One streetlamp, one phone photo, and the frame is haunted: a procession of green and violet discs marches away from the lamp across the dark sky, none of which any bystander saw with the naked eye. The lens is clean, the sensor is fine, and nothing is wrong. Those discs are ghost images, secondary pictures created inside the lens itself when a bright source bounces between glass elements before finally reaching the sensor. Cameras regularly record reflections the eye ignores, which is the same privilege that lets a flash photo capture the red glow inside a person’s eye, or the green shine from a dog’s; lens ghosts are the version of that story where the reflection happens in the equipment instead of the subject.
A lens is a stack of faint mirrors
A modern camera lens is not one piece of glass but a stack of elements, sometimes a dozen or more, each with two polished surfaces. Every surface where glass meets air reflects a small fraction of the light that hits it; antireflection coatings shrink that fraction but cannot bring it to zero. When the scene is ordinary, those stray reflections scatter unnoticed. When a point source is hundreds of times brighter than everything around it, a lamp against a night sky, a sliver of its light can bounce off one element, strike another, and wander back to the sensor with enough strength to expose a visible spot. Optical engineers have modeled this arithmetic for decades, tracing ghost images surface by surface, and stray-light engineers still test for it because no consumer lens escapes it entirely.
Phones have made the ghosts harder to miss. Their lenses are small, their sensors hungry for light, and their night modes deliberately lift the shadows to recover detail, which also lifts any faint internal reflection into easy view. An interloper blob too weak to survive in an ordinary exposure can stride into a computational night frame at full strength, and each manufacturer then gets to decide how aggressively its software should recognize and erase such discs, a quiet negotiation between honesty and tidiness.
Photographers with room for accessories fight the same war with hardware. A lens hood, impossible on a phone, blocks the off-axis light before it ever enters the glass, which is why an outstretched hand, a cap brim, or a notebook held as a flag can do more for a phone night shot than any setting: the cheapest fix for stray light is geometry, and the second cheapest is a hat.
Why the blobs sit across from the lamp
Watch the ghosts instead of the lamp and they betray their geometry. Each internal bounce folds the path through the lens in a way that places the false image roughly on the opposite side of the frame’s center, at a mirrored position, and a chain of bounces produces a chain of blobs stepping away in size and faintness. Move the phone a little so the lamp swings across the frame and the ghosts glide with it, sometimes accelerating, sometimes shrinking, in a way no smudge of dirt ever would. On cameras with adjustable apertures the ghosts even change shape with the aperture setting, taking on polygon outlines from the iris blades, which is one of the cleanest proofs that the light passed the aperture more than once.
The flat cousin: veiling glare
Not all flare makes shapes. The same internal scatter that builds ghosts also delivers a diffuse haze across the whole frame, called veiling glare, which lifts black skies to gray and quietly steals contrast from night scenes. Standards and testing programs treat it as a measurable property of a complete optical system, graded under controlled light sources, because the amount of veiling tells you how much of a bright scene a lens can survive before its shadows stop being black. It is the same physics as the colorful ghosts, just spread thin instead of focused into blobs. When your night photo also fills its shadows with red, green, and blue confetti, that is a different mechanism entirely: the statistics of scarce light documented in the color speckles of night photos.
Living with the ghosts
Photographers manage ghosts rather than defeat them. Small changes of framing swing the blob train onto or off your subject; a hand brimmed over the lens, playing the roof of a hat, blocks the offending source from striking the front element at all; and phone makers increasingly run computational cleanup that recognizes and damps the disc pattern, with imperfect and sometimes overenthusiastic results. None of this is a defect to be repaired. It is the honest price of putting many surfaces between a very bright point and a very dark frame.
The colors themselves carry a small extra lesson. Ghosts often arrive tinted green or violet because coatings suppress reflection unequally across the spectrum, so the leftover bounce is not neutral; you will frequently catch a green and a magenta blob traveling together, two hues facing each other across the wheel, a pairing you can explore directly in Complementary Color. Next time a lamp acquires a spectral escort in your photo, you can read the whole exchange: one bright source, many faint mirrors, and a frame that politely drew the reflection map for you.