Re: T8 benefits

["Wayne Jones" <waj at mnsi_net>]

Sam wrote:

Where do the benefits of T8 lighting come from, the ballast or the bulb?
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You have hit on an issue that seems to be widely misunderstood in our
circles. The primary benefit is from the ballast but the small lamp
diameter improves fixture efficiency and the high frequency type T8 (F32
lamps for example) do operate at slightly better efficiencies.

Sam wrote:

For instance:

T8's are brighter because the phosphor doesn't get a chance to dim as
much
because of the 20,000 htz cycle (opposed to T12 magnetic ballast's 60
htz)

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True, but all T12s can be run on electronic ballasts as well with
similar increases in lamp efficiency and ballasts efficiency. The
interesting thing here is that the main benefit that electronic ballasts
provide is that they actually alter the efficiency of the lamp itself.
This sort of leads to confusion over the efficiency of T8 lamps.
Manufacturers usually provide lamp data for T8 lamps based on operation
on electronic reference ballasts making those lamps appear to be very
efficient. T12 lamp data is derived from operation on magnetic
electronic ballasts so naturally those lamps appear tobe much less
efficient.

Sam wrote:

T8's decrease only to 90% inital lumens whereas T12 goes down down
down....

T8's last 20,000+ hours. Since the real lumens stay at 90% of the
initial
lumens you'll actually get 20,000 hours of use instead of T12's 6
months.

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This is generally true but not entirely so. The best high frequency T8s
have 95% lumen maintenance and last well over 20,000 hours but these
days most T12s do last 20,000 hours as well. Lumen maintenance is
generally not as good but even VH0 T12 lamps have been greatly improved
in this regard using the same lamp coating technology as used in T8 and
T5 lamps.

Sam wrote:

T8's are made with newer tri-phosphor coatings whereas T12 isn't - does
that
matter?

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This one is basically not true. You can get virtually the same
triphosphor phosphor in T12s as in T8s. They do not appear to be
absolutely identical but perform in very much the same way.

Sam wrote:

So what gives these beneifts, the bulb or the ballast? Are the benefits
really from the electronic ballast regardless of the tube type?

If you overdrive a T12 bulb with a T8 ballast will you get the same
benefits
of a "T8 bulb setup?" My problem is that T8 bulbs are in  short supply
where
I live for the different spectrums. My choices are (better sit down this
is
pretty long): 3000k 72CRI or 4100k 82CRI. =) I can mailorder but if I
can
get the same benefits with a T12 bulb I'll stick with them.

I overdrove a T8 light X4 with a T8 ballast and compared it to a 8 month
old
abused T12 bulb powered by the same ballast (also overdriven X4) and the
T12
bulb looked brighter. The T8 looked bright as heck on the ends but dim
in
the middle.
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An electronic ballast improves lamp efficiency by about 15%. High
frequency T8 lamps are about 5% more efficient than T12 lamps and have
better lumen maintenance.  Personally I believe that HF T8s are the way
to go but I am not sure. The small diameter is a major benefit in most
aquarium fixtures especially if you have a fairly deep tank and
overdriving appears to be much more effective with an HF T8 lamp.
Choice of lamp spectrum though is a really big downside though. You can
also get regular T8s in 4' 36 watt or 40 watt. These lamps are sold all
over the world but not so much in N. A. They are actually identical
lamps but to avoid relamping confusion they are labelled differently for
different markets. These T8 lamps have the same operating
characteristics as T12 lamps of the same length. You get the same
improved fixture efficiency but not the slight increase in lamp
efficiency. These lamps on an electronic ballast might be the best
choice if they were not so expensive in N.A.

I have been busy testing different lamp combinations and estimating lamp
power consumption. If you overdrive a 4' T12 4x or a 4' T8 4x the lamps
operate at exactly the same wattage of about 64 watts. Soon I will have
a good setup for measuring light levels but until then I can't be sure
of how much more light each lamp is providing.

I also tested overdriving a pair of 2' lamps on a 4 x 32 watt ballast.
To my suprise it made a huge difference as to which way I went about it.
2 F20s overdriven 2x were driven at about 20 watts but a pair of F20s in
series overdriven 4x were driven at about 34 watts.  Overdriving is a
trade off betwen lamp efficiency, lamp intensity and lamp life. I very
much doubt that when the lamp cosumes 34 watts that this means you are
getting 70% more light but we need to know what we are getting to make
reasonable decisions on lamp choices and overdriving choices. This one
ballast has well over a 100 possible lamp and wiring possibilities so it
is going to take a while to do this.

I think electronic ballasts though are a no brainer. You really can't
lose. More intense light output with the same lamp, better lamp
efficiency with the same lamp and a huge advantage in versatility.

Wayne