Variable Color Temp. LED light panel (3000K-6000K) with Kelvin value LC display - Page 1
Forum section: electronics / projects

author: carlob
author_rank: Contributor
timestamp: October 11, 2016, 10:38:24 pm
content: I would like to make Variable Color Temperature LED light panel, so i need to construct panels PCB, Controller and display where operator could see Kelvin value.Actually, with a lot controllers available, i can just put any commercial controller, like this one:https://www.superbrightleds.com/moreinfo/single-color-dimmer-switches/variable-color-temperature-led-controller-w-wireless-rf-remote-7-ampschannel/3048/6264/for example.Esentially, you just need to balance in sync two dimmable source. Mean Well even have built in DALI compatible PWM dimmer, but i would also like to be able to know what kolor temperature operator have chosen.I know how to design PCB, and I have access to PCB machine. I would use Osram Duris 5 PCB LE Diodes with 2700, maybe 3000K and 5500-6000K. Duris 5 have CRI better then 95.But, there is the catch. I would like to have Kelvin value, in XYZZ format, like on examples bellow, in attachments.Any body have any idea how to make that kind od design most efficiently?Thanks a lot!

author: singapol
author_rank: Frequent Contributor
timestamp: October 12, 2016, 01:07:33 am
content: I don't know how useful or practical building a variable colour LED light panel will be if it's for photographic useperhaps as a mood kind of lighting in the home? The photographic kind is difficult because you can't trust what the LED manufacturer claims the colour temperature is so you have to characterise or test them to select.QuoteThis is the million dollar question.You will notice such commercial light panels are not cheap especially forprofessional photographic use. Technically you incorporate a colour temperature meter into the unit but how accurate is it?Funny there are apps for iphone that can measure light in kelvin but how accurate is it? you can read the theorybut how to make an accurate one? Best is buy a used colour temperature meter like from Minolta or others or brand new it's not cheap either. Minolta has stopped making the meters and a Korean company has taken overby putting their brand over meters. Check out B&H Photo for such examples. Now to measure colour temperature accurately you need a photospectrometer...check the prices on ebay.Building colour temperature meters is a closely guarded secret. Also check out chinese copy on Aliexpress. Good luck.Edit: Actually what the led lighting designer has done is using a look up table via a dac to dial in the kelvin temperature but the main thing is characterising the led eg. at what voltage and current is a given colour temperature but also take into account of aging so the important thing is measuring this colour temperatureaccurately and this takes alot of work. As a hobbyist a simple colour temperature meter will do if you are not particular about accuracy. Calibration of photospectrameter uses what is known as a black body reference.

author: carlob
author_rank: Contributor
timestamp: October 12, 2016, 04:34:13 pm
content: I will use Osram LED Duris E5. Osram is not some third world manufacturers. Theirs components are up to specifications.Of course, i will not incorporate any color meter or similar. Just a little bit of maths...Basically, i would like to convert the table from attachment in to a working system!Two Mean Well LED drivers with built in DALI dimmer, for example:Mean Well LCM-60DAhttp://eu.mouser.com/ProductDetail/Mean-Well/LCM-60DA/?qs=1vfYvNkoS0Wsiq2c8DKyoQ%3D%3Dwill drive two group of LEDs. One will drive warm and other will drive cold LE diodes.Varing intensity of those two drivers thru DALI interface, you will get desired light temperature.It's work that way, i know, i work with that kind of lights every day.I'm not EE, but i'm willing to learn. Just need some ideas what is easyest way to make this to work.Thanks.

author: carlob
author_rank: Contributor
timestamp: October 14, 2016, 05:48:25 pm
content: This is my first post, so if i made some mistake, moderators, please move my topic to appropriate forum.Tnx