Photon Energy (Wavelength)

This formula gives the energy carried by a single photon when you know its wavelength. It comes from combining two key ideas: light’s wave relation c = f\lambda and Planck’s relation E = hf, so substituting f = c/\lambda gives E = hc/\lambda. Because wavelength and frequency are inversely related, shorter-wavelength light has higher-energy photons.

Use this when converting a light wavelength into photon energy, such as in spectroscopy, photoelectric effect questions, or comparing UV, visible, and infrared radiation. It is also useful whenever a problem gives wavelength but asks for energy per photon.

• Using wavelength in nm without converting it to meters
• Calculating the energy of a beam without remembering this is energy per photon
• Mixing up the inverse relationship and thinking longer wavelength means higher energy