Re: Light bulb power control/dimmer

In article <s701j.20108$4k.13529@xxxxxxxxxxxx>, LVMarc wrote:
Spehro Pefhany wrote:
On Sun, 18 Nov 2007 17:16:22 +0000 (UTC), the renowned
don@xxxxxxxxxxxxxx (Don Klipstein) wrote:

In article <pan.2007.11.16.21.28.25.395724@xxxxxxxxxxx>, Nobody wrote:

On Fri, 16 Nov 2007 10:55:56 -0500, Tam/WB2TT wrote:

Remember, with cycle skipping the frequency changes. At 10 percent power the
fequency would be 6 Hertz.

The flicker will be 12 Hertz (as opposed to 120Hz at full power). You
don't have to skip whole cycles; half-cycles will do. The polarity doesn't
matter for a resistive load.

In extreme cases, I have seen incandescents visibly flicker from
skipping every other half cycle. The main example is a 4 watt or 7 watt
120V incandescent nightlight with a diode. The thin filament warms and
cools fast enough to have significant 60 Hz flicker. 60 Hz flicker is
sometimes visible.

- Don Klipstein (don@xxxxxxxxx)


Yes, you can't practically dim an incandescent bulb by skipping
cycles. I tried it many years ago and the results were miserable.
Maybe if you had control over the bulb design and could add some
thermal mass to the filament, but I tried it with a huge incandescent
(kW, IIRC) and even that thick filament responded too fast. I used
some kind of clever (I thought) CMOS circuit (I forget the details)
using something like a rate multiplier to get a relatively fast cycle
time (eg. 50% would be a 30Hz cycle). OTOH, it worked a charm on
relatively fast-response heaters for tight temperature control, which
was the intended purpose.


Best regards,
Spehro Pefhany


The persistence of vision, the flicker frequencies for most folks is
about 8hz, so when the proportion f 1/2 cycle arpoaches that some folks
will begin to see it, and other will not, as you eat more cycles of
course the drive is more choppy and you cant average out the photons as
the other poster noted :-)

I remember an electrical engineering lab day in college many years back.
One thing to be tried was to adjust the horizontal sweep rate of an
oscilloscope to the point where with no vertical signal the trace barely
did not visibly flicker. Maybe sweep was triggered externally, because
this was to determine sweep repetition rate for the trace to borderline
visibly flicker and not flciker.

Most of my classmates got frequencies in the 40's and low 50's of Hz for
this.

- Don Klipstein (don@xxxxxxxxx)
.

Relevant Pages

  • Re: Light bulb power control/dimmer
    ... The flicker will be 12 Hertz. ... skipping every other half cycle. ... 120V incandescent nightlight with a diode. ...
    (sci.electronics.design)
  • Re: Light bulb power control/dimmer
    ... The flicker will be 12 Hertz. ... skipping every other half cycle. ... 120V incandescent nightlight with a diode. ... dbe bad on a light bulb load, with a slight, very tiny mathemical sized ...
    (sci.electronics.design)
  • Re: Light bulb power control/dimmer
    ... The flicker will be 12 Hertz. ... skipping every other half cycle. ... 120V incandescent nightlight with a diode. ... Maybe if you had control over the bulb design and could add some ...
    (sci.electronics.design)
  • Re: Light bulb power control/dimmer
    ... The flicker will be 12 Hertz. ... skipping every other half cycle. ... 120V incandescent nightlight with a diode. ...
    (sci.electronics.design)
  • Re: Light bulb power control/dimmer
    ... I have seen incandescents visibly flicker from skipping every other half cycle. ... The main example is a 4 watt or 7 watt 120V incandescent nightlight with a diode. ... Don Klipstein ...
    (sci.electronics.design)