Fundamentals of light

In this lesson, we will learn:

• What is light?
• Source of light
• Light is the visible part of electromagnetic waves
• Light range frequencies
• Visible light colors and wavelengths
• Ray model of light
• Solving problems involving the speed of light
• Solving illumination problems

• Light is emitted and reflected from objects around us
• Light is a small visible part of electromagnetic waves.
• Light travel along straight line in vacuum or other uniform medium
• The nature of light is explained by two models; particle model and wave model
• Light frequency changes upon moving along the electromagnetic spectrum
• Light is the range of frequencies of electromagnetic waves
• Light waves have wavelength about 400nm to 700nm
• Shortest wavelengths are seen as violet light
• Longest wavelengths are seen as red light
• Knowing that light travels along a straight line in vacuum or any uniform medium leads us to the ray model of light.
• A ray of light is a straight line representing the path of a narrow beam of light.

• Speed of light is represented by letter $c$
• Speed of light is constant in the air and is 3.00×10⁸m/s
• Recall the equation $V=\lambda f$ to find the speed of waves, we can modify the equation in terms of speed of light $c=\lambda f$

• Luminous body emits light waves (sun, lamp)
• Illuminated body reflects waves produced by an outside source (moon, bridge)
• Luminous flux, is the rate at which light is emitted from a source
• Unit of luminous flux is the lumen
• The mount of illumination of a surface called illuminance,

$E =$ lumens per square meter $= lm/m^{2}$ OR lux, lx
$E = \frac{P}{4 \pi d^{2}}$
$P =$ luminous flux of the source
$d =$ distance between the surface and the source