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

[Marc_F_Hult <MFHult@xxxxxxxxxxxxxxxxxxxxx>]

On Wed, 1 Nov 2006 09:24:03 -0700, "Jon Woellhaf" <jonwoellhaf@xxxxxxxxxxx>
wrote in message  <GPOdnU8CbooHV9XYnZ2dnUVZ_tidnZ2d@xxxxxxxxxxx>:

>"Marc_F_Hult" wrote
>> ... folks that are interested in _actually_ dimming TRIACS,
>> back-to-back SCRs or SSRs based on them may be interested in a spreadsheet
>> that I created about 5 years ago.
>>
>> http://www.econtrol.org/dimmers/TRIACDimmerCalcs_MFHult.pdf
>> ...
>
>Thanks for posting this information. I found it very interesting.
>
>In dimming lights in a home, theater, etc., doesn't the human's non linear
>response to light intensity need to be considered?
>

I presume that you are asking about the part of the spreadsheet that predicts
the Percent Luminous Intensity of dimmed compared to undimmed. Note that the
units are in are percent (%). So what this predicts (eg) is that the luminous
intensity of two lamps dimmed to 50% (accomplished by turning the TRIAC and
lamp on at 76 degrees = 3.5 milliseconds after zero crossing) would be equal
to the luminous intensity of one lamp that is undimmed.

Human sensitivity doesn't enter to the calculation. Luminous intensity has
units of candela (previously candles) and is 1/683 watt/steradian for one
particular, specified  monochromatic light. One can convert to lights of
different wavelengths using the CIE photometric curve.

Note too that the equations, graphs and table don't predict/calculate the
reduction in color temperature with reduced rms voltage. That's yet another
phenomena requiring a different equation (approximation).

Human sensitivity _would_ be a useful thing to account for depending on the
application. As a practical matter, that's what one accounts for manually 'by
eye'. One purpose of the dimmer curves is to create a response such that the
adjustment range of a slider (on a pro lighting console) or a knob (on a
wall-mounted household dimmer) is not too cramped in some places and too
insensitive in others.

With computer control, they can be used to create look-up tables to relate all
manner of things one to another empirically (by previous direct measurement).
So for example, one could create a look-up table that would make each, say,
1/8 turn seem 'twice as bright' as before (whatever 'twice' might mean to
you.. .)



... Marc
Marc_F_Hult
www.ECOntrol.org