[contravariant]

Like you said, the sun is 1 AU away, we're getting a fraction of its energy. Actually that fraction is still way beyond what were able to generate, and will remain that way for quite some time. However, we only need to illuminate the part of the earth with humans in it, which is a more manageable scale.

What we consider sunlight is essentially the light emitted by any object at 6000K, which is reasonably easy to achieve but somewhat difficult to contain. And actually mimicking the sun is usually not the best method (for one, the unfiltered UV would be very unhealthy). It's possible to approximate the visible part of that light though, and we're gradually getting better at it.