i was trying to determine the best mechanism of light production. with 
a dc supply, the conductor would get hot and incandesce producing photons 
of various frequencies up to its melting point. however, the conductor 
will also generate an electromagnetic field. this field has a range 
related to the voltage applied to the conductor. another conductor 
moving through this field will experience induction and generate 
electricity. if the first conductor is switched on and off, this will 
generate an em wave which will induce current in the second conductor. 
i am trying to determine wether a dc current or an ac current will 
generate light more efficiently for communication purposes. and is the 
range of frequencies produced not limited by the melting point of 
materials? what is the lowest and highest frequencies currently 
possible? also, if the range of the electric field is limited by 
voltage then how are em waves broadcast over infinite distances of 
space?

That's a lot of questions, but let me answer some of them. An
incandescent light source is very efficient at converting electricity
into heat to raise the temperature of the filament. It is inefficient
at converting that heat into visible light because it creates a
thermal distribution of wavelengths that contains most of its power
outside the visible range, particularly in the infrared. The hotter
you run it the better, but if it runs too hot, the filament doesn't
last long. You can do a little better with a halogen bulb, which
prolongs the life of the filament and allows you to run a little
hotter.

It is slightly more efficient to use DC since the temperature of the
filament will always be at its highest point, but this is a small
effect since the thermal time constant of the filament is typically
long compared to half a cycle of AC. You can safely ignore the 60 Hz
radiative losses that you are worried about since these will be tiny
compared to the total power. If those losses were important, you could
always use two filaments in close proximity, with the currents flowing
in opposite directions to drastically reduce the 60 Hz radiated field.

For better efficiency, you need to abandon incandescent light in favor
of flourescent lights. Light emitting diodes are also getting better
every year and are the most efficient way to produce colored light.
Someday they may surpass flourescents in efficiency at producing white
light.

For communication purposes, lasers are typically used. A semiconductor
diode laser can have very high efficiency (better than non-lasing
LEDs). It is also highly directional so it is much better than any
other light source for communication.

The range of frequencies produced by an incandescent filament is not
strictly limited by the melting point, but the distribution of power
over frequency is. You can run it hotter and hotter, shifting the peak
of the emission spectrum higher and higher until you melt the
filament. You will still have power in the ultraviolet, even if the
peak is in the infrared, but the hotter you run it, the more
ultraviolet you will get. As mentioned above, halogen lamps can run
hotter and thus produce light with a slightly higher frequency peak in
the emission spectrum.

I have no idea what you mean by the range of the electric field being
limited by voltage. The voltage only affects the amplitude of the
emitted radiation. The radiation still propogates to infinity
following the inverse square law. If you are twice as far away the
electric field will be reduced by a factor of two and the intensity or
power will be reduced by a factor of four.