Relativistic Doppler effect invisible ultraviolet wavelengths, infrared light is blueshifted into the visible range. Precisely what changes in the colors one sees depends on the physiology of the human eye and on the spectral characteristics of the light sources being observed. The Doppler effect (with arbitrary direction) also modifies the perceived source intensity: this can be expressed concisely by the fact that source strength divided by the cube of the frequency is a Lorentz invariant This implies that the total radiant intensity (summing over all frequencies) is multiplied by the fourth power of the Doppler factor for frequency. As a consequence, since Planck's
Ultraviolet communication in butterflies to detect UV light and responds maximally to ultraviolet light at approximately 350 nm. Therefore, a visual pigment that responds to ultraviolet light is the mechanism behind ultraviolet light perception. White Cabbage Butterflies, "Pieris rapae crucivora", use their private ultraviolet communication system to initiate mating behavior. In this species, ultraviolet reflection is sexually dimorphic with females exhibiting the ability to reflect ultraviolet light of 380 nm to 400 nm and males being less able to reflect UV. Males who perceive an ultraviolet reflection from a female initiate a courtship behavior that involves approaching the female and attempting to copulate. Females