Hi folks,

This is tangential to my post about an internally lighted sign, in which
Dean and Douglas are helping. It appears that we're going to be able to
use only about two 48" fluorescent tubes to not go over the city
ordinance for maximum light. This is all very rough numbers at at this
stage. But this sign will be about 4' x 8', and about 9" deep, making it
hard to spread the light out uniformly from only two such lamps.

I divide the world into two types, politicians and scientists. The
politician in me says "don't worry about it, just use multiple tubes to
get the even light, and put filters in to eat up the extra light." But I
don't like that side of me. The scientist in me says to try
to do it efficiently.

So I wonder if we can use more tubes, and run them at lower current. It
would seem that some extra inductance in the ballast would give us less
current. I think I've read in Don Klipstein's pages that fluorescents
can fail prematurely in such conditions, but I can't find the reference.
Any thoughts on running fluorescent tubes at lower current? Bad idea? If
not, how to go about it.

Hi folks,

This is tangential to my post about an internally lighted sign, in which
Dean and Douglas are helping. It appears that we're going to be able to
use only about two 48" fluorescent tubes to not go over the city ordinance
for maximum light. This is all very rough numbers at at this stage. But
this sign will be about 4' x 8', and about 9" deep, making it hard to
spread the light out uniformly from only two such lamps.

I divide the world into two types, politicians and scientists. The
politician in me says "don't worry about it, just use multiple tubes to
get the even light, and put filters in to eat up the extra light." But I
don't like that side of me. The scientist in me says to try to do it
efficiently.

So I wonder if we can use more tubes, and run them at lower current. It
would seem that some extra inductance in the ballast would give us less
current. I think I've read in Don Klipstein's pages that fluorescents can
fail prematurely in such conditions, but I can't find the reference. Any
thoughts on running fluorescent tubes at lower current? Bad idea? If not,
how to go about it.
--
Earl
It's certainly possible to run the fluorescent lamps at lower current; but,

"Earl Kiosterud" <someone at (no spam) nowhere.com> wrote in message news:qG5Vj.619$T1.136 at (no spam) trnddc01...
Hi folks,

This is tangential to my post about an internally lighted sign, in which Dean and Douglas
are helping. It appears that we're going to be able to use only about two 48"
fluorescent tubes to not go over the city ordinance for maximum light. This is all very
rough numbers at at this stage. But this sign will be about 4' x 8', and about 9" deep,
making it hard to spread the light out uniformly from only two such lamps.

I divide the world into two types, politicians and scientists. The politician in me says
"don't worry about it, just use multiple tubes to get the even light, and put filters in
to eat up the extra light." But I don't like that side of me. The scientist in me says
to try to do it efficiently.

So I wonder if we can use more tubes, and run them at lower current. It would seem that
some extra inductance in the ballast would give us less current. I think I've read in
Don Klipstein's pages that fluorescents can fail prematurely in such conditions, but I
can't find the reference. Any thoughts on running fluorescent tubes at lower current?
Bad idea? If not, how to go about it.
--
Earl
It's certainly possible to run the fluorescent lamps at lower current; but, yes, do use
enough lamps to light the sign faces uniformly. For whatever lamps you decide to use,
look in the ballast catalogs for the "Ballast Factor" A BF=1 means the ballast will
operate the lamp at full rated current and therefore rated light output (lumens). A
BF=0.9 means the lamps would operate at 90% of rated value. Ballasts are made in several
ballast-factor versions these days.

You can also use circular lamps too, of course, if they match the geometry of the sign
better.

Here's the caution: fluorescent HO lamps and sign ballasts will start and operate the
lamps in cold weather. But, if your sign is located where it gets cold, operating the
lamps at less than rated current also means less than rated watts and therefore less heat
to keep the lamps warm. I've seen some very dim transilluminated plastic signs on cold
winter nights.

For the sign faces, use a good-quality sign plastic such as Plexiglas(R) which is acrylic.
The sign versions are UV stabalized, diffuse the light nicely with minimum losses and
there are lower transmission versions available too. As a rule-of-thumb, the distance
between lamps in a sign can be no greater than 1.5 times the distance between the sign
face and the surface of the lamps if you want even sign face illumination. Also, as a
rule-of-thumb, the optical efficiency of the sign "box" assuming a double faced sign is
about 85% if the interior is painted white. That means 85% of the lumens generated by the
lamps will reach the sign faces (on the inside).

What about the sign content? If you have a highly-decorated sign with lots of lettering,
it's average light output will be less than a relatively plain sign. That's also the way
to reduce the light output of the sign -- add more decoration in the form of a painted
surround or details. However, I think your first priority is to make the sign visible
and comfortable for whomever you want to see it and then worry about meeting the sign
ordinance. The city people are really telling you that they want to see a readable sign,
not a glaring lighting fixture. From a light pollution standpoint, light lettering with a
dark background is far better than dark lettering against a light background and the sign
message is just as visible.

If you have access to a technical library, find a copy of the Illuminating Engineering
Society Handbook, 8th. Edition or earlier (not the current 9th. Edition). There's a
chapter on sign design with all of the design parameters.

Terry McGowan

Terry,

I suspect that white lettering on a black background is not an option from what little I
know of the details of this project. I agree that it looks better that way.

Your 85% figure I'm presuming is just losses inside the box, not counting transmission loss
in the face, and before the lettering is added.

The ballast factor I presume relates to Watts. A 40-Watt tube with a ballast factor of 0.9
would be 36 Watts, etc., and we'd still use a 40 Watt tube.

On Sun, 11 May 2008 03:39:04 GMT, "Earl Kiosterud"

some... at (no spam) nowhere.com> wrote:

[snip]



Terry,

I suspect that white lettering on a black background is not an option from what little I
know of the details of this project. I agree that it looks better that way.

Your 85% figure I'm presuming is just losses inside the box, not counting transmission loss
in the face, and before the lettering is added.

The ballast factor I presume relates to Watts. A 40-Watt tube with a ballast factor of 0.9
would be 36 Watts, etc., and we'd still use a 40 Watt tube.

The ballast factor actually relates to the percent of rated
light output, which roughly translates to power consumption.
You are correct that operated fluorescent lamps at less than
their rated current can damage the electrodes, however, you
should be able to drop the current by 15% to 20% without
significant damage, or you could buy dimming ballasts, which
are designed to heat the electrodes when the current is
reduced, which maintains the electrodes at their proper
operating temperature.

--
Vic Robertshttp://www.RobertsResearchInc.com
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If you have access to a technical library, find a copy of the Illuminating
Engineering Society Handbook, 8th. Edition or earlier (not the current 9th.
Edition). There's a chapter on sign design with all of the design
parameters.