Lens flare is what happens when you aim your camera at a bright light source, like the sun. It is caused by tiny imperfections in the lens elements (the different pieces of glass that together form a single optical device). Lens flare is what we call the visible results of those imperfections. They usually look like light orbs, bows or circles, when created by using the sun as the light source.
However amazing the lens creating technology and process are, tiny little imperfections (lens defects) are nearly impossible to prevent entirely. So, it is still something you may encounter.
When light hits the lens elements, most of it will bend exactly like intended by the manufacturer, to get you the best possible photos. However, if a small percentage of all light that comes into the lens, fractures within it due to an imperfection in the glass, that will be visible in your photo, in the form of light disks, orbs or circles.
This is how you avoid lens flare
Avoid the phenomenon by making sure the super bright light that causes it, isn’t in frame. Either by reframing the shot, or using a lens hood. Try to zoom in and out a bit, it might cause the effect to go away. Another option is to change lenses. A prime lens (a lens with a fixed focal length) doesn’t create lens flare as much as a zoom lens. Also: keep your lens clean.
This is why you might not want to
Sometimes, lens flare is such a beautiful phenomenon, you can actually use it in your composition. Check out these examples:
As you can see, this lens phenomenon can be very pretty. So, maybe the best question shouldn’t be how to avoid lens flare, but how to use it to your advantage!