SNAP Reflectance to Radiance parameters?!

Hi why when I want to use Reflectance to Radiance in SNAP (Thematic land processing) and I use Sentinel 2 band 3 as my input. It asks me incidence angle, solar irradiance and U? What are these? Isn’t it supposed to recognize them itself? I couldn’t find them iin metadata!Is there any other way to convert Sentinel 2 Level C1 (which is reflectance) to Radiance?
Please help me resolving this
Thanks in advance

A post was merged into an existing topic: Sentinel 2 MSIL1C conversion to Radiance!