Why most "orbs" are dust, not spirits
That glowing circle in your flash photo is almost certainly a particle of dust or moisture caught by the camera's own light. Here's the physics behind orbs — and how to tell a real anomaly from a lens artefact.
Few pieces of alleged paranormal evidence circulate as widely as the orb photograph: a glowing circular blob floating in an otherwise ordinary image. Before drawing any conclusion, it is worth understanding exactly how these shapes form — because the optical mechanism is extremely well documented.
The physics of flash backscatter
When a camera flash fires, it sends a burst of light forward in the same direction the lens is pointing. Dust particles, pollen, water droplets, and small insects are constantly suspended in the air directly in front of any camera. If a particle is closer than the depth of field the lens can bring into focus, the reflected flash light bounces straight back into the lens. Because the particle is so close and so bright, the image records it as a large, luminous, out-of-focus disc rather than a sharp point.
This effect — backscatter — is especially pronounced with compact cameras and smartphones, where the flash sits physically very close to the lens. Camera manufacturer Fujifilm documented the mechanism in consumer support materials, and investigator Joe Nickell has stated that orbs in photographs result from these natural phenomena.
What about infrared cameras?
Orbs appear on infrared security footage for the same reason: bright near-infrared LEDs illuminate particles near the lens that are invisible to the naked eye, and the sensor renders them as circular blobs — sometimes dozens at once in a dusty environment.
How to tell backscatter from something genuinely unusual
A few practical checks: Was the flash on? Were conditions dusty or humid? Is there visible grain or a camera strap partly in frame? Does the orb appear in only one frame, or move in a physically coherent path? Backscatter orbs typically appear in isolation or in bursts in dusty conditions, at consistent apparent sizes. If something survives all of these checks, PRN's Evidence Guides walk through each step in detail.
Sources: Fujifilm consumer support documentation; Wikipedia — Backscatter (photography), citing Fujifilm and Joe Nickell (2010); PRN Evidence Guides — Photographs.