Re: Overdriving a light?

["Wayne Jones" <waj at mnsi_net>]

Sam wrote:

Can someone tell me what "Overdriving a fluorescent light" means?

Thanks!

Sam


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It means to exceed the normal operating current of a lamp. This is to
force the lamp to produce more than it's rated amount of light. This
should only be done with an electronic ballast. There is an efficiency
and lamp life penalty for doing this but generally you can also realize
gains in fixture efficiency when lamps are overdriven. For normal lamp
usage where lamps are frequently switched this would be a bad idea but
in aquariums it should not be so bad. High Frequency T8 lamps are
probably the best candidate for overdriving this would include F32 4'
T8s and F17 2' T8s but regular fluorescents will work too.

There is another term called ballast factor that is used to calculate
the light output of a lamp when driven by a particular ballast. When the
ballast factor is 1.0 then the lamp will produce the rated lumens of the
lamp. To determine the actual light you will get from a lamp with any
given ballast you just multiply the lamp lumens by the ballast factor.
Ballast factors much higher than 1.0 can be achieved by overdriving a
lamp. A 4' 32 watt lamp driven by a 4 lamp ballast with a typical .88
B.F. is operating at a current of about 233 mA. If you wire the two
outputs each to two lamps instead of 1 output each to 4 lamps you double
the current going through the lamp which should then be about 466 mA. I
believe this causes the lamp to operate at about a 1.5 B.F.

One way to really use this to our advantage is to buy a double lamp
shoplight that has a one of those narrow reflectors. I see them all the
time at Home Depot. They usually even have a cord and a pull chain swith
on them. You also buy a 4 lamp instant start ballast for 32 watt lamps
then remove the original ballast (which is a piece of crap anyway),
rewire the sockets for instant start and put in either a 32 watt lamp or
a 40 watt 4' lamp. If you use the 32 watt lamps you then have an 8400
lumen fixture. This probably provides about the same light as a 96 watt
PC and costs about $50 USD including the lamps. Here in Canada at least
those 32 watt lamps are very cheap like less than $2 each. YMMV
depending on where you live.

If you do this you will void any insurance that came with the fixture or
the ballast you bought so it is very important that you do not burn your
house down or electrocute yourself or others in the process. I don't
believe it is risky but I am not an electronics engineer either so my
opinion is probably only worth what you are paying for it. I always use
a GFI on my light fixtures so that if anything does go wrong I am at
least protected from electrical shock.

Wayne