I did this experiment with HPS 150W semiparallel (passive) ignitor gear

I power up the gear without a lamp connected to it, so hear the ignitor clicking as it attempts to strike

I hold the lamp (SON-T HPS or HPI-T metal halide) by the glass, away from the lamp base

I touch the center contact in the lamp base to the "La" wire from the ignitor, _to the isolation of the wire_

Result : lamp makes a faint (seen well in darkness) flash on every click of the ignitor

I also tried to touch it to the wire that connects to the socket (its the same node in the circuit, just another piece of wire with different type of isolation) and it does not make those flashes

The wire on the ignitor (which is part of the ignitor itself, not connected with terminals) looks like wire with standard PVC isolation, and made in 2006

The wire to the socket has some very thin shiny black isolation, and made in the 1970s



Why is the wire on the ignitor side "leaking" ?

High permitivity? Or cracked?
Or you touched it just by different part of the contact, where the metal was more rounded, so lower electric field...

The ignitor (which wires are "leaking") is new in excellent condition
It is the rightmost (newest) one here - http://www.lighting-gallery.net/gallery/displayimage.php?pos=-57645

The floodlight (which wires are not "leaking") is from the 1970s and quite worn out, but the original wires with thin black isolation are in excellent condition too
It is the right one here - http://www.lighting-gallery.net/gallery/displayimage.php?pos=-57709

I touched with the center contact of the lamp which is more or less round solder blob, without sharp points
HPS lamp is the one in the floodlight pic, MH lamp is this - http://www.lighting-gallery.net/gallery/displayimage.php?pos=-57595