On Friday, September 21, 2018 at 5:36:05 PM UTC-7, Ned Simmons wrote:
On Fri, 21 Sep 2018 12:59:12 -0700 (PDT), whit3rd
wrote:

... The 'require ballast' lamps get about 24V of
excitation, which means seven or eight LED diodes in a series string, with
other strings in parallel. The 'full voltage' get 240V, so that's
seventy or eighty in series.

Where do you get 24V? A standard ballast for 8 foot F96T12 lamps
outputs 750V for starting the lamp and 425mA operating.

The LEDs are more efficient, but the ballast still chokes current at circa 425 mA.
So, the voltage is lower for LEDs than for tubes. My '24V' number is only order-of-magnitude.


...Now, in addition to
the internal LED driver(s) in the lamp, you have a point of failure,
the ballast, that's not doing anything useful.

But, it IS buffering the LEDs from voltage spikes, without the power-wasting resistors
used in some lamp-replace series strings. The starter-boost is a complex part
of the ballast, but isn't required for the LEDs; if it fails, you'll never notice.
The 'internal LED drivers' in the one lamp I dissected, were... only rectifiers to prevent
reverse voltage.