UVA and tetrachromats
Birds use UVA in the way that they view the world. This is called Tetrachromacy, this is the term used to describe the addition of the all important fourth cone cell in the eye of birds, reptiles and some fish. The inclusion of these four cone shaped cells and the oil droplets that they contain effectively opens up a whole new world to tetrachomats. Humans using three rod cells (trichromacy) can only reportedly view the world with around one million colours. Tetrachromats are able to see around 100 million colours. The inclusion of this fourth cone cell allows the bird to see wavelengths of light that humans simply cannot see i.e far into red and blue and also into the ultra violet wavelength.
UVA is described as the wavelengths of light ranging between 320nm and 400nms. This wavelength is not short enough to start the D3 cycle on its own but has many other reported positive effects in and around birds and reptiles. A balanced natural provision of the correct UVA wavelengths will not only allow the animal to view the world in a more natural way but has been linked to a better feeding response, a more constructive social behavioural pattern and is now also starting to be linked to the production of certain hormones and chemical responses in the brain. A fully illuminated photoperiod including UVA has also been shown to aid in beneficial preening and daily cleaning.
It is vital that we do not confuse full spectrum lamps that have a pleasing natural daylight colour with UV emitting full spectrum lamps; they are totally different!!