Uncanny Atlas
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Full-spectrum and UV photography

Ghost hunters use cameras modified to record infrared and ultraviolet light as well as visible light, to look for spirits outside the range of human sight.

What users say it does
GhostStop, a seller of ghost-hunting equipment, says on its product page for the Phasm Cam that investigators use these cameras because spirits are thought to show themselves in those parts of the spectrum. That claim is the seller's; none of the other sources makes it.
What it measures
Wikipedia explains that a standard digital camera has a hot mirror filter which stops most infrared and a little ultraviolet, limiting the sensor to about 400 to 700 nm. Swapping that filter for one that passes a wider band lets the camera record the extra light more strongly.

Ultraviolet photography has an ordinary forensic history. Wikipedia notes that courts accepted it as evidence by 1934, and that it can show bruises or scars no longer visible on the skin and reveal altered documents.

Kenny Biddle, reviewing a set of claimed ghost photographs in Skeptical Inquirer, says cameras modified to record extra infrared and ultraviolet are usually mislabeled as full-spectrum cameras, and that the test he reviewed was far from controlled. McGill's Office for Science and Society reports Dany Plouffe's point that ghost hunters say eyeless spirits are put off by visible light yet tolerate infrared, and asks why a slightly longer wavelength would make that difference.

Sources