Direct or scattered light hits the lens, creating halos, ghosts, or washed-out zones — a flaw in bad backlighting, style choice in Kubrick and Abrams.
When light hits your lens directly or indirectly, while the sun or a strong source is in or near the frame, something fundamental happens: the glass elements of the optics become a scattering surface. The result is halos, ghost images, or a milky, washed-out area in the image — lens flare. Not to be confused with natural overexposure: this is pure optical physics, and it hits you faster than you think.
In practice, this is the nightmare during backlight setups or when the sun is just outside the frame. Every air element between the source and the sensor becomes a reflective surface, especially with older or coated lenses with many elements. You'll recognize it immediately: characteristic circular reflections that run diagonally across the image, or a diffuse flicker in the highlights. Some lenses are more affected than others — an old Super-16 lens can be terrible, while a high-quality modern Zeiss lens is robust. This is due to the coating and the optical design.
Remedies are well-established: a lens hood (the first thing you should check), additional lens filters, or you simply position a flag between the light and the camera — often the most elegant solution. Some also use diffusion in front of the source. But beware: a polarizing filter often reduces flare significantly, but costs you one stop of exposure.
The second story is its deliberate application. Kubrick and Abrams have shown that lens flare works as a visual stylistic device — it suggests brightness, energy, technical aesthetics. The Abrams-typical anamorphic flares have become almost his signature. This is not a mistake, it's design. If your director wants it, you need the right backlight constellation and often a follow-focus artist who refines the flares during the shoot.
In summary: know your lens, its susceptibility, and the position of the sources. Lens flare is either the annoyance you eradicate or the tool you use precisely. Both require craftsmanship.