Are you talking about a discharge in full pressure (1 atm) air? AC or DC? If your power supply is only capable of a small current, then it is likely that your arc is really stopping and starting many times per second (power supply output capacitance charges until arc breaks over, discharges until the current is too low to support the arc, arc stops, process repeats). The voltage drop of the arc will vary considerably during this process and it could be that the highest power dissipation is happening toward one spot in the arc during the beginning when the voltage is highest. Also, there will be a direction of flow in the ionic current and a difference between where the ions are being created and where they are re-combining. If the arc is DC (as in, never changes polarity), then one electrode will be the main ion creator and the other the main ion re-combiner. What are the shapes of the electrodes? It is also somewhat random exactly where the arc begins. The most generally accepted theory is that there is some initial ionization of the air due to background radiation and the air breakdown begins from this point, forming an avalanche discharge until the arc is established. This will probably begin in an area where the E field is strongest, but if the electrode has certain symmetry then there may be a whole ring (or other shape) of places with equal E field strength near the electrode and the arc will start near any random place along this ring. This can in turn influence the path that the completed arc takes. This could cause a variation in intensity within the arc that you could see. Sean On Thu, Apr 2, 2015 at 8:57 PM, David VanHorn wrote: > It looks really interesting, but I've never been able to photograph it. > Not wanting to get any electronic camera too close. > > The air in this case is in a closed tube, so there's no external > disturbance, but I imagine a pretty good ion wind. > > > On Thu, Apr 2, 2015 at 6:09 PM, Jason White < > whitewaterssoftwareinfo@gmail.com> wrote: > > > The following is speculation: > > > > * Perhaps those are higher resistance (drier) zones in the air. > > Increased resistance could lead to increased heating, > > > > * Conversely, air that has been heated by the arc into plasma is > > highly conductive, perhaps the low resistance of the plasma "funnels" > > the arc into hot zones causing localized heating (bright spots). > > Perhaps the arc is more spread out outside of these bright spots > > resulting in less localized heating (and a less visible arc). > > > > > > > > On Thu, Apr 2, 2015 at 7:52 PM, David VanHorn > wrote: > > > Something that I've been wondering about, as I look at high voltage > > sparks. > > > > > > Within a single spark, along its length, there are sometimes zones th= at > > are > > > much brighter than the rest of the spark. A given spark might have > three > > > or four of these, or none. > > > > > > Any ideas what causes this? Could it be my eye rather than the spark= ? > > > -- > > > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > > > View/change your membership options at > > > http://mailman.mit.edu/mailman/listinfo/piclist > > > > > > > > -- > > Jason White > > -- > > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > > View/change your membership options at > > http://mailman.mit.edu/mailman/listinfo/piclist > > > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .