# So I was thinking about Light, right ?

## Main Question or Discussion Point

...and I was wondering,

Light travels at 670,616,629mph, which is rather fast.

For light to travel that fast, it must carry a huge amount of energy, surely? So, if that's the case, why do we get so comparatively little from current solar energy mediums?

Are there any ideas or theories that might help get more out of it?

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berkeman
Mentor
...and I was wondering,

Light travels at 670,616,629mph, which is rather fast.

For light to travel that fast, it must carry a huge amount of energy, surely? So, if that's the case, why do we get so comparatively little from current solar energy mediums?

Are there any ideas or theories that might help get more out of it?
Light travels the same velocity whether it is dim (single photon) or intense. Don't confuse the speed of light with the energy carried by that light. The energy carried ratios with the number of photons and the inverse of their wavelength, and has nothing to do with the speed of the photons.

How does that work? I suppose I'm thinking of it in terms of a bullet, an object going that fast would be pretty hazardous. And I suppose a bigger bullet at the same speed would obviously carry more energy.

So is it the case that photons are just stupidly small, and the more you have the bigger the bullet? Or am I thinking of this wrong?

Photons are massless. I think you're thinking in terms of, something massive that was going that fast would have a great deal of inertia. (Though something that's massive cannot reach the speed of light.)

berkeman
Mentor
How does that work? I suppose I'm thinking of it in terms of a bullet, an object going that fast would be pretty hazardous. And I suppose a bigger bullet at the same speed would obviously carry more energy.

So is it the case that photons are just stupidly small, and the more you have the bigger the bullet? Or am I thinking of this wrong?
For photons, each individual photon carries an energy of $$E = h \nu$$ where h is Planc's constant, and $$\nu$$ is the frequency of the photon in Hz.

http://en.wikipedia.org/wiki/Photon

The total energy in an electromagnetic wave is the sum of the energy in the individual photons making up that wave (or composite waves).

But, given the speed they're going, wouldn't there be a lot of kinetic energy?

Doc Al
Mentor
But, given the speed they're going, wouldn't there be a lot of kinetic energy?
As berkeman stated, the energy of a photon is E = hf. Speed is not a factor.

russ_watters
Mentor
But, given the speed they're going, wouldn't there be a lot of kinetic energy?
Since they have no mass, the kinetic energy equation is irrelevant.

jtbell
Mentor
I suppose I'm thinking of it in terms of a bullet,
Don't think of photons as like bullets. They're quintessentially quantum objects, and you quickly run into trouble when you try to visualize them in classical terms.