Re: Dimming Fluorescent Ballast as Video Pixel

On 25 Apr 2006 23:33:43 -0700, "Damon"
<damonseeley@xxxxxxxxx> wrote:

I am interested in arranging fluorescent lights in a large matrix such
that each lamp is like a pixel in a monochrome video display. To
accomplish this means that the "pixels" would have to respond to
dimming control very quickly and dim to a low level. These are the
questions I am seeking to solve before continuing:

I believe there are large display panels that already use
fluorescent lamps as pixels, but the only reference I can
find is for the Jumbotron, which uses a vacuum fluorescent
display not a mercury-rare gas discharge. But, the
Jumbotron probably also uses a special rapid decay phosphor
- see below.

- Will a commercially available dimmer's response time be fast
enough? Some of the kinoflo studio fluorescents I have seen exhibit a
2-3 second delay when controlled via DMX.

As others have asked, how fast do you need the system to
change intensity? As you have guessed, your first challenge
will be the speed of the dimming ballast, but as you
approach normal video display speed you will find that the
phosphors used on conventional lamps may not be fast enough.
- Will constantly dimming a fluorescent tube shorten its
life, or is it
only cold starting that hurts lifespan?

Dimming will reduce lamp life if the ballast is not properly
designed. Rapid changes in intensity may reduce lamp life
even with a properly designed ballast since the electrode
temperature cannot change as fast as you may need the
discharge current to change. In that case, a system that
operates the electrodes at rated voltage all the time will
provide the best performance vs. one that reduces the
electrode voltage when the discharge is operating at rated
current.

- Does anyone have experience with Osram, Advance or Lutron dimming
electronic ballasts in a similar application? Each company makes a
"1%" dimmer that I could theoretically control with 0-10V input.

No, but you should be able to get the info you need on
dimming speed from the manufacturers.

- Are there advantages to dimming T5 HO vs. T5 vs. T8 lamps in terms of
dimming smoothness, lifespan, etc?

Your needs go far beyond what is normally called dimming.
Unless you get a response from someone with specific
experience with fluorescent lamp-based display systems you
may have to run your own experiments.

--
Vic Roberts
http://www.RobertsResearchInc.com
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