiance` line should match the number of bands actually used. In addition, the `position_method_flag` is presently not used, but is reserved for future uses. Do not change its value from `0`.

> The `intrinsic_irradiance` parameters define the scale of the intensity values calculated by RenderWorld. The values show here are representative values, in units of `Watts/(square-meter micron)`. The output pixel intensities of the rendered images are in units `Watts/(square-meter micron str)`. In principle, this information combined with light meters in the field could be used to calibrate the rendered images to real data, or to standard gray reflection cards.

Contents