The all new reboot of Ghostbusters may have just breathed new life into an old franchise, and that success will probably crossover and generate renewed interest into the old art of ghost hunting. (I say art because it’s certainly not science.)

There are plenty of ways true believers try to justify the existence of ghosts with empirical data, and you can read here why they fall apart under real scrutiny. But one of those tangibles — optical evidence — deserves a little more unpacking.

The optics of ghosts can fall under two broad observations: what an individual sees with their two eyes, or a seemingly unexplained peculiarity picked up by photographic evidence.

The human eye is a feat of evolution, but it still has its limits. There’s a reason the phrase “eyes playing tricks” is so universally understood — our eyes sometimes see things that aren’t there, or cannot correctly observe the natural world and translate it into something logical. As you may know from personal experience, humans tend to sleep at night, so our eyes aren’t exactly stellar at seeing things in low-light environments. We don’t possess a membrane that nocturnal animals have called the tapetum licidim, which allows low light that hits the eye to bounce back to light receptors for brighter vision at night. For humans, light is absorbed once through our rods and cones — and it’s the former that are most active at night. Rods operate based on activity by the protein rhodopsin, which can take about 30 minutes to regenerate when you’re initially thrown into a dark setting.

Then there’s a condition called matrixing that occurs under low light. Matrixing is when the brain turns a poorly understood shape into something you already recognize. If you’re expecting to see a ghost, you’re going to interpret any bizarre streaks of light or odd shapes into the notion that it’s Casper or one of his asshole uncles.

That brings us to another way the naked eye (doesn’t) observe ghosts: when your eyes are fine but nature is cray. One of the most biggest forms of strange light phenomena that, for centuries, people have thought of as a sign that ghosts and supernatural spirits exist and wander the world is the ignis fatuus (Medieval Latin for “foolish fire,” and colloquially better known as the will-o’-wisp): a form of atmospheric light often seen by nighttime travelers who are close to bogs, swamps, or marches. These spectral, flickering lights were embedded in folklore as signs of ghosts.

The Will o' the Wisp and the Snake by Hermann Hendrich (1854-1931)

To compensate for the limits of the human eye, modern ghost hunters rely on photographic technology. These days, the lenses in cameras can arguably capture the world better than humans — so the idea goes that if a camera picks up something the human eye can’t, it’s gotta be real.

Surprise: It’s not. Cameras are technically superior to human eyes, but that doesn’t mean they aren’t subject to their share of flaws. There are a lot of different aberrations common to photography, but one in particular is called an orb, where a circular object on an image that is invisible to the naked eye, but very clearly visible in a photograph. These vaguely circular things appear to just be floating randomly. Some ghost hunters have claimed orbs to be concrete signs of a supernatural presence in a house or room.

Orbs around a burial mound. But they're not ghosts.

Visuals in this world are still a kind of work-in-progress. Our eyes are inundated in artificial forms of light as they have never been before — and human evolution has been slow to adapt to these things. Cameras are an extremely useful and important new technology, but they’re also still fraught with problems. And of course, there’s still a lot we don’t understand about the world, but that doesn’t mean strange lights are indicative of something that is otherworldly. Moral of the story: If it looks like a ghost, it’s probably not.

Pictured: legit ghost.
Photos via Hermann Hendrich, Kyle Tuinstra, Yonkers Ghost Investigators Official Website