To answer your question and comment on the photo. Orbs can be and are almost any size. These particular orbs are particle orbs that are illuminated by flash photography.
We touch on this subject quite often. When a standard camera is used with a flash, the flash is at such an angle that any particulates in the are are illuminated so brightly that they form an out of focus brilliant light source. This light source in turn becomes what we see as an orb.
These orbs an show up as many different sizes, and there can be many different orbs. They are caused by physical phenomena.
Flash photography *CAN* be safely used in a way that it does not create orbs. But generally you must use an upper end camera which allows you to attach an external flash which is at an angle not directly in line with the camera.
Now please don't get me wrong, I firmly believe there are real non-flash related orbs out there. And they can also be of many different sizes and types. But unless special flash equipment is used, you will likely never find them in a photograph taken with a flash.
