The complex amplitude ratios for light are defined as: rTM = ErTM / EiTM tTM = EtTM / EtTM I've done the derivation from Wikipedia and see that (n2/n1) * tTM = rTM + 1. But I don't understand what is going on physically. I understand that these values are not power or intensity so I can't really invoke conservation of energy (or can I?). Why is r + 1 = t for TE light, but not TM? Thanks.