red

Red is a color at the long-wavelength end of the visible spectrum, roughly 620 to 750 nanometers. Humans perceive red when light within this range stimulates the L-cone photoreceptors in the retina.

In additive color systems used for light, red is a primary color alongside green and blue. In traditional pigment mixing (RYB model), red is treated as a primary color; in modern printing (CMYK), red is produced by combining magenta and yellow.

Red is often associated with warmth, energy, and intensity; culturally, it can signify danger or warning (stop signs), love and passion, or luck in various societies.

Red is widely used in art, design, branding, and signage to attract attention and convey emphasis.

Historically important red pigments include vermilion and cadmium red; natural dyes include cochineal (carmine) and madder. Modern pigments include synthetic organic and inorganic reds.