On 9/13/2011 10:55 AM, Antonio Vernucci wrote:
Nope.. you can't usually see the corona discharge. The professionals
use a special camera with a narrow band solar blind filter.

That is interesting.

But I presume that, increasing voltage, at a certain point the corona
effect becomes visible.

Yes.. but that's usually a LONG way from where there's detectable RFI or
noise for instance. When you can see visible corona from some meters
away, you're probably in the 10s or maybe low 100s of kV range.

For instance, I can run my small 14" Van deGraaff generator with no
visible corona in a semi-darkened room, but, judging from the copious
ozone production, there's quite a bit of corona (as well as the
characteristic crackle sound).

Maybe people have seen noticeable corona at 2-3kV, but that's usually
indoors in a dark room, and you're fairly close and well dark adapted.
Corona from aged ignition wires (around 15-20 kV) also often visible, in
the dark.