2nd draft: Fluorescent Article
To: Aquatic-Plants at actwin_com
Subject: 2nd draft: Fluorescent Article
From: "ian (i.b.) philips" <ianphil at bnr_ca>
Date: Thu, 14 Dec 1995 15:33:00 -0500
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This is a second draft of the article which I (ahem) "wrote". It has been
shorten, tightened and incorporated comments that were made on the first
draft. Thank you for your input. I feel a little bad that I have removed
all attributions to contributors (and there were many). I hope no one is
offended. It was easier to tighten it by doing that. I'm sure people will
recognize certain paragraphs as their contributions. I hope you don't
mind me doing this. I just want to present the facts on fluorescent lamps
and ballasts for the benefit of all.
Again, any comments are most welcomed, especially corrections,
Fluorescent Lamps and Ballasts
by Ian Philips
There has recently been a lot of discussion on the "Aquatic Plants Digest"
about fluorescent lighting and T8 vs. T12 bulbs. I thought that a summary of
the discussion would be of value to our aquarium society members. I have
distilled many postings down to a unified article. The bottom line was that
people who have tried both types of lamps prefer:
T8 bulbs in combination with an
Electronic rapid start ballast.
The benefits being:
Longer bulb life with lower lumens drop off.
Significant power ($) savings.
Differences between T8 and T12 lamps
T8's are 1" in diameter, T12's are 1 1/2". T8's run on an electronic ballast,
and will not run (efficiently) in a fixture with a regular ballast. The same
length of lamp also runs on less electricity, a four foot T8 is 32 watts,
while the four foot T12 is 40 watts.
The commercial lighting industry is rapidly shifting towards the more energy
efficient T8 bulbs. The driving force in the US are the new US Federal Minimum
Energy Standards for fluorescent lights. The old F40T12CW cool whites will be a
thing of the past.
Relative amount of light
Bulb for bulb, T8s give the same amount of light, or possibly slightly more,
as equivalent T12s. According to the "Philips Lighting Guide to Fluorescent
Lamps" for comparable 48" lamps, a T8 produces 2600 "design lumens" versus a
T12's 2520 "design lumens". However, the T8 does this using 32 watts versus
the T12's 40 watts. So while a one-for-one replacement of T12s with T8s won't
necessarily increase your lighting it will lower your electricity bill.
All fluorescent bulbs dim as they get older. The rated lumen depreciation of
T12 fluorescents is about 10 percent after 3,000-4,000 hours of operation and
20 percent after 7,000 hours, while for T8 lamps, running off electronic
ballasts, the loss is even slower, 10% total after about 7,000 hours of use.
That's a two-year period if the lights are on 10 hours a day. One reason for
the T8's lower lumens depreciation is the use of the electronic ballasts. It
is reported that conventional ballasts cause increased lumens depreciation.
Some people are suspicious of the lumen depreciation because they don't see
commercial places replacing their banks of lights every six to twelve months.
The reply to this is that the human eye is a very poor judge of brightness.
As long as the ambient light level is adequate for whatever activity is taking
place, the lighting is "fine". Most homes or offices don't replace bulbs
until they burn out or start to flicker, while some places do perform regular
All fluorescents have a "burn-in" period, during which they are much brighter.
This burn-in period isn't exact, but their lumens decrease at a high rate for
a short time, then settle in to a steady, lower rate. Fluorescent specifica-
tions normally give both "initial lumens" and "design lumens". Thus side-by-
side comparisons of lamps should be made after they have passed their
The Time-Life book "How Things Work in Your Home (and What to Do When They
Don't)", contains one of the better descriptions of fluorescent lights. It
explains that there are three types of starting technology. (1) Preheat where
an auxiliary starter is used to heat the tube ends and strike an arc across
the tube. (2) Rapid start where a special ballast applies a relatively low
voltage directly to special, quick-heating cathodes (tube ends). (3) Instant
start where the ballast supplies a voltage spike of a magnitude up to 4 times
the normal operating voltage of the bulb.
