Re: Three lighting questions

["Wayne Jones" <waj at mnsi_net>]

Gordon wrote:

If you have a lot invested in F40T12's, the b432 will run them, but a
single
circuit will not provide enough power for max brightness, however 2x
circuits
will provide plenty, and three or more might produce more light, and
will
deffinately produce more heat, as well as shorten the lifespan of the
bulb...
The problem I've found with the t12's is a short life span even at
normal
output (NO) (my f40t12 pl/aq's only lasted about 5mo before fading)

T8's are much newwer technology and have a greatly improved lifespan...
They
are a bit harder to find in pleasing colors for aquarium use however.
------------------------------------------------------------------------
--------

Nice post. That pretty much covers it. I have been playing with a meter
and a 4 x 32 ballast and I have made some interesting observations. My
meter is unable to read the current output of this ballast but it can of
course read the current input. It can also read the voltage across the
lamps. By assuming the ballast losses remain at a constant 4 watts I can
therefore guess the wattage output of the ballast.

One thing that suprises me is that the more current you put through the
lamp, the lower the voltage gets across the lamp. I presume this is
because when more current is pushed through a lamp it becomes a better
conductor and it's resistance probably drops. What this means is that
this ballast does not overdrive lamps nearly as much as one might think.
2x driven 4' T12s are hardly being overdriven at all. I can also roughly
measure the light output of the lamp with a digital camera. It turns out
that overdriving does lower the efficiency of the lamp but much like PCs
not as much as you might think. According to my admittedly crude
measurements a 32 watt T8 has a ballast factor of about 1.4 when
overdriven by 2x. I am going to do this again with a better light meter
and will post the results. Without the ballast factors it is very hard
to know whether overdriving is truly worth it. I think it is but I want
to know the efficiency of the system and the ballast factor of the
system. In the case of the original post, this means that 4 2x driven 32
watt lamps will produce about 15,600 lumens. Pretty good for a $60
investment and very little work. The T8s have the added bonus of
improving fixture efficiency as well.

Those plant and aquarium lamps are notoriously shortlived. You can buy
lots of 40 watt t12s with 20,000 hour lifespans. 40 watt T12s are not
designed for instant start though and that could be part of the problem
as well.

Wayne