Red is a color that exists at the end of the visible spectrum, next to orange and opposite violet. It has a dominant wavelength range of approximately 625–740 nanometers. The exact hue range that defines “red” can vary depending on the color system used. Here’s a closer look at the hue range of red across different color models and systems.
The Visible Spectrum
The visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye. The wavelengths of light in the visible spectrum range from about 380 to 740 nanometers (nm). Red sits at the long wavelength end of the visible spectrum, next to orange:
- Violet: ~380-450 nm
- Blue: 450-495 nm
- Green: 495-570 nm
- Yellow: 570-590 nm
- Orange: 590-625 nm
- Red: ~625-740 nm
Within the visible spectrum, red light has the longest wavelengths and the lowest frequencies. When all wavelengths of the visible spectrum are combined, white light is produced. The dominant wavelength of red light is approximately 625-740 nm.
The CIE 1931 Color Space
One of the first mathematically defined color spaces was developed by the International Commission on Illumination (CIE) in 1931. The CIE 1931 color space represents colors using the x and y chromaticity coordinates. The boundaries of red in the CIE 1931 color space are approximately:
- x: 0.44 to 0.71
- y: 0.29 to 0.51
On the CIE 1931 chromaticity diagram, red hues occupy the curved region towards the bottom right. The dominate wavelength of red is around 700 nm in this color space.
RGB Color Model
The RGB color model is used for colors displayed on electronic devices like TVs, computers, and phones. In the RGB model, red is created by combining high intensities of the red channel with low intensities of the green and blue channels.
In 8-bit RGB with integer values from 0-255, the range for red is approximately:
- Red: 150-255
- Green: 0-100
- Blue: 0-100
In hexadecimal RGB triplets, the range is #A00000 to #FF0000. The dominant RGB values for red hues are #FF0000 to #FF5F5F.
HSV/HSB Color Model
The HSV (hue, saturation, value) model defines colors using hue, saturation, and value attributes. Hue represents the dominant wavelength, saturation describes the vibrancy, and value sets the brightness.
In the HSV cone, red hues occupy the bottom right region. The hue range for red is approximately:
- Hue: 0 to 22°
- Saturation: 75% to 100%
- Value: 50% to 100%
The dominant red hues have a hue angle of around 0°.
Pantone Colors
Pantone is a proprietary color system used in design, printing and manufacturing. It defines standardized pigments for accurate color reproduction. Some examples of red Pantone colors and their hue values are:
| Pantone Color | Hue Angle |
|---|---|
| Pantone Warm Red C | 13° |
| Pantone Bright Red C | 14° |
| Pantone Rhodamine Red C | 20° |
| Pantone Rubine Red C | 348° |
As shown, red Pantone colors span a hue range of about 13-20° in the HSV model. The exact hue depends on the shade and tint.
Natural Red Pigments
In nature, red color comes from pigments in plants, minerals and animals. Here are some examples of natural red pigments and their source:
- Lycopine – Found in tomatoes and red fruits.
- Astaxanthin – Found in algae, krill, lobster shells.
- Anthocyanins – Water-soluble pigments in red berries and wine.
- Hemoglobin – Oxygen-carrying protein in red blood cells.
- Carmine – Pigment from cochineal beetles.
- Cinnabar – Mercury sulfide mineral.
These natural red pigments absorb green and blue light while reflecting more red wavelengths, giving them their distinctive red hues.
Cultural Meanings of Red
Red carries strong cultural symbolism and meanings in many societies. Here are some common associations with red color:
- Danger, warnings
- Energy, excitement
- Passion, desire, love
- Heat, fire
- Aggression, intensity
- Importance, power
- Courage, bravery
- Celebration, festivals
Red evokes strong emotions and reactions due to its prominence at the visible spectrum. It has one of the longest wavelengths detectable by the human eye.
History and Etymology of Red
The word “red” has been part of the English language for over 1000 years. Here are some notes on the origins and history of the word:
- Derived from Old English “read”
- Cognate with other Germanic terms like German “rot”
- Comes from Proto-Germanic “rauthaz”
- Related to words like “rust”, “ruby”, “ruddy”
- Ancient roots from Proto-Indo-European base “hreudh-” meaning red
In many languages, the word for “red” is derived from the color of blood, wine, or rust oxidation. Some scholars link it to the rosy glow of health and life.
Conclusion
Red occupies the long wavelength end of the visible light spectrum. Its exact hue range varies across color spaces, but overall it spans 625-740 nanometers. Red primarily stimulates the L cone cells in the eye responsible for long wavelength detection. It evokes strong reactions and symbolism across cultures. The richness of red derives from its prominence at the edge of human vision, making it an impactful and culturally significant color.