Ian Stirling wrote in message ...
N. Thornton wrote:
(Andrew Gabriel) wrote in message ...

Good account there. I'd just add 2 things: electronic ballasts dont
always ensure perfectly symmetrical current flow in the 2 half cycles,
hence the line frequency element of flicker can still occur with some
types.

All the electronic balasts I've taken apart (probably 5-8 different models)
have a bridge rectifier/capacitor before everything else.
The only asymmetry could arise from differential heating of the diodes,
or manufacturing differences.
This is going to be at the very outside 30-50mv.
On a line going to +-340V, this is effectively zero.

A bridge rec isnt going to prevent asymmety though. A series cap will,
a reservoir cap wont. The first electronic fitting I had flickered
severely during start up, at 50Hz.

Regards, NT