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Does the color or hue of light depends on its wavelength?

The color or hue of light is determined by its wavelength. Light is part of the electromagnetic spectrum, which includes radio waves, microwaves, infrared radiation, visible light, ultraviolet rays, x-rays and gamma rays. Of these, visible light constitutes a very small range from approximately 380 to 750 nanometers. The specific wavelength of light determines what color our eyes perceive it to be.

The Electromagnetic Spectrum

The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation. Electromagnetic radiation is energy that travels and spreads out as it goes. The electromagnetic spectrum ranges from very long radio waves to very short gamma rays. It encompasses all the frequencies of electromagnetic energy from below the frequencies of radio waves to above the frequencies of gamma rays. Radiation with frequencies above the electromagnetic spectrum are called ionizing radiation because they have enough energy to ionize atoms and molecules and break chemical bonds.

The electromagnetic waves in the electromagnetic spectrum vary in size from very long radio waves the size of buildings, to very short gamma rays smaller than the size of the nucleus of an atom. In general, gamma rays have the highest frequency and energy, and radio waves have the lowest frequency and energy. From highest to lowest frequency and energy, the waves of the electromagnetic spectrum are:

  • Gamma rays
  • X-rays
  • Ultraviolet
  • Visible light
  • Infrared
  • Microwaves
  • Radio waves

The only electromagnetic waves we can actually see are visible light waves. The human eye can only detect the wavelengths that correspond to the colors of the rainbow. All the other wavelengths are invisible to the human eye.

Properties of Electromagnetic Waves

All electromagnetic waves have the same basic properties and travel through space at the speed of light. The differences between the various types of electromagnetic waves come from the energy and frequency they possess. The energy of an electromagnetic wave is directly related to its frequency, and is inversely related to its wavelength. In other words, high frequency electromagnetic waves have high energy and short wavelengths. Low frequency waves have low energy and long wavelengths.

Some key properties of electromagnetic waves:

  • Speed of propagation – All electromagnetic waves travel at the speed of light in a vacuum, which is about 300,000,000 meters per second or 670,616,629 miles per hour.
  • Wavelength – The distance between corresponding points of two adjacent waves. Wavelengths range from kilometers to picometers.
  • Frequency – The number of wave oscillations that pass a point per unit of time. Frequency is measured in Hertz. High frequency equals short wavelength.
  • Energy – Electromagnetic waves carry energy as they propagate through space. Higher frequency waves have higher energy.

The Visible Light Spectrum

As mentioned previously, visible light is the very small portion of the electromagnetic spectrum that human eyes can detect. Visible light ranges in wavelength from approximately 380 nanometers to 750 nanometers. A nanometer is one billionth of a meter. Other wavelengths of electromagnetic radiation outside this narrow range of visible light are invisible to humans. They include radio waves, microwaves, infrared radiation, ultraviolet rays, x-rays and gamma rays.

The color of visible light depends on its wavelength. Shorter wavelengths are bluish and longer wavelengths are reddish. The visible spectrum of light can be remember by a common mnemonic ROYGBIV:

  • R – Red light has the longest wavelength visible to humans, around 700 nm.
  • O – Orange light has a wavelength of approximately 620-580 nm.
  • Y – Yellow light has a wavelength of roughly 580-550 nm.
  • G – Green light has a wavelength of about 550-495 nm.
  • B – Blue light has a wavelength of around 495-450 nm.
  • I – Indigo light has a wavelength of approximately 450-425 nm.
  • V – Violet light has the shortest wavelength that human eyes can see, roughly 425-400 nm.

So in summary, red light with the longest wavelength appears at one end of the visible spectrum, while violet light with the shortest wavelength is at the other end. The other colors fall in between at various wavelengths. This range of wavelengths that human eyes perceive as color is quite narrow compared to the entire electromagnetic spectrum.

Wavelength and Frequency

Wavelength and frequency are intrinsically related to one another. Wavelength is measured in distance, such as meters, while frequency is measured in occurrences over time, such as Hertz or cycles per second. The higher the frequency of a wave, the shorter the wavelength. The shorter the wavelength, the higher the frequency.

The wavelength (λ) of an electromagnetic wave is related to its frequency (f) and the speed of light (c) by the equation:

c = λf

Where c is a constant (speed of light = 300,000,000 m/s). So if you know any two of the values, you can calculate the third one using this equation. For example, red light with a wavelength of 700 nm has a frequency of 428 THz (428,000,000,000 Hz). Higher frequency light has a shorter corresponding wavelength.

Energy of Photons

Not only do different wavelengths of light relate to color, but they also correspond to the energy carried. Light energy is carried in discrete packets called photons. Photons carry levels of energy proportional to the radiation frequency. High frequency photons have higher energy, while low frequency photons have lower energy. This results in high frequency ultraviolet light being able to damage DNA, while low frequency radio waves have very low energy and pass harmlessly through our bodies.

The energy of a photon can be calculated using the Planck-Einstein relation:

E = hf

Where E is the energy of the photon, h is Planck’s constant, and f is the frequency of the radiation.

Therefore, by knowing the frequency or wavelength of electromagnetic radiation, you can derive the other properties such as energy. This demonstrates the intrinsic relationship between the properties of light across the electromagnetic spectrum.

Perception of Color

The human eye contains receptor cells called cones that respond to different wavelengths of light. There are three types of cones:

  • S cones – Respond to short blue wavelengths of light
  • M cones – Respond to medium green wavelengths
  • L cones – Respond to longer red wavelengths

These cones send signals to the brain based on how much they are stimulated by incoming light. The brain interprets these signals as color. For example, red light strongly stimulates the L cones but only weakly stimulates the S and M cones. The brain interprets this input combination from the cones as the color red.

The visible spectrum of light that stimulates the three types of cones in varying degrees accounts for all the colors we see. So in summary, color is our visual perception of different wavelengths of visible light.

Other Properties of Light

In addition to wavelength, frequency and energy, light can be characterized by other properties including:

  • Brightness – Perception elicited by the luminance or intensity of light. Related to the amplitude of a wave.
  • Reflection and Refraction – Light bounces off surfaces at an angle equal to the incoming angle. Light bends when passing between materials.
  • Diffraction – Bending waves around an opening or obstacle. Causes light to spread out.
  • Polarization – Restricting the direction of vibration to one plane. Can filter and block light.

So in summary, many properties can characterize light, but the most fundamental one that determines color is wavelength.

Conclusion

In conclusion, wavelength determines the color or hue of visible light. Light is part of the electromagnetic spectrum which ranges from long radio waves to short gamma rays. Of this spectrum, humans can only see visible light between 380-750 nanometers wavelength. Shorter wavelengths are perceived as violet and blue, while longer wavelengths appear red. Frequency is intrinsically related to wavelength, with higher frequency light having a shorter corresponding wavelength. In addition to color, wavelength also determines other light properties like energy. Different wavelengths stimulate the eye’s cone cells differently, which the brain interprets as color. So the bottom line is that wavelength fundamentally determines the color or hue of visible light.

Color Wavelength Range
Red ~700 nm
Orange ~620-580 nm
Yellow ~580-550 nm
Green ~550-495 nm
Blue ~495-450 nm
Indigo ~450-425 nm
Violet ~425-400 nm