Hello there Susan
I see your original expert has stepped away, perhaps I can help.
The condition you have is called Posterior Vitreous Detachment (PVD). Let me try to explain this in the best way I can. The back of the eyeball is full of a gel called vitreous. This gel is intimately attached to the retina and as we age, this gel liquifies, shrinks and pulls away from the retina. Where it was attached on the optic nerve, a small imprint is left, often described as a semi-circle or an out of focus cobweb. This is what I think you are seeing move back and forth in your vision. Your brain will learn to ignore it over time, and sometimes they settle a bit lower in your vision.. They will always be more noticeable against a blue sky or white wall.
If they increase in numbers or you get many new arcs of light in your peripheral vision, you need to be re-examined as soon as possible as it may indicate a tear in your retina. Over time the occasional flashes of light will become less and less frequent. I hope this helps explain the issue, if you have any questions, please let me know