The fast and slow fading of radio signal transmissions or laser beam itself and its spare light confirm the presence of two kinds of collisions --- electron-photon and photon-photon collision. Photon transmissions of radio signals are either in consecutive dense photon groups in slow fading process or widespread group pattern in fast fading form. The photon transmission shapes are irregular and dynamical changes. The radio frequency shift and the wavelength reduction by the calculation demonstrate decelerations of radio/light transmission speeds due to the gradual reduced distance between two consecutive photon groups along the transmission pathway. Photons from radio signals are able to affect electron movements in radio signal receiving process and electrons able to kick photons into space during radio signal emission. The pattern of free electron movement under the influence of local electromagnetic force in antenna is consistent with the randomly dynamic changes of radio signal in space. The fast fading is due to the collision of consecutive photon groups of signals in slow fading with free photons in space. The mathematical equation for the relationship between light/radio transmission speeds before and after photons collisions is established. The equation is confirmed by the calculations of well-known difference of light transmission speeds in different media. The gravities from Earth and Sun play little role during light/radio transmission.