Solar light 1

Referencing:
- ET3034Tux - 1.6.1 – Solar light 1, https://www.youtube.com/watch?v=lDYFtO9QxsM
- www.google.com

Light is dual natured: it can be described as electromagnetic waves, or as particles which have quantised amounts of energy, called photons.  The photoelectric effect shows that electrons can be ejected from a material upon light absorption by the material.  This ejection requires light with a certain threshold energy, which arises from a material-dependent threshold frequency.  Energies and frequencies below this threshold will not cause electrons to be ejected.  This is shown by the formula for light energy:

E = hv

where h is Planck's constant, and v is the frequency of the incident light.

As an electromagnetic wave, light can be described as propagating in a particular direction.  Perpendicular to this direction, an electric field oscillates in a plane.  Perpendicular to this direction and the plane of the electric field, a magnetic field oscillates.  The distance between the maxima of the electric field's oscillation is called the wavelength λ.  The speed of the light's propagation in vacuum is c.  These are related to the frequency of light by this equation:

c = λv

Hence: E = hv = hc/λ

Irradiance I (also known as solar irradiance, power density or radiant power density) is the power of light per unit area, with units watts per square metre.  The spectral power density P is a quantity with spectral information because it is the incident power of light per unit area per unit wavelength.  I and P are related by this equation:

I = ∫₀^λ P(λ) dλ