# What gives light its energy to move

A photon, or particle of light, is released from an atom that has energy. Then the atom has less energy and the photon gets the energy the atom lost. Where did the atom get the energy? Heat is energy. In a hot substance the atoms have higher energy than in a cool substance. So a white hot wire in an incandescent light bulb is full of atoms with a lot of energy, and as it gives off photons it makes light and cools off. That is why you need to constantly add electrical energy to it with a wire from a generator to keep it glowing hot. The Sun is even hotter, and it's atoms get energy from nuclear reactions in it's core. Or a fire is hot and glowing from the energy of chemical reactions of the burning wood.

Since light has no mass, you can't calculate energy from speed they way you do with a rocket. For something with mass, it's kinetic energy, or energy of motion, is 1/2 times mass times speed squared. If mass is zero then energy is zero. Light has no mass so by that definition it also has no energy. But light can be thought of either as a particle or as a wave. Even better, it is BOTH a particle AND a wave. And it's energy is Planck's constant times the speed of light divided by wavelength. So shorter wavelength light, which is more blue, has higher energy than longer wavelength light, which is more red, even though both move at the same speed.

Source(s): http://pvcdrom.pveducation.org/SUNLIGHT/PENERGY.HT...