color temperature control

[tazztone]

guys. as you might know there are these (cheaper lm/$ than most COBs) Bridgelux Vesta LED-modules that have 2 different color temperature LED rows.
i have a few of these i want to run in parallel off my dimmable CC driver.

now here's the thing: i want to be able to control the color temperature with a slider (or similar), so that when it is in the middle both rows light up equally, and when i move the slider to either right or left only the cold- or warmwhite led rows are on. the current should just be gradually guided/divided to cold, warm or both LED rows.
what piece if electronic circuit or device would i need for that?
Thanks in advance for your help

[tazztone]

i guess the only easy way is to add a 4-position-switch. however this would only allow for toggling between cold, warm, both or OFF. not gradually adjust CCT.

do you see a way to get gradual CCT-transitioning using only 1 potentiometer or similar?

[ATPinMotion]

I've been thinking about trying the same thing.

I believe the simplest way to accomplish this is with two drivers and a linear 100k voltage divider (or 3 contact potentiometer) as the dimmer.

One driver gets the 2700k strip and the other gets the 5000k. The pot 'fades' between them.

[tazztone]

the simplest way to accomplish this is with two drivers and a linear 100k 3 contact potentiometer

theoretically it should have worked because when the pot is turned all the way "up" it has max resistance (ohm) over contact 1 and 2 but minimal resistance over 2 and 3. and when it's all the way turned down it's the opposite.

i guess it also depends on the driver used. anyway: with my TRP drivers it's not really possible to dim them inversely to each other with a single 3 contact potentiometer. as soon as i connect the second driver's dimming leads to the 2nd & 3rd contact of the potentiometer it dims differently (maybe because of voltage flow?).

guess it needs fully seperate driver and dimming circuits, which is lame. i bet there's a way somehow but since i have almost zero knowledge of electronics i can't think of one.

[ATPinMotion]

Interesting, pos to pin 2, negative 1 and 3?

[tazztone]

Interesting, pos to pin 2, negative 1 and 3?

i was not sure what u meant, but i changed polarity of the dimming wire on the potentiometer and now it works.

[ATPinMotion]

Good work! How does it look? (The light quality I mean)

Happy to be of assistance. I think setting the vesta's up the way you did is really slick. Frankly I'm surprised more people aren't doing this - maybe they are and just not talking about it..?

Personally I'm still waffling between the Vesta's and QB22 strips for a veg tent. Im just getting into LED's. Just got a 200watt COB fixture (20x 20watt cobs, run at half power), and it puts out a fair amount of heat, even at 160lm/w. Thinking anything I can do to up the efficiency will make for happier plants.

As much as I would like to run some veg trials on colour temperature, I'm thinking qb for the veg tent and Vesta's for my workshop!

[tazztone]

How does it look? (The light quality I mean)

it's really good. nice neutral CCT when both rows are used. actually i will be using the Vestas for photography/video/general lights as well as for starting plants indoor. i also have 2 F-series 4000K but they are CRI80 and therefore not as versatile.

when i first found the VESTAs i couldn't find a single forum entry anywhere on google.
but as you can see here among all LEDs with CRI90 and above vestas pretty much beats any COB (sorted by lm/$) on digikey (as of Oct. 2018)

if you are still not sure about which one to chose (F-series or Vesta) this graph by livinglight sure put it all together:

LM561c 3000k 80CRI vs VESTA (combined CCT)

[ATPinMotion]

Thanks for the info - interesting comparisons.

I think I will have to try both and see for myself!

[Marine2143]

Osram and NASA seem to like 2700k with uv, blue, and reds programable. They will have this system on the market next month. https://hortamericas.com/catalog/hortic ... tofy-rl-2/