In CA, it's now the law - if the American flag is left out 24/7, it must have a light, so it is visible at night. Any type of light is OK, nothing has been specified.
We couldn't aford to instal alight on/near our flag pole and our schedule did not permit us to put it up at sunrise and down at sunset, so I lowederd the pole and inserted a solar light at the top of the pole. No, she's lit at night and it's all natural.