The best proof that light is energy is... Earth.
Except from volcanism and earthquakes that come from the inside, and tides due to its rotation around its own axis,that is not synchronized with the moon, all the energy on Earth got here... by way of light from the sun.
Weather is driven by differences in temperature of regions that get more or less light from the sun, of the amount of water vapor that is evaporated from the seas by the heat generated by light from the sun.
Except for deep-ocean volcanism that allows for pockets of life, almost all life on Earth is supported by photosynthesis that uses light from the sun.
Coal and oil come from plants buried long ago but that also grew thanks to photosynthesis.
Energy that arrived in form of light from the sun is everywhere.
Here I will answer more precisely to a comment by the author of the question, namely Predaking Askboss, just under his original question.
If it doesn't have mass then it can't have kinetic energy. So how does
it store energy in it? Can we say that there is no energy in its
It is a very frequent fallacy to believe that light, or a photon, has no mass.
Of course it has mass. What is zero is its rest mass. Since light, that is photons, can never be at rest, one cannot measure directly rest mass. But we know it is zero as I'll explain below.
Particles (or objects) that have a nonzero rest mass can be at rest and have their rest mass ($m_0$) measured. When in motion, their total mass in motion $m$ is higher than their rest mass by their kinetic energy divide by $c^2$
For a photon, what is zero is the rest mass $m_0$. The total mass in motion of a photon is just
where $E_k=\hbar \omega$ is all its energy. And this is how we know it has zero rest mass.
And light, or photon also has momentum. The momentum $p$ of a photon is its total mass in motion multiplied by its velocity, which is $c$
So you can actually use the momentum of light to push a lightsail in space, for instance. This is direct use of the radiation pressure of light, which is the incoming flux of energy by unit surface divided by $c$. This however, is a very inefficient way to use this energy.
Consider a car at rest on a very flat road. If you have a squirt gun, you can use 10 gallons of gasoline to move the car : fill your squirt gun with gasoline and aim the jet at the car. Over and over and over till the 10 gallons are used. You will probably manage to displace the car by a few centimeters. Use the same amount of gasoline in the engine, you drive many kilometers.
Using the momentum of light on a lightsail may be practical in deep space, not very much on Earth. What you really want to do is turn the energy $\hbar \omega$ of light into heat, or even better, into chemical energy and use it later.
Incidentally the solar light mill, or Crookes radiometer presented by foolishmuse does not really use the momentum of light. If it were the case, it should turn black face forwards, because the dark face absorbs the photons an receive their momentum, but the silver face reflects them and thus receive twice their incoming momentum, since when they are reflected they carry away the same momentum in the opposite direction. That would indeed be the case in perfect vacuum.
But even though there is a partial vacuum in the glass sphere there is much too much air left to work this way. In fact you can see on the wiki page that it turns silver face in front.
The silver face reflects the light and stays cool. The black face absorbs then and heats up. This heats up the small amount of air in the immediate neighbourhood of the black face. This air expands by heating and pushes the black face away. Hence the rotation silver face in front.
So even this solar light mill is an application of the heat transported as energy by the light, not its momentum.
But energy, momentum and total mass at rest are all nonzero for photons.