function res=temp_radiacyjna(I,lambda);
% temperatura radiacyjna - Brightness Temperature
% input:
% lambda in [um]
% I (m^2 um^-1)

c=299792458;     %  ms **-1
h=6.6260755e-34; %  Js
k=1.380662e-23;  %  JK-  1
lambda=lambda*1e-6;
I=I*1e6;
res=h*c/(k*lambda*log(1+(2*h*c^2/(I*lambda^5))));

