What is the wavelength range of visible light?

Short Answer

The wavelength range of visible light is the part of the electromagnetic spectrum that the human eye can detect. It lies roughly between 400 nanometers (nm) and 700 nanometers (nm). The shorter wavelengths around 400 nm appear violet, while the longer wavelengths around 700 nm appear red.

This wavelength range contains the seven colours of the rainbow—violet, indigo, blue, green, yellow, orange, and red. Visible light is only a small part of the electromagnetic spectrum, but it is extremely important because it allows us to see the world around us.

Detailed Explanation :

Wavelength Range of Visible Light

Visible light is the portion of electromagnetic radiation that can be detected by the human eye. Although the entire electromagnetic spectrum extends from very long radio waves to very short gamma rays, visible light occupies only a narrow band in the middle of this spectrum. This narrow band lies between the wavelengths of approximately 400 nm and 700 nm.

The concept of wavelength range helps us understand how light behaves and how the human eye perceives different colours. The colours that we see in a rainbow or in everyday life are the result of different wavelengths within this visible range.

Understanding Wavelength

Wavelength is the distance between two consecutive crests or troughs of a wave. In the case of visible light:

  • Shorter wavelengths are closer together
  • Longer wavelengths are farther apart

Wavelength determines the colour of the light we see. For example:

  • Light with a shorter wavelength appears violet or blue.
  • Light with a longer wavelength appears orange or red.

Exact Wavelength Range

The approximate boundaries of visible light are:

  • Lower limit: 400 nm (violet)
  • Upper limit: 700 nm (red)

Here, “nm” stands for nanometer, which is one-billionth of a meter.

Colours Found in This Range

Visible light consists of seven main colours, often remembered as VIBGYOR:

  1. Violet (around 400 nm)
  2. Indigo
  3. Blue
  4. Green
  5. Yellow
  6. Orange
  7. Red (around 700 nm)

Each colour corresponds to a specific range of wavelengths. When white light passes through a prism or water droplets, these wavelengths separate, producing a rainbow.

Energy and Wavelength Relationship

Energy of light is inversely related to its wavelength:

  • Shorter wavelengths (violet) have higher energy
  • Longer wavelengths (red) have lower energy

This means violet light carries more energy than red light, even though both are visible to the human eye.

Why the Human Eye Sees Only 400–700 nm

The eye has light-sensitive cells called cones, which respond to the wavelengths in the visible spectrum. These cones are not sensitive to wavelengths shorter than 400 nm (ultraviolet) or longer than 700 nm (infrared). Therefore, we cannot see UV or IR radiation even though they exist.

Interaction of Visible Light With Matter

The wavelength range of visible light determines how it behaves when it interacts with materials:

  • Reflection: Some wavelengths bounce off surfaces and we see that colour.
  • Absorption: Materials absorb certain wavelengths; the remaining wavelengths define the colour seen.
  • Transmission: Transparent materials allow visible wavelengths to pass through.
  • Dispersion: Different wavelengths bend at different angles in a prism, producing spectral colours.

For example, a leaf appears green because it absorbs all other wavelengths and reflects green light.

Role of Visible Light in Daily Life

Visible light in the 400–700 nm range is essential for:

  • Vision — Without this range, we would not see objects or colours.
  • Photosynthesis — Plants use visible light, mainly red and blue wavelengths, to produce food.
  • Communication — Fibre optic cables use visible and near-visible light to transmit data.
  • Safety and signalling — Traffic lights, signs, and screens rely on visible wavelengths.
  • Technology — Cameras, microscopes, projectors, and telescopes work using visible wavelengths.

Scientific Importance of Visible Wavelengths

Understanding the wavelength range is important in science because it helps in:

  • Designing optical instruments
  • Studying the light emitted by stars
  • Identifying chemicals through their light absorption
  • Understanding human vision and colour perception

Visible light plays a key role in astronomy, chemistry, biology, and physics.

Why Visible Light Is Only a Small Part of the Spectrum

The electromagnetic spectrum includes many types of waves, such as radio, microwaves, infrared, ultraviolet, X-rays, and gamma rays. Compared to this huge range, 400–700 nm is a very narrow band. Yet, it is the most familiar to us because our eyes evolved to detect this part of sunlight, which reaches Earth’s surface in large amounts.

Conclusion

The wavelength range of visible light lies between 400 nm and 700 nm, covering the seven colours from violet to red. This range represents the light that human eyes can detect. Although small compared to the entire electromagnetic spectrum, visible light is essential for vision, communication, nature, and technology. Understanding this wavelength range helps explain how colours form, how eyes work, and how light interacts with matter.