Another factor affecting lumens and power consumption is the "ballast factor".
"The ability of a ballast to cause a lamp to produce a percentage of its
initial rated lumens is called its ballast factor." Magnetic ballasts have
a bf less than 100 percent while electronic ballasts can have a bf of more
than 100 percent. This is another reason why T8 / electronic ballast combina-
tions give more light for less power.
Most aquarium hoods are of the preheat type. Shop lights and most 40W systems
are of the rapid start type, which Time-Life says requires special cathodes in
the bulbs. Bulbs with single pins are instant start.
According to the Valmont Ballast technical guide, short lamp life (which may
be different than reduced lumens) is attributed to:
1. Improper voltage
2. Improper wiring
3. Poor lamp to lamp holder contact
4. Extremely short duration cycles (many lamp starts per day)
5. Defective starters (applies only to preheat)
6. Defective lamps
7. Improper ballast application
8. Defective ballast
In the "Philips Lighting, Guide to Fluorescent Lamps" there is a graph that
shows average life for a variety of different fluorescents based on burn hours
per start. Double the bulb life expectancy (in thousands of hours) is possible
with a 12 hour burn cycle as with a 4 hour burn cycle. Fluorescents are usually
rated on a cycle of 3 hours on and 20 minutes off.
The following is a quote from the same text: "Longest lamp life and best *lumen
maintenance* (our emphasis) will be obtained with 1) good voltage, 2) proper
auxiliaries, and favorable operating conditions such as are ordinarily
encountered in a well-designed lighting system".
"The Lighting Management Handbook" by Craig DiLouie gives additional
information. Operating temperature affects fluorescents. The light output of
fluorescents peaks at 77F. Higher temperatures greatly reduce lumen output
and lamp life, with a 10% loss from peak at 100F. The lesson here seems to
be to try to keep our lamps as close to 77F as possible. High-output lamps
seem more sensitive to higher temperatures as their light output peaks at
60F. At 100F, their light output is down almost 20% from peak.
Lamp/ballast combination also plays a role. For best lumen output and lamp
life, the lamp needs to be matched to its ballast. With all the different
types of ballasts and lamps, who really knows whether their combination is
optimal. Note that there are instant start and rapid start circuits for both
electronic and magnetic ballasts. An instant start on an electronic ballast
can cut lamp life in half.
The experience on "the net" with the inexpensive shop lights has not been
good. The fixtures are not especially long lived, and even worse, they appear
to burn out bulbs faster than normal. This was reported by two people who had
shop lights burn out tritons and vitalites in less than one year. It has also
been reported that bulbs in shop lights do not produce as much light as they
Converting shop lights
Fortunately, converting shop lights to use T8 bulbs is relatively simple.
Both types use the same lamp holder. All that is required is to replace the
ballast in the shop light with a T8 rapid start ballast.
Most fixtures are held together with screws. Just remove the screws. The
ballast is in the space above the bulbs if the fixture is right side up.
When you have it upside down to work on it, the ballast is under the reflector.
There is normally a schematic drawing right on the ballast, and the wires are
usually the same on the old ballast as on the new one. Mark all connections so
you'll know how to put it all back together. That's all there is to it!
Compared to the price you can get T12 cool white and warm white bulbs for,
T8 bulbs are more expensive. However when you compare the specialized spectrum
bulbs, T8s are cheaper. Specific prices depend upon where you are. Call
suppliers in your area and find out specific prices for bulbs and ballasts.
Another point to consider, while the specialized T8s are a couple of dollars
more expensive than the ordinary T12s, due to the cheaper operating costs and
longer life, T8s end up saving money in the long run. I leave the
calculations to others.
The references used by the people on the net include "The Lighting Management
Handbook" by Craig DiLouie, a technical guide to retrofitting lights to save
energy, the Time-Life book "How Things Work in Your Home (and What to Do When
They Don't)", the "Valmont Ballast Technical Guide", and the "Philips Lighting
Guide to Fluorescent Lamps". You can find other similar references in your