On Fri, 21 Sep 2018 12:59:12 -0700 (PDT), whit3rd
wrote:

On Thursday, September 20, 2018 at 5:32:27 PM UTC-7, Ned Simmons wrote:

The LED 8-footers available locally were drop-in replacements for the
fluorescent tubes, i.e., require the ballast to operate. Stupid. The
lamps I purchased connect directly across the line.

Maybe not so stupid. 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. That implies
about 175V across the 75W lamp once it's running. 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. I'll bet I've spent as
much time over the years replacing ballasts as lamps. I'd rather spend
the time up-front pulling them out.


--
Ned Simmons