Now let's get this straight.
ORBS ARE NOT SPIRITS
One of the most common assertions by so-called professional paranormal investigators is that 'orbs' on a photograph (usually digital) are 'spirits'.
Such statements do nothing for their own credibility, but more importantly transform the whole field of paranormal research into a smelly bog.
There are a number of reasons that 'orbs' can be captured - I shall list some. The observant reader will notice the significant absence of 'spirits' or 'faeries'.
1. Dust (even pollen!) - one of the biggest causes of orbs. This is especially the case then a flash is fired. Dust particles in the air reflect the light and appear - yes, you guessed it - as orbs. Of course you didn't see the dust particles when you took the picture. Would you have expected to?
2. Moisture - another major cause of orbs. Not unlike dust, moisture in the air can actually reflect light - gasp, horror! And not unlike dust, these particles are not two inches big and carrying large signs reading 'i am moisture'. You don't normally see them when you are taking the picture. But the cameras, bless them, do!
3. Insects. Yep - sometimes really tiny ones. They can appear very orb-like or even as hideous demonic forms. Especially when they are close to the camera and out of focus or flying by.
Now some might suggest that digital cameras could be more sensitive to infrared light and that ORBS could appear due to some ghostly manifestation as pinpoints of infrared.
The fact is that digital cameras are very much more sensitive to infrared light. So much so, that to take decent photographs, it was necessary to include infrared blocking filters on most digital cameras. Which means very little - if any - infrared light gets through. As I shoot considerable footage with specially modified infrared cameras, I can assure you that most off-the-shelf point-and-shoot cameras have more chance of photographing an honest politician than anything in infrared.
The biggest 'push' with respect to ORBS is that they are some sort of energy source. But if you blow up orb pictures, you do not get a characteristic energy image - a bright point decreasing in brightness. Instead, you get something with varying pixelization in a manner that suggests that it is a (tiny) three-dimensional object reflecting light. Not a light source.
There are many images that remain speculative, where the captured 'manifestation' cannot be easily explained. Digital cameras MAY be more sensitive to light in ways we are unaware. Perhaps they pick up other radiations which, unlike infrared, are not filtered out. The jury is well out on whether or not ghostly images can be explained away by the cynical skeptic - all out to believe in nothing regardless of any evidence. Ghosts - or some other paranormal activity - may well be captured on camera.
But ORBS are not paranormal activity. Just an indication of site contamination by dust, moisture or other particles.