The visible spectrum of light refers to the range of colors that the human eye is able to see. The spectrum of visible light consists of 7 main colors: red, orange, yellow, green, blue, indigo, and violet. These 7 colors create the rainbow that we are all familiar with. Each color has a different wavelength and frequency that our eyes can detect. Understanding the spectrum of visible light and the 7 main colors that make it up helps explain how we see color.
The Electromagnetic Spectrum
Visible light is part of the full electromagnetic spectrum. The electromagnetic spectrum encompasses all wavelengths and frequencies of electromagnetic radiation. It ranges from radio waves on the long wavelength and low frequency end, to gamma rays on the short wavelength and high frequency end. Visible light sits between infrared light and ultraviolet light on the electromagnetic spectrum.
The wavelengths and frequencies of the full electromagnetic spectrum are all traveling at the speed of light, but have different properties based on their wavelength and frequency. Longer wavelengths and lower frequencies (like radio waves) can diffract around large objects. Shorter wavelengths and higher frequencies (like x-rays) have more energy and can penetrate objects.
Visible light is the piece of the spectrum our eyes can detect. The small range of visible light wavelengths stimulate the retina in our eyes, allowing us to see color.
The Visible Light Spectrum
The visible light spectrum runs from approximately 380 nanometers to 740 nanometers wavelength. As discussed above, it sits between infrared light (longer wavelength) and ultraviolet light (shorter wavelength).
Within the visible light spectrum, the wavelengths and frequencies correspond to the 7 main colors as follows:
| Color | Wavelength Range (nm) | Frequency Range (THz) |
|---|---|---|
| Red | 620-750 | 400-484 |
| Orange | 590-620 | 484-508 |
| Yellow | 570-590 | 508-526 |
| Green | 495-570 | 526-606 |
| Blue | 450-495 | 606-668 |
| Indigo | 445-450 | 668-699 |
| Violet | 380-445 | 699-789 |
As seen in the table, red light has the longest wavelengths within the visible spectrum, while violet light has the shortest wavelengths. The longer wavelength red light has lower frequency, while the shorter wavelength violet light has higher frequency. The other colors fall between red and violet in terms of their wavelength and frequency.
Our eyes detect these wavelengths as varying colors. When all the wavelengths of the visible spectrum enter our eye at full intensity, we perceive this as white light. The visible spectrum of light accounts for all the possible colors our eyes can detect in nature.
Properties of the 7 Colors
Each color in the visible light spectrum has specific properties and characteristics:
Red
– Longest wavelength visible light
– Lowest frequency visible light
– Wavelength range = 620-750nm
– Frequency range = 400-484THz
Red has the longest wavelength and lowest frequency of the visible spectrum. It therefore has the least energy. Red light elicits a strong physiological reaction in humans, increasing heart rate and stimulating faster breathing. Red light also enhances visibility in haze or fog.
Orange
– Medium-long wavelength visible light
– Medium-low frequency visible light
– Wavelength range = 590-620nm
– Frequency range = 484-508THz
Orange is a mix of red and yellow light. Orange light also stimulates physiological reactions, though less strongly than red light. It has better visibility in fog than yellow or green light.
Yellow
– Medium wavelength visible light
– Medium frequency visible light
– Wavelength range = 570-590nm
– Frequency range = 508-526THz
Yellow sits in the middle of the visible light spectrum in terms of wavelength and frequency. Of all the colors, yellow has the strongest visibility in fog or haze. It also has strong luminance against a white background. Yellow elicits feelings of optimism and warmth in human observers.
Green
– Medium-short wavelength visible light
– Medium-high frequency visible light
– Wavelength range = 495-570nm
– Frequency range = 526-606THz
Green is at the center of the visible spectrum. It is considered the most restful color for human eyes. Green light is effective for enhancing visibility at night because the human eye is most sensitive to green.
Blue
– Shorter wavelength visible light
– Higher frequency visible light
– Wavelength range = 450-495nm
– Frequency range = 606-668THz
Blue has a shorter wavelength and higher frequency than the other visible colors. Blue light scatters more in the atmosphere, causing the sky to appear blue. Blue connotes feelings such as calmness and stability. However, exposure to too much blue light at night can disrupt human circadian rhythms.
Indigo
– Very short wavelength visible light
– Very high frequency visible light
– Wavelength range = 445-450nm
– Frequency range = 668-699THz
Indigo is a dark blue color close to violet on the spectrum. Natural indigo in light is hard to discern, leading some to say it is not a distinct color in the spectrum. However, it is considered one of the 7 traditional colors of the rainbow.
Violet
– Shortest wavelength visible light
– Highest frequency visible light
– Wavelength range = 380-445nm
– Frequency range = 699-789THz
Violet has the shortest wavelengths and highest frequencies of visible light. Like blue light, violet has high scattering in the atmosphere. Violet is at the lower end of human visual sensitivity and therefore appears darker than other colors. Ultraviolet light, just beyond violet, is invisible to the human eye.
Perception of Color
The perception of color in these 7 bands of the visible spectrum depends on the cone cells in our eyes. There are three types of cone cells, each sensitive to different wavelengths of light:
– Short wavelength cones – Most sensitive to blue/violet light
– Medium wavelength cones – Most sensitive to green light
– Long wavelength cones – Most sensitive to red light
These cone cells have peak sensitivities that roughly align with blue, green, and red light on the visible spectrum. All other colors we perceive are combinations of signals from these three cone types. For example, yellow activates both the medium and long wavelength cones. This is why there are no single cone cells sensitive to yellow, orange, indigo, etc. Our brain combines the cone cell responses to generate all color perceptions.
Additive Color Mixing
When combining colored light, the colors add together to generate new perceptions. This is known as additive color mixing, and underlies how our eyes see all colors in the visible spectrum:
– Red + Green = Yellow
– Red + Blue = Magenta
– Green + Blue = Cyan
– Red + Green + Blue = White
With additive mixing, combining all colors at full intensity gives white light. This is because the full visible spectrum entering our eyes is perceived as complete white light. Televisions and other screens create color through combinations of red, green, and blue light. Additive color mixing of light underlies the range of visible colors we can experience.
The Visible Spectrum in Nature
We can observe the full visible light spectrum in natural rainbows. As white sunlight passes through rain drops, the different colors in the spectrum bend at slightly different angles, spreading them out in an arc. The wavelengths of visible light align with the 7 color bands, creating the rainbow.
We can also see the spectrum in soap bubbles, oil slicks, prisms, and other effects. The range of possible colors we see derive from the 7 bands of visible light. Other animals can see different wavelength ranges, expanding or shifting the visible spectrum. But for human vision, these 7 colors define all that our eyes can perceive.
Conclusion
The visible spectrum derived from electromagnetic radiation encompasses the 7 main color bands detectable by human vision: red, orange, yellow, green, blue, indigo, and violet. These colors have specific wavelength ranges and frequencies. The properties of each color band contribute to its visual effects and perception.
The visible spectrum spans a small segment of the full electromagnetic spectrum. But within this range, the 7 color bands compose all the colors we can see in nature. Understanding the spectrum provides insight into how our eyes detect light and perceive color in the world around us.