Re: TRIAC dimmer control spreadsheet; was Re: Controlling Holiday Lights

[sylvan butler <ZsdbUse1+noZs_0611@xxxxxxxxxxxxxxxxxxxxx>]

On Thu, 02 Nov 2006 15:38:23 -0500, Marc_F_Hult <MFHult@xxxxxxxxxxxxxxxxxxxxx> wrote:
> On Wed, 1 Nov 2006 15:04:00 -0700, sylvan butler
><ZsdbUse1+noZs_0611@xxxxxxxxxxxxxxxxxxxxx> wrote in message
><slrneki6eg.a7n.ZsdbUse1+noZs_0611@xxxxxxxxxxxxxxx>:
>
>>On Wed, 1 Nov 2006 09:24:03 -0700, Jon Woellhaf <jonwoellhaf@xxxxxxxxxxx>
> wrote:
>>> In dimming lights in a home, theater, etc., doesn't the human's non linear
>>> response to light intensity need to be considered?
>>
>>As Robert posted, the "practical" way is to just set the light level you
>>prefer.  It doesn't really matter if the dimmer is passing 80% or 20%,
>>just so long as you can set it to get what you want.
>
> This certainly applies to the end user. But folks that actually design dimmers
> might initially choose a mathematical representation of the known physics for
> design purposes. (I got the equations shown on my spread sheet from Chris

yeah, back in the days when the dim level was controlled by a variable
resistor (even when controlling a triac) it was handy to know the value
of that resistor and the floor and ceiling values of the total
resistance.

> From my  at http://www.econtrol.org/dimmers/TRIACDimmerCalcs_MFHult.pdf
>
> 50% dimming with respect to luminous intensity is achieved at ~76 degrees =
> 3.53 milliseconds delay.

And that will vary somewhat depending on differences in the actual
incandescent light (hardware).

> But in the case of TRIAC dimmer control (see thread subject) a single byte
> holds all the information needed to produce 2^8 = 256 levels

An 8-bit byte always does.

> by creating complex waveforms with large data requirements that by his
> admission challenges the timely computing power of a PC.

Marc, I neither said nor alluded to any such thing, and I thank you
kindly to not put words into my mouth.


> Applying 'perceptual coding" to that single 8-bit byte, we could usefully
> 'compress' it to a 4-bit nibble to produce 16 levels if that is all that is
> needed.


That is not perceptual coding and is not in any way related to it.


> can be used to select values for a new, equal intensity, 16-step dimmer curve
> with Full ON, Full OFF and 14 intermediate steps each causing about 6%
> reduction in light intensity.

You certainly do not want "equal intensity" and equal "6% reduction in
light intensity" in your steps.  If you actually implemented a dimmer
that way, the bottom steps (starting from dark) would appear
significantly bigger jumps than the top steps (approaching full-bright).
THAT is human perception.

Perceptual coding takes place at a lower level in the design, realizing
that human vision can detect a very small change from dark (no lumens)
to some light (lumens), but cannot detect an equal change in lumens from
bright to brighter.  Thus perceptual coding is used so that whether your
dimmer has 16 steps or 256 steps or 65536 steps, the perception of
brightness is uniform at each step even though the increase in light
intensity between each step grows MUCH larger as the light gets
brighter.

sdb

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