1 mole of light contains 6.02 x 10²³ photons
Energy of a given wavelength of light is given by:
E = nhc/λ; where n is the number of photons, h is the Planck's constant, c is the speed of light and λ is the wavelength.
E = (6.02 x 10²³ x 6.63 x 10⁻³⁴ x 3 x 10⁸) / (400 x 10⁻⁹)
E = 299.3 kJ
