This command is used to check and adjust the orientation of surfaces in your model. In general, the orientation of surfaces is not important for Radiance as it is with other lighting analysis tools. However, to calculate the distribution of daylight with glazings to be treated as a "light source", it is necessary to have the glazing surface correctly oriented. Material surfaces do not need correct surface normal orientation. To use this function, go to Radiance—>Tools—>Adjust Surface Normals. Then, as you are prompted, select the glazing surface in your drawing. A red arrow will appear within the window. A correctly oriented surface normal for a window or skylight should be pointing in the direction of daylight travel from brightest to dimmest regions. The command line asks you if you want to flip the surface normal. Type "N" if the arrow is pointing in the correct direction and "Y" if you want to switch it. If the direction of the surface normal is not as you expected and cannot be reversed with this tool, then the window surface needs to be recreated.
If the red surface normal arrow does not appear it may be that you are checking an object that Desktop Radiance can't figure the front/back of, for example an exploded ACIS solid. The surfaces of an exploded ACIS solid will have normals pointing outwards. If the surface normal you are checking is not that of a surface of an exploded ACIS object and you don't see the red surface normal arrow, see Preferences.
Use the Right Hand Rule to correctly orient glazing surfaces: Imagine placing your right hand against the wall with the window, with your thumb pointing in the direction that the light travels. Your four other fingers now curl in the direction that the vertices should be created to obtain a properly oriented surface.
