Phycomyces is mediated by UV and blue light.
Blue light mediates positive phototropism while far-UV light mediates negative phototropism.
To better understand the mode of interaction of far-UV with blue light we performed phototropism experiments in which sporangiophores were placed for 4 h between sources of 280 and 454 nm light coming from opposite directions. Under conditions of bilateral irradiation the blue light substantially reduced the far-UV elicited phototropism. In the presence of tonic red light the antagonism between far-UV and blue light was greatly reduced. Red light, which by itself is phototropically ineffective, also reduced phototropic bending elicited by either far-UV or blue light.