Photon energy is the energy carried by a single photon with a certain wavelength and frequency. These terms are related by an equation. E = hv where h is the Planck's constant (6.626 x 10-34 J s), v is the frequency which is related to the wavelength by:
λv = c where λ is the wavelength and c is the speed of light (3.00 x 108 m/s)
Therefore, the energy equation E = hc / λ E = (6.626 x 10-34 J s)(3.00 x 10^8 m/s) / 0.127 m = 1.565 x 10^-24 J