Fundamentals of Light & Optics

Particle (Photon) Theory

As proposed by Einstein, light is composed of photons, a very small packet of energy. The reason that photons are able to travel at light speeds is due to the fact that they have no mass and therefore, Einstein's infamous equation; E = mc2 cannot be used.

Another formula devised by German physicist, Max Planck, is used to describe the relation between photon energy and frequency - Planck's Constant (ℎ); 6.63x10-34 Joule-Second.

E = ℎv
or,
E = ℎv / λ


E is the photonic energy in Joules, is Planks constant and v is the frequency in Hz.


Light's particle nature, and ultimately the formation of light's wave-particle duality was confirmed by experiments conducted by Albert Einstein in the early 1900s, based on his study of the photoelectric effect and Planck's theories and results.

The photoelectric effect (PE) is where light striking a surface, causes electrons to be ejected from the surface, and will cause an electric current to flow across an applied voltage.

The photoelectric effect is the basis of operation of CCD image sensors, camera tubes, photomultipliers and image intensifiers.


In the next topic, we will study the properties of light and its behaviour.