2nd draft: Fluorescent Article

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, 
clarifications, etc.

Ian Philips

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.
         Cheaper bulbs.

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. 

Lumens depreciation
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 

Design lumens
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 
"burn-in" period.

Ballasts types
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.

Lamp life
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.

Shop lights
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 
normally should.

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 
public library.