Violet is the color of amethyst, lavender and beautyberries. It takes its name from the violet flower. Violet is the color at the end of the visible spectrum of light between blue and the invisible ultraviolet. Violet color has a predominant light wavelength of roughly 380-450 nanometers (in experiments under special conditions, people have so far seen to 310 nm). Light with a shorter wavelength than violet but longer than X-rays and gamma rays is called ultraviolet. In the color wheel historically used by painters, it is located between blue and purple. On the screens of computer monitors and television sets, a color which looks similar to violet is made, with the RGB color model, by mixing red and blue light, with the blue twice as bright as the red. This is not true violet, since it is composed of multiple longer wavelengths rather than a single wavelength shorter than that of blue light. Violet and purple look very similar; but violet is a true color, with its own set of wavelengths on the spectrum of visible light, while purple is a composite color, made by combining blue and red. In history, violet and purple have long been associated with royalty and majesty. The emperors of Rome wore purple togas, as did the Byzantine emperors. During the Middle Ages violet was worn by bishops and university professors and was often used in art as the color of the robes of the Virgin Mary. According to surveys in Europe and the United States, violet is the color people most often associate with extravagance and individualism, the unconventional, the artificial, and ambiguity. In Chinese painting, the color violet represents the harmony of the universe because it is a combination of red and blue (Yin and yang respectively). In Hinduism and Buddhism violet is associated with the Crown Chakra.