Aside from the film grain, I'm pretty impressed that the camera seemed to survive that and that the footage from it could be extracted like nothing of this nature had ever happened to the device.
because only product being irradiated goes there. no human should be in that area. plus with the lights off you see the ionized air. that would probably be washed out with another light source.
the lighting should be consistent throughout the experiment so that the effect of the radiation cannot be confused with change in light levels. goodness, why would someone need that explained to them? you must not be the inquisitive type.