Re: Three lighting questions -- or maybe it's 4 or 5 now

["S. Hieber" <shieber at yahoo_com>]

> Those plant and aquarium lamps are notoriously shortlived. You can
> buy
> lots of 40 watt t12s with 20,000 hour lifespans. 40 watt T12s are not
> designed for instant start though and that could be part of the
> problem
> as well.

Rapid Start Ballasts and lamp life:
Some "rapid start" ballasts maintain a filament current after the bulb
is lit.  Rapid start bulb filaments are designed to handle that and the
extra heat helps the bulb light up.  Couldn't some of the increased
wattage form overdriving, when using a rapid start ballast, be going
into raising the heat of the filaments?  That might help brighten the
bulb (increased ionization) even further but it's very hard on the
filaments.  So, for overdriving, a soft start ballast would seem to be
preferable, other things being equal.  Or, at 8-12 hour cycles, an
instant start *might* even be preferable, in terms of bulb life.  

Too bad the bulb/ballast makers don't publish all this info.  :-(

Overdriving, Bulb Temps, and brightness:
Fluorescents are rather sensitive to temperature values.  Try this: put
a fan in one end of an aquarium hood containing a PC55.  See if the end
without the socket, the "colder" half of the bulb, has a visibly
different brightness level than the "hotter" half.  The *color* of the
bulb might be a bit different on the colder side too.  It will depend
on how hard your ballast drives your bulb, how much air your fan moves,
etc.  

Fluorescents do well when the glass temp is roughly 125 degrees F. (It
depends on what the bulb maker designed for but that's a common value,
give or take).  That's very hot to the touch, but not scarring.  Below
that kind of temp, the light output lessens.  

Focusing the fan on the "cold" end and exhausting the hood air at the
"hotter" end is the most efficient set up for cooling.  But it's not
the most efficient set up for lighting!  

Some of the increased brightness from overdriving might be coming from
increased bulb temp.  But that works only up to a point and hotter is
harder on bulb life than cooler.  So the question comes up again,
what's a good match for overdriving a particular (type of) bulb?

But who's counting:
Of course, fluorescent bulbs and ballasts are so flexible, that lots of
combinations work that aren't the design optimum.  And some of this
stuff is so cheap, that optimum doesn't really matter that much.  But
this territory hasn't been very well mapped -- at least, not for the
laity.

Scott H.

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