Examples of Radiant Energy

We explain that what are the examples of radiant energy?The radiant energy is containing all waves of the electromagnetic spectrum , which are:

  • Radio waves
  • TV waves
  • Microwave
  • Infrared rays
  • Visible light (Red, orange, yellow, green, blue, indigo, violet)
  • Ultraviolet rays (A, B)
  • X-rays
  • Gamma Rays (Alpha, Beta)

The electromagnetic spectrum

Also known as the energy spectrum , the electromagnetic spectrum is the set of radiations that make up all radiant energy , that is, the composition of a “non-monochromatic” (of various colors) or composite radiation.

All of these cover frequencies from 10 7 Hertz to 10 24 Hertz. Each type of radiation has a wavelength and a frequency that defines it. From radio waves to visible light they are non-ionizing radiation. From ultraviolet rays to Gamma rays, they are ionizing radiation, that is, when they affect, they separate the matter into the ions that compose them.

Radiation characteristics

The speed at which all waves propagate is equal to that of light:

C = 3×10 8 m / s

And it is determined by the expression:

C = λ * v

Where λ is the wavelength and v is the frequency in the radiation in question.

If the variations of the electric and magnetic fields in a wave can be represented exactly by a single sinusoidal (sinusoidal) function of time t, the wave is said to be monochromatic (of a single color), and is characterized by its frequency v or by their wavelength λ , which are related to each other in the expression:

λ = C / v

Therefore, the only physical characteristic of radiation is the frequency v , since the wavelength λ   depends on the speed, and therefore on the medium in which it propagates. The value of the frequency v is a function of the characteristics and performance of the emitting body.

However, to describe radiation, the wavelength λ is used in a vacuum or in air. Within the electromagnetic spectrum, the range of the visible spectrum (white light) is defined as between λ = 380 nm and λ = 770 nm . This interval is also known as visible light , and it is made up of seven colors: red, orange, yellow, green, blue, indigo, and violet.


The radiometry is the science which aims to measure the radiant energy in general. In order to define the radiometric quantities, it is necessary to know what type of source, be it point or extensive, we are referring to.

source is point when its dimensions are small with respect to the distance that separates it from the observer (a star is always a point source) and a source will be extensive when this does not happen.

source is a surface or volume that emits radiant energy . A source is primary if it is itself that produces the energy, like the stars. The source is secondary if what it does is to resend part of the radiant energy it receives; an example is the moon.

Radiometric quantities

For point sources, the following radiometric quantities have been defined:

  • Radiant energy : energy emitted, transferred or received in the form of electromagnetic waves or photons. It is measured in Joule (J) .
  • Radiant flux: energy emitted, transferred or received in an elementary interval of time divided by the value of said interval. It is measured in watts (W) .
  • Radiant intensity: Radiant flux, emitted or transferred, within a solid angle element with vertex at the point and containing the given direction, divided by the value of said solid angle element. It is measured in watts over steradian (W / sr).

For large sources, the radiant intensity is not applicable, so two different magnitudes are established:

  • Radiant excitance: it refers to a point on a surface, and is the radiant flux emitted by a surface element that contains the point, divided by the area of ​​said surface element. It is useful when you want to know the energy emitted in all directions. It is a surface density of energy flux, and refers to energy emitted. It is measured in watts over square meter (W / m 2 ).
  • Radiance: it refers to a point of a surface and a direction, it is the radiant flux transferred by a surface element that contains the given point, within an elementary solid angle that contains the direction and whose indicator is the limit of the surface element , divided by the area of ​​that surface element and the value of the solid angle. It is useful when you want to measure the energy emitted in a certain direction. It is measured in watts over steradian – square meter (W / sr m 2 ).

There is a radiometric magnitude for surfaces that receive radiant energy : Irradiance . This is defined when it refers to a point on a surface as the radiant flux received by a surface element that contains the point divided by the area of ​​that surface element. It is also a surface density of energy flux, and refers to received energy. It is measured in watts over square meter (W / m 2 ).

Examples of radiant energy

  1. The light emitted by neon gas lamps.
  2. The light we receive reflected by the moon.
  3. The light we receive from the sun.
  4. The light emitted by burning wood in a fireplace.
  5. The light emitted by the wick of a candle when it burns.
  6. X-rays that they strike through the body to create plaques in bone studies.
  7. Radio waves that are emitted by radio towers and received by our devices.
  8. Microwaves that increase the internal kinetic energy of food.
  9. The colored light that arises in the oxidation reactions of elements such as sodium and magnesium, when exposed to a flame.
  10. The ultraviolet rays that come from the sun and filter into the atmosphere.
  11. Gamma rays that spread through the universe.
  12. The television waves that are transmitted through towers and reach the antennas of the homes that still use them.

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