<P> The connection between the visible spectrum and color vision was explored by Thomas Young and Hermann von Helmholtz in the early 19th century . Their theory of color vision correctly proposed that the eye uses three distinct receptors to perceive color . </P> <P> Many species can see light within frequencies outside the human "visible spectrum". Bees and many other insects can detect ultraviolet light, which helps them find nectar in flowers . Plant species that depend on insect pollination may owe reproductive success to their appearance in ultraviolet light rather than how colorful they appear to humans . Birds, too, can see into the ultraviolet (300--400 nm), and some have sex - dependent markings on their plumage that are visible only in the ultraviolet range . Many animals that can see into the ultraviolet range, however, cannot see red light or any other reddish wavelengths . Bees' visible spectrum ends at about 590 nm, just before the orange wavelengths start . Birds, however, can see some red wavelengths, although not as far into the light spectrum as humans . The popular belief that the common goldfish is the only animal that can see both infrared and ultraviolet light is incorrect, because goldfish cannot see infrared light . Similarly, dogs are often thought to be color blind but they have been shown to be sensitive to colors, though not as many as humans. . Some snakes can "see" radiant heat at wavelengths between 5 and 30 μm to a degree of accuracy such that a blind rattlesnake can target vulnerable body parts of the prey at which it strikes, and other snakes with the organ may detect warm bodies from a metre away . It may also be used in thermoregulation and predator detection . (See Infrared sensing in snakes) </P> <Table> <Tr> <Th_colspan="4"> </Th> </Tr> <Tr> <Th> Color </Th> <Th> Wavelength </Th> <Th> Frequency </Th> <Th> Photon energy </Th> </Tr> <Tr> <Td> Violet </Td> <Td> 380--450 nm </Td> <Td> 668--789 THz </Td> <Td> 2.75--3.26 eV </Td> </Tr> <Tr> <Td> Blue </Td> <Td> 450--495 nm </Td> <Td> 606--668 THz </Td> <Td> 2.50--2.75 eV </Td> </Tr> <Tr> <Td> Green </Td> <Td> 495--570 nm </Td> <Td> 526--606 THz </Td> <Td> 2.17--2.50 eV </Td> </Tr> <Tr> <Td> Yellow </Td> <Td> 570--590 nm </Td> <Td> 508--526 THz </Td> <Td> 2.10--2.17 eV </Td> </Tr> <Tr> <Td> Orange </Td> <Td> 590--620 nm </Td> <Td> 484--508 THz </Td> <Td> 2.00--2.10 eV </Td> </Tr> <Tr> <Td> Red </Td> <Td> 620--750 nm </Td> <Td> 400--484 THz </Td> <Td> 1.65--2.00 eV </Td> </Tr> </Table> <Tr> <Th> Color </Th> <Th> Wavelength </Th> <Th> Frequency </Th> <Th> Photon energy </Th> </Tr>

The longest wavelengths in the visible spectrum are