Welcome readers! In this post, we’ll examine the frequencies of visible light colors and determine which has the lowest frequency. Light can be described as an electromagnetic wave, with different frequencies corresponding to different colors. The frequency of light determines its position on the visible spectrum. Let’s explore the EM spectrum and color frequencies in more detail.
The Visible Spectrum
The visible spectrum is the portion of the full electromagnetic (EM) spectrum that is visible to the human eye. The EM spectrum encompasses all electromagnetic radiation, from radio waves to gamma rays. Humans can only see wavelengths in the range of approximately 380-700 nanometers (nm). This range is known as the visible spectrum.
The visible colors we perceive correspond to different wavelengths within this range. Red has the longest wavelength at ~700nm while violet has the shortest at ~380nm. In between we have orange, yellow, green, blue, and indigo. Shorter wavelengths are higher frequency while longer wavelengths are lower frequency. So violet light is the highest frequency we can see and red is the lowest.
To understand which color has the lowest frequency, we first need to understand how frequency is measured. Frequency refers to the number of wave cycles that pass a fixed point per unit of time. It is typically measured in hertz (Hz), which is equal to one cycle per second.
The frequency of electromagnetic waves is related to their wavelength by this basic equation:
Frequency (Hz) = Speed of light (m/s) / Wavelength (m)
Since the speed of light in a vacuum is a constant (~3 x 108 m/s), shorter wavelengths will have higher frequencies, while longer wavelengths will have lower frequencies.
Visible Light Frequencies
Using the above equation, we can calculate the frequencies for visible light colors:
|7.89 x 1014
|6.67 x 1014
|5.88 x 1014
|5.26 x 1014
|5.08 x 1014
|4.29 x 1014
This table shows the frequencies of the visible spectrum colors in hertz. As we can see, violet light has the highest frequency at ~7.9 x 1014 Hz, while red has the lowest frequency at ~4.3 x 1014 Hz.
The Red End of the Spectrum
Red light is at the long wavelength, low frequency end of the visible spectrum. The specific frequency of red that our eyes perceive as the color red is around 4.29 x 1014 Hz.
However, there are electromagnetic waves with even longer wavelengths and lower frequencies than red light. They are simply outside the visible range. For example:
- Microwaves – ~1 GHz to 300 GHz
- Radio waves – 3 kHz to 300 GHz
- Infrared – 300 GHz to 400 THz
These types of lower frequency radiation are used for radio transmission, thermal imaging, microwave ovens, and other technologies. But they are invisible to our eyes. Red visible light represents the lowest frequency we can visually detect.
Perception of Color
Our eyes contain special receptor cells called cones that are sensitive to different light wavelengths. There are three types of cones activated by long (L), medium (M), and short (S) wavelength light. The combination of signals from these cones allows us to perceive color.
The L cones are activated by reddish light in the long wavelength end of the visible spectrum. The maximum absorption peak for L cones corresponds almost exactly with the ~700 nm wavelength we call red. So our perception of red light aligns with the lowest frequency band of visible light.
Properties of Red Light
The fact that red is the lowest frequency visible light color also imparts some unique properties:
- Red light is scattered least by the atmosphere, allowing it to travel long distances which makes red sunsets prominent.
- Longer red wavelengths penetrate tissue well, which is why red light is used in medical therapies.
- Red has the lowest photon energy of visible light. This can influence chemical reactions responsive to light.
So the physical and biological effects of light can depend on its frequency spectrum. Red sits at the low energy, low frequency end of visibility.
Beyond Visible Frequencies
While red may have the lowest frequency that our eyes detect, there are many types of electromagnetic radiation at frequencies below red light. They include (in order of decreasing frequency):
|300 GHz – 400 THz
|1 GHz – 300 GHz
|3 kHz – 300 GHz
Of these, the lowest frequencies detectable are certain radio waves at around 3 kHz. That is over a quadrillion times lower frequency than visible red light! Radio technology allows us to harness electromagnetic waves far below what our eyes can see.
In summary, red light sits at the low frequency end of the visible spectrum with a frequency of around 4.29 x 1014 Hz. While many colors have higher frequencies than red, it represents the lowest frequency visible to human eyes. But there are many types of electromagnetic radiation extending to vastly lower frequencies that we cannot see, such as radio waves. Understanding the electromagnetic spectrum and light frequencies helps explain the behavior of different colors and non-visible radiation.
So when considering which color has the lowest frequency, the answer is red! Its long wavelength of ~700 nm corresponds to a frequency of ~4.29 x 1014 Hz, defining the lower boundary of the visible light spectrum. While many interesting electromagnetic phenomena occur at frequencies below this, red light marks the lowest frequency we can actually see with our eyes.