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RDM General Implementation Discussion General Discussion and questions relating to implementing RDM in a product.

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Old November 18th, 2010   #1
mikeb
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Default Tuneable White: Mapping?

Hi!

I would like to implement a dimmer for white light where the color temperature of the white light is changeable within some range (e.g. from 2700K to 6500K).

I think of the following slot assignment:
Slot 1: Intensity 8 bit
Slot 2/3: 16-bit Color Temperature or 16-bit MIREK

There are two principle ways I see:
i) Map to Mirek such as done within the DALI protocol: Mirek=10^6/TC.
1=15.26K 2^16-1=10^6K
ii) Map the 16-bit directly to some temperature range.
0=0K 2^16-1=65535K

Is there already a common way how to map tuneable white?
Is there already a predefined Slot Type (Table C-1) and Slot ID Definitions (Table C-2) for such a dimmer?

I also could not find the unit "Kelvin" within the Sensor Unit Defines, which I require if there is a sensor which measures the current color temperature.

Thanks for your comments,
Mike
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Old November 18th, 2010   #2
sblair
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Hey Mike,

I've never actually seen or heard of MIREK before. Typically I just see CTO and CTB correction slots being used. There is a defined
SD_COLOR_CORRECTION slot descriptor. If you needed a different one that is more specific it can easily be added as the Slot Definitions are extensible via the ESTA website to make it easier to add additional slot definitions.

The only temperature unit defined is in Degrees Centigrade. I appreciate that Kelvin makes a LOT more sense when discussing Color Temperature. This has been a topic that has been coming up a lot lately in regards to Sensor units. I'll put Kelvin in the list of ones we should add in the next revision, but it will probably be a while until we get to that point though as the last revision is still in the final stages of getting published.

You can also use a UNITS_NONE and then put "Kelvin" in the sensor name description though and then generally conveys it correctly to the user.




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Old November 18th, 2010   #3
ericthegeek
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Quote:
Originally Posted by mikeb View Post
There are two principle ways I see:
i) Map to Mirek such as done within the DALI protocol: Mirek=10^6/TC.
ii) Map the 16-bit directly to some temperature range.
In general, DMX values don't represent any real-world values. Most manufacturers just make 0 be the lowest output they can physically create, and 65535 be the highest, with some kind of linear or proportional scale in between. There's no reason to make the DMX value of 1000 match a particular Mirek, or any other value.
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