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Possible to run fluorescent on lower current?

E

Earl Kiosterud

Jan 1, 1970
0
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.
 
D

Don Klipstein

Jan 1, 1970
0
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.

Another idea: Get a bunch of the 25 watt or whatever is the
most-reduced-power version of F32T8. Get a ballast rated to handle
perhaps 4 of them with ballast factor on the low side. You should be able
to get even light without having to "eat" as much light, and use not too
much more power than with two "more normal" 4-footers.

One more idea: Add diffusing filters to make the light more even. You
probably don't need to worry if you add a bit of loss here if you combine
this with upping the lamp count.

- Don Klipstein ([email protected])
 
T

TKM

Jan 1, 1970
0
Earl Kiosterud said:
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.
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
 
E

Earl Kiosterud

Jan 1, 1970
0
TKM said:
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.

Thanks so much for some useful info and good tips. I don't know much of the details of the
sign. It's Pete's first illuminated sign, and I got involved to help with the light issues,
partly because I've always needed to take the time to understand lumens, candelas,
foot-candles, etc.. I'll pass all this on to him.

I'm still trying to understand why 34,400 lumens doesn't work out to 4.38 foot-candles at 25
feet. I have that in another post.
 
J

John D. Bullough, Gurley Building

Jan 1, 1970
0
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.

The "Lighting for Advertising" chapter of the Handbook was combined with
the chapter on "Retail Lighting" in the 9th edition, so the sign stuff is
still available in the latest edition, it's just the second half of the
retail lighting chapter.
 
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