From: Martin McCormick <martin.m@suddenlink.net>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
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Date: Wed, 25 Nov 2020 15:01:30 -0800
Subject: Re: [OT] Hyperikon Retrofit LED Tubes Without Ballast
Thread-Topic: [OT] Hyperikon Retrofit LED Tubes Without Ballast
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"Harold Hallikainen" <harold@mai.hallikainen.org> writes:
> This discussion reminds me of just how interesting fluorescent lamps are.
> Wikipedia has a nice article at
> https://en.wikipedia.org/wiki/Fluorescent_lamp .
>=20
> Many years ago, I did some work on fluorescent lamps for television
> lighting. I always thought the ballast was interesting. An oscillator wit=
h
> an H-bridge drove the lamp. The H-bridge drove the lamp through an
> inductor. The H-bridge with series inductor was connected to one filament
> pin at each end of the lamp. A capacitor connected the other filament pin
> at each end of the lamp. Before the lamp fired, the LC was resonant
> causing a high current through the filaments, lighting them. The resonanc=
e
> also created a high voltage across the capacitor and across the tube. The
> filament heating and high voltage across the tube would ionize the gas,
> shorting out the capacitor. The inductor then became a current limiter.

	Wow! that is clever.  Were the fluorescent lights being
driven at an RF frequency to avoid heterodyning with the
not-quite 30-HZ frame or not-quite 60-HZ field rate?

	I understand that monochromatic or black-and-white video
of the late 1940's and early fifties was meant to be exactly 60
HZ for fields and 30 HZ for the whole frame but color TV was
required by the FCC to take absolutely no more spectrum than
black-and-white so one way to make it all fit was to
ever-so-slightly slow down the frame rate so that 525 lines plus
the color burst at the beginning of each line didn't splatter in
to the audio carrier of the channel below the video carrier or
the guard band between the top of Channel X and the start of
Channel X+1.

	Conventional Fluorescent lighting has a lot of flicker at
120 HZ which human vision can't see but I bet it louses up video
pickups, both the old videcon tubes and probably CCD pickups used
today in solid-state cameras.

	People who are blind use so-called light probes to "see"
if lights are on or off such as anything from room lights to
indicator lights on panels.  These are RC oscillators with the R
being a photo cell such as a solid-state device or one of those
cadmium dysulphyde photo cells which are also called light
dependent resistors.  Light makes the resistance drop from almost
infinity in a dark room to around 1 K-ohm or less.  Light in the
mid spectrum range causes the oscillator to rise to several
kilohertz if seriesed with a .1 UF capacitor.

	If you hold one of these under an incandescent lamp, you
hear a little power-line frequency modulation of the whistle.
Under a fluorescent lamp, it's a regular growl at 120 HZ or 100
HZ in 50-HZ land.  You can even hear some 60-HZ modulation if you
move the photo cell near the ends of the fluorescent tube where
the cathodes are since each cathode alternates between being a
cathode and an anode every half cycle.

	Yes, Fluorescent lamps are fascinating and gas discharge
tubes such as the little NE2 and NE51 lamps of yesteryear are
really interesting gadgets since they do not conduct any
electricity until one reaches the breakdown voltage of the gas
and begins knocking those electrons out of their orbits which
make Ions and current flow. =20

	Well, I guess I have gon off topic of my off-topic post
so I better sign off now.

Martin McCormick WB5AGZ
--=20
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