How much energy do individual photons of 450 nm light have?

4.4 x 10^-19 joule Planck's equation will give you the energy of a photon given it's frequency. But since we have the wavelength, we first need to find the frequency by dividing the speed of light by the wave length. 299792458 m/s / 450 x 10^-9 m = 6.66205 x 10^14 1/s Now multiply by Planck's constant 6.66205 x 10^14 1/s * 6.62607004 x 10^-34 m^2kg/s = 4.41432 x 10^-19 m^2kg/s^2 = 4.41432 x 10^-19 joule Since we only have 2 significant digits, round the result to 2 significant digits. = 4.4 x 10^-19 joule