You're scrolling back through photos from last Saturday and there it is: every lamp post wearing a soft, milky crown, the neon bar sign bleeding into the dark like a wet felt-tip dragged sideways across paper. You were standing right there. You saw none of it. So what, exactly, is your phone looking at?
Your eye and a phone sensor are solving the same problem (capturing a scene where brightness levels vary wildly from one corner to the next), but they solve it in completely different ways. The halos are a side effect of the phone's solution. A pretty bad one, honestly.
The sensor's impossible task
A modern phone sensor is a grid of millions of tiny photodetectors, each collecting photons and converting them to an electrical signal. The problem is dynamic range. A lit streetlamp at night might be emitting thousands of times more light than the pavement a metre below it. The sensor has to record both in a single frame.
When a tiny photodetector gets hit by far more light than it can hold, it overflows. The charge bleeds into neighbouring pixels. Engineers call this blooming. The result on your image is a glow radiating outward from any bright point source, because the pixels physically adjacent to the overloaded ones are reading contaminated values.
That's the halo. Not a lens artifact. Not a software glitch. Electrons literally spilling over a wall.
The lens makes it worse. Cheap, thin optics scatter a small fraction of incoming light across the whole frame rather than snapping it to a clean point. This is called veiling glare, and it's the same reason a vintage lens gives portraits that dreamy, washed look. On a phone, the effect concentrates around anything bright enough to generate significant scatter. A warm streetlamp at 2,700 kelvin is basically a perfect target.
Your eye handles all of this without producing halos, and the reason is almost embarrassingly elegant. Your pupil is a dynamic aperture that physically constricts in milliseconds when pointed at a bright source, throttling the light before it ever hits the retina. Your retina uses two separate receptor populations, rods for low light and cones for bright, and your visual cortex stitches their outputs together into one coherent image. You are running a biological HDR pipeline in real time.
The phone is not.
What the software tries to do about it
Modern phones run computational photography algorithms that attempt to compress dynamic range in post. The camera shoots multiple exposures in rapid succession, sometimes three, sometimes seven, aligns them, and blends them. Google's Night Sight and Apple's Smart HDR both work roughly this way. Blending exposures, though, doesn't eliminate blooming that already happened on the sensor. It can reduce halos, and on flagship hardware it does meaningfully reduce them. It cannot erase physics.
There's also a lens coating story here. Premium phone makers apply multi-layer anti-reflective coatings to reduce veiling glare, which is why a photo taken on a mid-range phone and the same shot on a current flagship genuinely look different around light sources. Not because one phone is smarter. Because one has better glass with better coatings that scatter less light to begin with.
Here's a concrete illustration. Take two people who bought different phones in the same product cycle: one a mid-range model with a single-layer coated lens, one a flagship with seven-element optics and nano-coating. Same street, same lamppost, same night. The mid-range shot shows a halo easily 40 pixels wide around the lamp. The flagship cuts that to roughly 12 pixels. Both still have halos. Your eye had none.
Have you ever wondered why the "fix" never shows up in the camera settings menu? Because there isn't one. The fastest practical fix is framing: move the bright source to the very edge of the shot, or just out of it entirely. Blooming and veiling glare both fall off steeply with distance from the offending light. You lose the lamp, but you keep the scene.
The deeper irony is that the halo has become aesthetically load-bearing. Bokeh, lens flare, light bloom: photographers spent decades learning to love the artifacts of imperfect optics, and phone cameras are simply producing their own generation of imperfection. It annoys people right now precisely because it's new and not yet wrapped in nostalgia. Give it twenty years. Someone will be selling a filter that adds it back in, and calling it cinematic.