Bulls, for instance, cannot see the red color of the cape of a bullfighter, but they are agitated by its movement. Primates can distinguish the full range of the colors of the spectrum visible to humans, but many kinds of mammals, such as dogs and cattle, have dichromacy, which means they can see blues and yellows, but cannot distinguish red and green (both are seen as gray). In the language of optics, red is the color evoked by light that stimulates neither the S or the M (short and medium wavelength) cone cells of the retina, combined with a fading stimulation of the L (long-wavelength) cone cells. It is a primary color in the RGB color model and the light just past this range is called infrared, or below red, and cannot be seen by human eyes, although it can be sensed as heat.

The human eye sees red when it looks at light with a wavelength between approximately 625 and 740 nanometers. They charge the matador's cape because of its motion, not its color. : 39–63īulls, like dogs and many other animals, have dichromacy, which means they cannot distinguish the color red. In China, India and many other Asian countries it is the color symbolizing happiness and good fortune. Modern surveys in Europe and the United States show red is also the color most commonly associated with heat, activity, passion, sexuality, anger, love, and joy. Since red is the color of blood, it has historically been associated with sacrifice, danger, and courage.

Red became a symbolic color of communism Soviet Russia adopted a red flag following the Bolshevik Revolution in 1917, later followed by China, Vietnam, and other communist countries. The 19th century brought the introduction of the first synthetic red dyes, which replaced the traditional dyes. : 60–61 In the Renaissance, the brilliant red costumes for the nobility and wealthy were dyed with kermes and cochineal. It was also an important color in China, where it was used to color early pottery and later the gates and walls of palaces. The Ancient Egyptians and Mayans colored their faces red in ceremonies Roman generals had their bodies colored red to celebrate victories. Red pigment made from ochre was one of the first colors used in prehistoric art. Reds range from the brilliant yellow-tinged scarlet and vermillion to bluish-red crimson, and vary in shade from the pale red pink to the dark red burgundy. It is a primary color in the RGB color model and a secondary color (made from magenta and yellow) in the CMYK color model, and is the complementary color of cyan. It has a dominant wavelength of approximately 625–740 nanometres.

Red is the color at the long wavelength end of the visible spectrum of light, next to orange and opposite violet.

Red light center layouts