That is somewhat of a broad question.  Most light sources
except for incandescent bulbs can be modulated.  Even incandescent
bulbs can be modulated, but they can't change brightness fast enough
to produce much audio.

        Most of the schemes I know anything about for sending audio
over light involve using a fluorescent tube or even a LED since those
light sources are much faster at responding to changes in electric
current than are incandescent lamps.

        The LED or fluorescent lamp is run at some frequency which is
way too high to hear.  That carrier is then frequency-modulated.  A
receiver need only have a photo detector capable of decoding the
carrier.  The rest of the receiver could be any FM radio once the
photo cell receives the carrier.

        It is even possible to modulate an infrared LED with
a fast-enough stream of digital data to cary audio and even voice.
That is how the photo detector works in your CD player to begin the
process of turning a flashing stream of light in to music.

Martin McCormick

Jim Stevenson writes:
>From light bulbs to lasers to ir devices,
>what equipment can modulate them with voice?
>
>a.m or f.m?
>
>Thanks much again as always.
>
>73
>wb6 yoy
>
>(650) 604-5720
>