The "classical" view of light is as a wave. The wave involves perturbations in both the electric and magnetic fields as light travels through space at the speed of light (299800 km/s). For simplicity, only the electric field perturbation is shown in the two examples below. Both show ultraviolet light with wavelength λ = 450 nm (and frequency = ν = c/λ = 0.67 x 1015 s-1). The difference between the two examples is that the intensity of light is greater by a factor of two in the example on the right (this corresponds to an increase in the amplitude by a factor of the square root of 2). According to classical theory, the energy (intensity x time) of the light can be made as low as wanted by reducing the amplitude, no matter what the wavelength.
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The quantum view of light is as a particle-like wave packet, represented below. Each wave packet is called a photon. Each photon of a certain wavelength has the same amplitude and shape, so that the energy of each photon is the same. The energy of a photon is given by Planck's equation: E = hν = hc/λ. Higher intensity of light corresponds to a greater number of photons passing by per unit time.
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All of the examples above involve light with wavelength 450 nm (blue light). The time in femtoseconds is given at the top of each screen; with careful observation you can confirm that any given wave peak travels 3.0 μm in 10. fs, which is equal to the speed of light:
3.0 μm / 10. fs
= 300 nm/fs
= 300 μm / ps
= 300 mm / ns
= 300 m / μs
= 300 km / ms
= 300,000 km / s.