How much power is contained in a beam of light? (Intermediate)

Hello, i am a curious person just trying to learn more, just wondering how much power is in a beam of light? not laser or anything like that just an ordinary everyday beam of light say from the Sun.

The power in a beam of light depends on (a) the wavelength of the light (which determines the energy) and (b) the number of packets of energy that come in the beam per second. So fundamentally the amount of energy is dependent on the source of the light. In the case of the Sun, the power reaching the Earth (as both light and heat) is about 1400 Watts per square meter, which means that each place on Earth with an area of 1 square meter collects 1400 Watts.

Outside of the standard colors ROYGBIV, does a beam of light theoreticaly hide waves inside like say radio waves or do the waves have air between them or are they continous where one stops the other begins,what im asking i guess is we have learned to harness a beam of light that is concentrated to do many wonderful things and some not so wonderful but what would happen if the other way was taken, you know that simple area where manipulations can occur without the absolute use of force, like in the movie predator, and yes i know it was just a movie, but the monster used something to manipulate light where it bends around instead of cuts through, something like that.

This is a little complicated: light behaves as a particle and as a wave. This applies even to standard colors roygbiv. Light is essentially an electromagnetic wave which consists of oscillating electric and magnetic fields. You know that a magnetic field (or an electric field) will exist even in vacuum if you place a magnet in space. So, an electromagnetic wave does not need air or any medium to propagate.

The frequency of the oscillations of these fields determines the "color" of the light. Radio waves are electromagnetic waves which have a low frequency (i.e. the number of oscillations of the fields per second is relatively small). Our eyes are sensitive to certain specific frequencies and that is what we "see" in our day to day life. Red light has the lowest frequency and blue light has the highest frequency. Frequencies higher than blue light are invisible to our eyes and exist as ultraviolet light, X-rays and gamma rays. So, there is no gap where radio waves end and visible light begins. It is all one continuous spectrum.

Now, waves can be made to interfere with each other and that causes the wave properties of light (like interference, diffraction, etc.). So, when light passes through a narrow opening, instead of forming a sharp pattern on a screen behind the hole, it disperses a little and this is called diffraction. Light can be bent using a medium; this is called refraction and this is what is used in lenses to focus light.

However, light also behaves as a particle. What this means is that light is composed of wave packets, each packet consisting of definite quanta of energy. These quanta are called photons and these behave like particles. This manifests in phenomena like the photoelectric effect.

This page was last updated June 27, 2015.

About the Author

Jagadheep D. Pandian

Jagadheep D. Pandian

Jagadheep built a new receiver for the Arecibo radio telescope that works between 6 and 8 GHz. He studies 6.7 GHz methanol masers in our Galaxy. These masers occur at sites where massive stars are being born. He got his Ph.D from Cornell in January 2007 and was a postdoctoral fellow at the Max Planck Insitute for Radio Astronomy in Germany. After that, he worked at the Institute for Astronomy at the University of Hawaii as the Submillimeter Postdoctoral Fellow. Jagadheep is currently at the Indian Institute of Space Scence and Technology.

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