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I. Properties of Light

Before delving into the details of solar physics, it is important to understand the nature of light. This section will help "illuminate" the behavior of light and show how different types of light are classified and measured. Photons, quantum particles (see “Basics of Quantum Theory”) of energy, travel at the well-known speed c, the speed of light, which is approximately 3 x 108 meters per second. These light particles from the sun, which are constantly bombarding the earth, are characterized on the individual level by their associated frequency or wavelength and therefore their energy (which is given by the frequency/wavelength). An important aspect of light in solar research that will be discussed in this section is intensity or radiant power density, to which there are a few contributing factors that will also be discussed:

  • Photon energy/power – to provide information about how much energy is provided by individual photons.
  • Photon flux – to provide information about just how many photons are coming into contact with our solar cells.
  • Spectral irradiance – to provide information about which types of photons are being received the most and the least.


Pictured above is a prism, an object which separates visible light into its various wavelengths (colors) through a process called refraction.

Source: April 20, 2012.