Date: Sat, 31 Jan 1998 22:26:23 -0800 From: Denis Daly <dalymob@bigpond.com> To: cp@opus.hpl.hp.com Message-Id: <aabcdefg412$foo@default> Subject: Flourescent Lights and possible Danger to those who fiddle
Charles
I note Phill's advice that you can get cheaper light fittings in
UK from an electricians supply shop.
You can do so in Australia also but:-
It might be worth considering whether fluorescent lights
provide sufficient light for your needs. You might need a high
pressure discharge lamp of 400 to 1000 watts to provide sufficient
light for your plants.
You may be able to compensate for reduced lighting by using carbon
dioxide at 1000 ppm in the atmosphere (instead of the usual 300
ppm). However as 5000 ppm of carbon dioxide can kill you it is not
advisable to try this indoors, particularly in homes that are
tightly closed up in the winter.
Perhaps a determination of actual lighting intensity required for
various plants should be decided upon first. (I really can't help
as in Sydney, Australia all my plants are outdoors all year.)
Adapting commercial fluorescent fittings:-
There is an important aspect associated with adapting electrical
appliances rather than just buying them. That is you must know
enough about electricity to do it at all and to do it safely.
Lack of knowledge of the electrical theory and electrical
installations in the
USA (or indeed in any country) could cause you to waste your money
or, as you fiddle with the fitting, to kill yourself or a loved
one.
It is difficult to go into the exact details as I do not have
intimate knowledge of the USA electrical installations but I hope
that amongst the many members of the list there is an US
electrician who could elaborate on the specific practical details
as they apply in the USA.
To start the "ball rolling" I present the most likely possible
scenarios below:-
If the following bores you then I apologise.
But if you do not understand all of it then you should not fiddle
with electrical equipment.
Even if you understand it you cannot assume that all members of
the digest do.
The single phase voltage in UK and Australia (and, I believe in
most countries) is between 220 to 250. It varies country to
country. There is an international standard
agreement to go to 220 volts eventually.
The fluorescent lights sold for use with phase voltages of 220 to
250 volts can be effected cheaply as there is ample "spare"
voltage available to enable the current limiting function of a
ballast and to "strike" the "warmed" tube by adding the back
voltage of the ballast to the supply voltage as the starter opens.
This type incorporates a thermal starter which flicks on off to
induce a back voltage (generated in the ballast inductor) which
adds to the voltage to the mains supply to fire the tube. The
starter keeps flickering until it "opens the circuit" at a time
near enough to the peak of the AC (sinusoidal Alternating Current)
wave so that a sufficient voltage to fire the tube is generated.
While the starter circuit is closed the filaments of the tube are
being heated to reduce the tube firing voltage required.
Once the tube has "fired", the ballast acts as a current limiter.
Without the ballast to limit the current (as the tube's resistance
falls instantly as it gets hot) once the tube fires it would blow
up in milliseconds and bits of glass would be propelled about the
room.
As I understand it the single phase voltage (in the power point,
power outlet, appliance socket, or whatever else you call it) in
USA is 110 to 120
volts.
Fluorescent lights for 120 volts would need to incorporate a "step
up transformer":-
This could be implemented in one of two ways:-
1) "instant start" . (i.e. no flickering to start)
As there has to be a step up transformer to provide the "spare"
voltage, the step up transformer's "open circuit" output voltage
is made to be several hundreds of volts initially to "fire the
tube" without using a starter. (This is sometimes called cold
start as the tube filaments are not heated to assist starting.
Hence the firing voltage must be several hundred volts.)
Then the magnetically leaky transformer (between the primary and
secondary windings .... designed to be so) causes the loaded
output voltage (fictional point in electrical circuit theory which
makes the maths easier) to drop to around 200 volts, while the
impedance of the secondary winding limits the current through the
fluorescent tube. (Step up transformer and ballast inductor are
magnetically interconnected and in the one can.)
("Instant start" or "Cold Start" types are sold for 220 to 250
volt supply also.)
2) Alternatively you might find that a 110 - 120 volt fluorescent
light fitting has a
step up (to around 220V) transformer fitted as well as the current
limiting ballast. This transformer would not be magnetically leaky
and would be a separate unit magnetically, even though it might be
in the same can as the ballast. The ballast starter combination
generate the firing voltage. This type flickers when first
switched on.
(Some more modern, 110 to 120 volt, fluorescent ballasts may be
"electronic" but they will still need to "step up the voltage" to
fire the tube and provide some "spare" voltage across their
current limiting circuitry.)
In large scale industrial or commercial lighting installations the
premises would probably have its electrical load spread over two
or three phases. (I won't elaborate on what a phase is. It would
take me all day and confuse you.)
While I don't know what is actually done in the USA I suspect that
commercial light fittings may be wired across two phases (of a 3
phase system) thus operating on (square root 3) x 120 volts =
1.732 x 120 = 207 volts (1.732 x 110 = 190 volts). While the
ballast (inductor, choke) would be different than that for 220 to
250 volt use, it is possible to use the simpler (and cheaper)
ballast with thermal starter and without a 110 to 220 volt
transformer in each light fitting.
Thus if you buy a commercial type fitting in the USA it may not be
able to be used in your home simply plugged into a 110 volt power
outlet. In the USA it may be possible to have a two phase 220V
power outlet installed in your home. You could buy a 110 to 220
volt transformer large enough to run several lights. But in some
remote rural locations there may only be a single phase supply
available.
The fact that the USA uses 60 Hz vrs 50 Hz frequency of
electricity
does not affect the above voltage considerations. It does have an
effect on the design of the components used though.
You need to consult an electrician or a friend who has electrical
knowledge to determine what is going on. It's not possible for me
to do so from Australia. The point is you need expert advice in
the USA. Perhaps there is a requirement to be licensed to work on
electrical installations in the USA. There is in Australia.
Sorry about the complication but I felt compelled to warn you.
Electricity can kill you if you don't know what you are doing.
Consult an expert.
There are other special types of fluorescent lights, including
battery operated and those with electronic drivers. I did not
address these matters as I presume that what you seek are cheap,
reliable lights.
Even battery powered fluorescent lights generate dangerous
voltages inside.
High pressure discharge lamps also present the same minimum supply
voltage problems as do fluorescent tubes as I outline above
Regards
Denis Daly
dalymob@bigpond.com
(There is no .au on the end. Yes it is in Australia.)
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