Is light a form of energy, even though it is composed of photons, which have a (very small) mass?

Light has mass?

Light particles (Photons) are pure energy and exist only when in motion. We can debate if photons have mass. Because of Einstein's E = Mc^2 matter and energy are 2 forms of the same thing. Since photons have energy it can be argued that they have Relativistic Mass. On the other hand, Einstein was uncomfortable with the concept of Relativistic Mass because:

Many contemporary authors such as Taylor and Wheeler avoid using the concept of relativistic mass altogether:

"The concept of "relativistic mass" is subject to misunderstanding. That's why we don't use it. First, it applies the name mass - belonging to the magnitude of a 4-vector - to a very different concept, the time component of a 4-vector. Second, it makes increase of energy of an object with velocity or momentum appear to be connected with some change in internal structure of the object. In reality, the increase of energy with velocity originates not in the object but in the geometric properties of spacetime itself.

http://en.wikipedia.org/wiki/Mass_in_spe%E2%80%A6

http://en.wikipedia.org/wiki/Mass%E2%80%93energy_e...

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In any case, photons have zero Rest Mass.

No way does the definition say that "energy does not have mass". That might be the description of some property of energy, but it's not its definition.

Second, photons have no... none... nada... niente... neechevo... invariant (rest) mass. They are mass-less. In fact we can show that nothing can have the slightest bit of mass and still go the speed of light. My point is that you are wrong; it isn't there.

Bottom line, photons are pure energy, which we can find by E = hF, where h is a constant and F is the frequency of the photons.

Your premise that photons have mass is incorrect, or at least, its inconsistent with the photon theory. Whats odd about his theory is that photons are believed to behave like particles even though they have no mass. Photons are simply a quantity of light, which is pure energy.

Light is energy and photons have no mass.