Tunable color temperature LED lighting - Fancy RGBW LEDs or is there more to it? - Page 1
Forum section: electronics / projects

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: September 28, 2017, 02:06:57 pm
content: Various companies such as philips and ikea have LED lightbulbs where you can control the color temperature. Do these lights just use a RGB or more likely RGBW LED, or is there more too it? I would imagine using RGB or RGBW would give very poor CRI?

author: CJay
author_rank: Super Contributor
timestamp: September 28, 2017, 02:19:45 pm
content: Some just have two different colour temperature white LEDs and dim/brighten them to achieve 'warmer' or colder light.

author: DaJMasta
author_rank: Super Contributor
timestamp: September 28, 2017, 03:06:25 pm
content: In reef aquarium fixtures it's common to find a very wide mix, in addition to warm and cool white, they'll frequently have red, blue, UV, or green to mix in to cover more of the spectrum and allow for more adjustment (these fixtures also often have blues-only actinic modes), but I wouldn't be surprised if it was just a warm/cold color temperature mix if it's only variations of white. If they had full RGBs, then you'd expect to get every other available, while a niche use, it would be effectively already implemented if you were controlling color temperature with them.

author: Kjelt
author_rank: Super Contributor
timestamp: September 28, 2017, 03:21:04 pm
content: Hue has very good warm and cold white even in their full color bulbs, i had not expected that but use them now mostly for warm whites. If there is a party the other colours are usedTry them, if you only need white there are cheaper hue white alternatives. Poor CRI is common with led products since CRI is based on halogen (wide spectrum) bulbs, the industry is working on an alternative quality standard.One hue bulb broke and IIRC there were R(YG)B(CW)(WW) leds on it.

author: ajb
author_rank: Super Contributor
timestamp: September 28, 2017, 05:18:16 pm
content: Quote from: TheUnnamedNewbie on September 28, 2017, 02:06:57 pmPoor CRI is kind of an understatement for RGB "white". The more discontinuous the emission spectrum is, the more likely it is that you'll have ugly interactions with the pigmentation of the objects you're illuminating. Ideally for a color-changing luminaire you'd want as many constituent wavelengths as possible, which is why some stage lighting LED fixtures have seven or so different colors, not even counting white. If you just want to adjust the color temperature, two or more color temperatures of white LEDs is going to be the best and most cost effective way of doing that. There are some TV/film light fixtures that work exactly this way, which are really just modern replacements for fixtures that had multiple sets of fluorescent tubes in different color temperatures--of course with the LED version, you get infinite(ish) variation from one color temperature to the other, versus just one/the other/both.

author: khs
author_rank: Regular Contributor
timestamp: September 29, 2017, 08:38:47 am
content: Quote from: TheUnnamedNewbie on September 28, 2017, 02:06:57 pmYou can make a DIY spectrometer with a CD and make your own measurements.Unfortunately in German, but all you need is the picture.http://www.dpg-physik.de/dpg/gliederung/junge/mint/index.html?print=true&

author: tooki
author_rank: Super Contributor
timestamp: September 29, 2017, 03:52:44 pm
content: Quote from: CJay on September 28, 2017, 02:19:45 pmYep, this. You can now buy WW+CW led strips from eBay easily, as well as controllers for them.

author: maukka
author_rank: Unknown
timestamp: October 02, 2017, 10:43:13 am
content: I measured theIkea Trädfri LED bulb(E27, 980 lumens) to quite closely match their color temperature specification of 2200/2700/4000K. Just a quick test bouncing the light via the ceiling, not true integration in a sphere.They use separate LEDs for different temperatures and the CRI(Ra) is//respectively.I didn't open it up but I suppose the middle mode is generated by adding some of the cooler white LED output to the warm white LEDs. The output is 14% brighter than on the low temperature mode. They use PWM for brightness control so the tint doesn't change when the output is adjusted.Here's how they look plotted on a CIE(xy) chart relative to the black body radiator line.