Light is made up of electromagnetic radiation that travels in waves. The wavelength of light determines its color. The wavelength is the distance between consecutive peak points of a wave. Visible light is the light that can be detected by the human eye, and ranges in wavelength from about 400 nanometers (violet) to 700 nanometers (red).
Wavelengths of visible light
The visible light spectrum can be divided into the following colors and wavelength ranges:
| Color | Wavelength range (nm) |
|---|---|
| Violet | 380-450 |
| Blue | 450-495 |
| Green | 495-570 |
| Yellow | 570-590 |
| Orange | 590-620 |
| Red | 620-750 |
As seen in the table, red light has wavelengths ranging from about 620-750 nanometers. Orange light has slightly shorter wavelengths, ranging from approximately 590-620 nm.
Properties of red and orange light
Red and orange light have the longest visible wavelengths. Longer wavelength light has lower energy and frequency than short wavelength light. Violet and blue light have the shortest wavelengths and the most energy.
When white light passes through a prism, the different wavelengths separate into a rainbow spectrum ordered by wavelength. Red light bends the least while passing through the prism, while violet light bends the most. This dispersion occurs because each wavelength travels at a slightly different speed through the prism material.
The red end of the visible spectrum borders on infrared radiation, which has wavelengths longer than red light. Infrared is invisible to human eyes but can be felt as heat. Orange light lies between red and yellow in the spectrum. It is a mix of the long red wavelengths and shorter yellow wavelengths.
Perception of red and orange
The human eye contains photoreceptor cells called cones that are specialized to detect different wavelengths of light. There are three types of cones: S cones, M cones, and L cones. L cones are most sensitive to long red wavelengths. M cones detect green and yellow light. S cones are mainly sensitive to shorter blue wavelengths.
When red light hits the retina, it primarily stimulates the L cones. This cone stimulation produces the perception of the color red in the brain. When orange light strikes the eye, it stimulates both the L and M cones moderately. The brain combines these signals to produce the sensation of orange.
Red and orange are located at the low frequency end of the visible spectrum. As a result, these colors often appear warmer and more energetic to human vision compared to shorter wavelength cool colors like blue and violet.
Uses of red and orange light
The unique properties of red and orange light lend themselves to a number of practical uses:
- Red light does not scatter as easily as short wavelength light, allowing it to penetrate deeper into tissues. Red LEDs are used in phototherapy to heal skin conditions.
- Orange sodium street lamps provide long-wavelength lighting that does not substantially interfere with astronomical observations.
- Red light is often used for brake lamps, turn signals, and traffic lights due to its high visibility compared to other colors.
- Red light is common in plant growth lamps since chlorophyll reflects red and blue light.
- Red and orange are frequently used colors in advertising to grab attention and stimulate appetite.
Interesting facts about red and orange
- The red pigment hemoglobin in blood gives it a red color. Oxygenated blood is bright red while deoxygenated blood is darker red.
- There is evidence that bulls are actually colorblind to red and cannot be angered by it despite the common myth.
- Red light shifts circadian rhythms the least, making it ideal for areas where people work at night.
- In lighting, orange is a mix of red and yellow wavelengths, but in paints and pigments orange is a separate spectral color.
- Red and orange are considered warm colors while blue and violet are seen as cool colors.
- Sunsets often appear reddish and orange due to the scattering of short wavelength blue light in the atmosphere.
Conclusion
In summary, red light has wavelengths from around 620-750 nm and orange has slightly shorter wavelengths from 590-620 nm. These long wavelength colors sit next to each other at the red end of the visible spectrum. Red and orange light stimulate the retina’s L and M cones to produce the perception of these warm colors. Knowing the wavelength ranges and properties of red and orange light helps explain their role in nature, technology, and human vision.
