I have a fair bit of photographic experience and 99.9999% of all orbs I have seen in photos are dust and water particles or small bugs lit up by a camera's flash.
In one experiment, I (with a 3.2 megapixel happy snapper) and a fellow photographer friend of mine (with a 8 megapixel Canon DLSR with dust filter function) took photos at night and both using the flash. We took simultaneous photos of the same spots and my crappy camera had gotten tonnes of orbs where the higher quality camera did not. That camera was designed to remove dust and crap from the images. There are times an SLR or digital SLR may capture the same dust/water/bug particles however it is less frequent than the poorer counterparts.
How many people, without the flash, actually capture orb activity? Not many. Why? The flash is lighting up dust and water particles which airborne. It may also be noted that a lot of these occur at night where a flash may better light up said particles.
Even if an orb emits its own source of light, it may be a static or electro magnetic anomaly which do occur naturally under the right circumstances.
In summing, don't get excited about orbs until you have considered all the facts. If it emits its own light source, jump for joy, if it doesn't, throw it out.
Experience has shown, and a true philosophy will always show, that a vast, perhaps the larger portion of the truth arises from the seemingly irrelevant.