Changing one out of three values in a channel

LIFX color lights have a single channel to manage color, saturation and brightness.

If I have this sitemap entry:

Slider item=Spare_dimmer label="Spare light [%f]"

and this item:

Dimmer Spare_dimmer  { channel="lifx:colorlight:D073D526C30D:color" }

How do I go about connecting the percentage output from the slider to the third of the three values settable in the channel?

Well, I would welcome anyone telling me how to do this, but what I’d really like to know is how to figure this out - I have been going through the docs and examples and forum posts, but I cannot see a way to work out the answer…

You need to link the Channel to a Color Item. A Color Item can be treated as if it were a Dimmer so the only change you need to make is:

Color Spare_dimmer  { channel="lifx:colorlight:D073D526C30D:color" }

OH will know that if you sendCommand a single number to it to adjust the brightness value only. You can put it on your sitemap as a Switch also and the ON/OFF will toggle the light.

https://docs.openhab.org/configuration/items.html#type

and

https://docs.openhab.org/concepts/items.html#a-note-on-items-which-accept-multiple-state-data-types

Thanks - this makes sense. But what if I wanted to send the output of a slider to a specific sub channel?

You would have to create Proxy Items for the channels that you want to control with sliders and use a Rules to change that channel of the HSV values based on the state of the Proxy Item.