•
•                                        Ir          (η2 -  η1)2                    
•    Reflectance  =  R  =   ----   =  --------------
•                                        Ii          (η2 + η1)2
•
•Where Ii and Ir = incident & reflected intensity
•
•For radiation going from air (η = 1.00) to glass (η = 1.50) as shown in previous slide
•
• R  =  0.04  =  4 %
•
•Many surfaces at 4 % each (i.e., many lenses) can cause serious light losses in a spectrometer.  This generates stray radiation or stray light.