Help me define some leds for a controlled lamp - Page 1
Forum section: electronics / projects

author: dansku
author_rank: Regular Contributor
timestamp: July 18, 2016, 08:09:19 pm
content: Hello guys, I am building a wifi controlled lamp (for fun, don't judge me).I am using an ESP12 for the control but my question is more about the right leds for the job.I have a 12v power supply (I would like to have something under 2.5A).The lamp should have 4 different leds, white, red, green and blue. Something similar to a LIFX lamp.On this website,http://sixes.net/rdcHQ/lab/lightmapping/lifx.htmlcould someone help me find similar leds? Does anyone know what are these leds?If the led work with like 3.4v, I want to put 4x in series, so that I don't need to use a resistor on them.Anyone have LED suggestions, that in the end the lamp would have around 1000 lumens?Thanks

author: ajb
author_rank: Super Contributor
timestamp: July 18, 2016, 08:39:20 pm
content: Quote from: dansku on July 18, 2016, 08:09:19 pmYou always want a resistor, or better yet a constant current driver. Otherwise at best the brightness of the LEDs will vary significantly with the supply voltage, or at worst your LEDs will blow up. Blue, green, and white LEDs tend to be around 3-3.3V, but red LEDs are closer to 2-2.2V, so you it would be tricky to match all four sets of LEDs to the supply voltage.QuoteIt depends, is that 1000 lumens when all four sets of LEDs are on? And if so, what sort of color balance among the four sets are you looking for? Or is that 1000 lumens at any hue and saturation (which would mean you would need 1000 lumens of red, plus 1000 lumens of green, etc)?

author: dansku
author_rank: Regular Contributor
timestamp: July 18, 2016, 09:34:11 pm
content: Thank you for the input, I will make sure I use a LED driver.By looking at the leds on the picture, do you have any idea on their specs?

author: dansku
author_rank: Regular Contributor
timestamp: July 19, 2016, 06:39:28 am
content: Quote from: ajb on July 18, 2016, 08:39:20 pmI think the 1000 lumens would be with everything turned on. (same as lifx).By looking at the LEDs, any idea which they may be?Thank you

author: ajb
author_rank: Super Contributor
timestamp: July 19, 2016, 06:37:22 pm
content: I have no idea. You have a ballpark idea of their specs, based on the number of individual LEDs in each color and the stated brightness of the bulb, so your best bet is probably to start looking through catalogs and seeing what looks right. Or, instead of trying to copy their design, why not come up with your own solution that meets your exact needs?

author: dansku
author_rank: Regular Contributor
timestamp: July 20, 2016, 08:27:50 am
content: Quote from: ajb on July 19, 2016, 06:37:22 pmYeah I will do that, I am just trying to study more the way they did it. I wonder what's the power of the LEDs. Thanks

author: Corporate666
author_rank: Unknown
timestamp: July 21, 2016, 12:14:34 am
content: The white LED's are probably around 100 lumens each, which would make them around 1 watt LED's.As for the colored ones, they are probably something more like 1/2 watt or 1/3rd watt, just based on the package and die size.Are you doing this just for a personal project or is this something you are planning to commercialize? I do commercial white and color LED lighting, and there is quite a lot involved in doing it if you're planning to sell it and have it be good, vs just doing it for home use.One issue is color mixing. You need 3:6:1 (roughly) rations of red, green and blue to get white. Green LED's are more efficient than red or blue - so that's why you see so many red LED's on the PCB compared to the other two colors. Color mixing is very tricky to get right, because the LED's will shift color and intensity with temperature and voltage, and also with age. It's also difficult to control the intensity evenly to get good color mixing, especially without losing tons of the light you're generating.White is also tricky. Warmer color temperature LED's are less efficient. It's tempting to use neutral white LED's and then use the RGB LED's to vary color temperature, but I haven't seen this done where it generates a good quality (high CRI) light. Philips developed their lime green Rebel LED for this exact reason - and they use it in the Hue bulb which generates its white solely from color mixing. But at the cost of being able to produce deep greens and blues. Color temperature of white LED's will also shift over time and temperature. The Smithsonian in the USA famously switched to LED lights, only to have them all look different (some drifted blue, some pink, some green, some yellow) over time. It's also not as simple are just buying white LED's of a given color temperature and using them. They are binned into MacAdam ellipses. If your 3,000K LED's range from 2,500K to 3,500K, that will be noticeable. You also need to consider stuff like LM80 testing to get an idea of the lifetime of the LED's and how they will perform over the long haul.There are LED color mixing chips which use a sensor to detect the actual light being produced and can correct for color/intensity drift of the LED's across a temperature range. They aren't cheap, but if you're doing this commercially, they are worthwhile.I would look at Philips Lumileds stuff. Their Rebel LED's are fantastic when it comes to white light, and colors too. You could copy what Philips did with the Hue and use their lime green for color mixing to get white light since they sell the lime green LED now. I just started using the 3535 LED's from them and they are fantastic - around 130 lumens/watt @ 90CRI in warm white.Cree obviously is another one to look at, I use their XBD LED's and like them. Issue with Cree is they give you a thousand part numbers with various bins, CRI and color options - but 95% of all of them are vaporware that you can only get if you order 100,000pcs or some such, whereas Philips/Lumileds you can buy off the shelf all day long in small quantities.The other LED to look at is the Samsung 561B and it's family (561+ and 561C, etc). They are very efficient and have good color consistency over the long haul. Using efficient LED's is important, because the more efficient the LED, the less heat per unit light you are generating. And heat is the enemy of LED lighting. It messes up your color, it kills LED life and it makes fixture design a huge pain in the ass.Probably an overload of info but hope it helps.

author: dansku
author_rank: Regular Contributor
timestamp: July 24, 2016, 09:31:14 am
content: Quote from: Corporate666 on July 21, 2016, 12:14:34 amThank you for this amazing post, a lot of good information helped me to learn more about leds and light!From LUMILEDS I was looking at these ones:http://www.lumileds.com/products/high-power-leds/luxeon-txWhat do you think of them?But actually I may go with OSRAM, check this one:http://www.osram-os.com/osram_os/en/products/product-catalog/leds-for-general-lighting/duris-p-8/gw-pusra1.pm/index.jspI think they can be a good replacement for the Lumileds leds.Talking about LED drivers, I want to have RGBW so 4 channels, any recommendation for led drivers with pwm function that you'd suggest?Thank you!