Red (color)

Physical characteristics

In optical terms, red corresponds to light with comparatively long wavelengths, typically described as roughly 620–750 nanometres; definitions vary slightly by source, so consult scientific references such as those about wavelength for precise boundaries. Human color vision detects red primarily through the long-wavelength-sensitive cone cells in the eye.

Color systems and primaries

How red is treated depends on the color model. In additive color mixing (light), red is one of the primaries alongside green and blue. In many traditional artistic pigment systems, red is grouped with other basic pigments: historically the painter's or subtractive primaries are red, blue and yellow, and more modern print systems use cyan, magenta and yellow. See broader discussions of primary colors for context.

History and pigments

Red pigments and dyes have been important across cultures. Early people used natural earths like red ochre; later, mineral and organic sources such as cinnabar, vermilion, kermes and cochineal produced brighter reds prized in art and textiles. The development of synthetic dyes and pigments in the 19th century expanded the range and permanence of reds available to artists and manufacturers.

Uses and symbolism

Red has diverse practical and symbolic roles. It is widely used for warnings and stop signals (traffic lights and signs), in flags and heraldry, and in design to attract attention. Culturally, red frequently symbolizes love, danger, power, or sacrifice; meanings vary by tradition and context.

Variations and notable facts

• Shades: scarlet, crimson, vermilion and burgundy are common named varieties.
• Contrast with other color systems: the same word “red” can refer to different spectral or pigmentive hues.
• Biology: red coloration in animals can arise from pigments or physical structures that reflect long wavelengths.

Taken together, red is both a specific physical band of visible light and a broad category of cultural and material uses. For more technical or historical detail consult specialist sources and color theory references.