Brightness of streamers vs. ground strikes

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Steve Conner <steve@xxxxxxxxxxxx>

Hi all

I was puzzling over something recently. When messing around with my DRSSTC-

http://www.scopeboy.com/tesla/drsstc/woot.jpg
http://www.scopeboy.com/tesla/drsstc/zoot.jpg

The ground strikes do not seem any brighter than air streamers. Now on 
pictures of larger coils, ground strikes always seem brighter and a 
different colour. I remember one picture by Peter Terren where the air 
streamers are dim purple and the ground arcs are a lightning-like blue-white.

I wonder if this has to do with the frequency of the coil? As the frequency 
goes up, the current drawn by air streamers will increase and they will get 
brighter. Ground arcs won't change since they are purely resistive.

If we thought about this- and it seems to happen about 200-250kHz for 3ft 
streamers since my 260kHz spark gap coil behaves about the same- maybe it 
would tell us something about the nature of streamer loading?

To me it says that a 3ft streamer has a resistance about equal to or 
greater than its capacitive reactance at 200kHz. Also that the resistance 
of a 3 foot ground arc is much the same as that of an air streamer the same 
length. But I don't know if I'm reading too much into it.

Also it should be qualified by length- I imagine if I let the coil arc to 
ground over a shorter distance it would be brighter.

Steve Conner