People I have known that have designed light faders for light shows have
told me that the brightness change vs phase angle of the AC is very
nonlinear, and that they were never able to get it perceptually smooth with
only 256 steps.  The best designs actually used a look-up table with
12-bit control, but for the PIC, you probably want to do this with an
algorithm to save table space.  Note that changing bulb types and filaments
may make a big difference in linearity/smoothness, and that the eye has a
log response to brightness.

At 05:31 PM 5/1/98 +1000, you wrote:
>I was thinking of using an 'F84 for serial controlled 240Vac lamp dimmer.
>Does anyone know how many steps you need for really smooth fade up/down ?
>