Both show the light performance of a diamond. They show where there is light leakage and how light is reflected back. You want a diamond that reflects a lot of light back. Idealscope uses a red reflector. You want there to be as few areas of white or faded red as possible. ASET is similar, but it shows the angles where light is entering the diamond. All you really need to know is that you want to see as little white as possible.