On Thu, 3 May 2012 20:20:10 -0700 (PDT), ColdFusion
Post by ColdFusion
I know that mercury arc actually becomes about 10% more efficient when
it is operated on high frequency. I believe it has to do with the arc
not extinguishing at zero crossing as it does on sinusoidal operation
on line frequency.
Low frequency square wave is utilized for filming video to avoid
flickering as well by electronic HID ballast as HIDs can not tolerate
high frequency operation.
If fluorescent lamps were to be operated at 60 or 400Hz square wave,
would it provide 10% gain? How about lamp life? Since with square
wave, the peak and RMS are the same, I would think that it would
provide a LCCF of one which should be beneficial to lamp life.
Sorry, I've been away too long.
I a 4-foot, T12 fluorescent lamp, the lamp used most often for high
frequency measurements and modeling, the gain from high frequency is
about 10%, and half of that, about 5%, comes from a decrease in
electron density modulation, while the other half, another 5%, comes
from a decrease in anode fall losses at high frequency. Nine of the
gain is due to "starting" but I think you mean the modulation of
So, if you run this same lamp at DC, that will give you a 5% efficacy
gain. There was an excellent paper published in 1972 by Drop and
Polman at Philips that shows this effect. I will try to post that
later today. A square wave will be like DC as far as the electron
density is concerned.
Since part of the gain comes from a reduction in end losses, the anode
fall, you can see that the high frequency efficacy gain is a function
of the lamp voltage (length). An infinitely long lamp would have a 5%
gain, because the reduction in end losses is insignificant. A short
lamp, such as a 2-foot, T12, would have a greater gain, about 15%,
because the importance of the end losses is double.
sci.engr.lighting Rogues Gallery http://www.langmuir.org
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