Choosing LED for lamp - Page 1
Forum section: electronics / beginners

author: djacobow
author_rank: Super Contributor
timestamp: October 01, 2015, 07:57:17 pm
content: I'm posting in beginners because this is a beginner question, though I'm not exactly.tl;dr:I'm looking for help choosing a 10W-ish LED module suitable for a regular desk lamp. Just plain LEDs (not psu or anything) but with a diffuse isotropic radiation pattern. Basically, a lightbulb.So, about a year or so ago I started experimenting with all manner of light dimming. One of my ideas was to make a desk lamp for a child's bedroom that would start at full brightness but dim down slowly over a set interval until it reached nightlight levels. This was for helping kids get to sleep who are afraid of the dark. I originally started with triac dimming of a regular incandescent light, and though this worked just fine, I realized that 1) mains AC devices in a curious kid's bedroom isn't great, and anyway, incandescents are for dinosaurs.So then I got the clever idea of doing this with LED but in the process I did something very stupid. In my excitement to get this project going, I designed a board, circular, to serve as the base of a lamp. On it was an attiny, power circuits, sound sensor (clap on), light sensor, moon-shaped array of LEDs for nightlight mode, etc. The dimming was high quality, 16b at a few kHz, etc. And while I was prototyping I used an MR16 style lamp for the main light. The base of the lamp would be wood, with the board mounted over it with standoffs, and acrylic over that. In the center would be a dowel onto which the LED would mount (somehow) and a lampshade would go on that.Then I started searching for the LED module that I would "really" use and realized I had made a huge mistake in not figuring that out first. I'm looking for something that can be mounted at the top of a lamp and which radiates in all directions, like an olde fashioned bulb. But as far as I can tell, that animal doesn't exist.So, that project died, but I'd still like to resurrect if I could find the right module. Any hints? Or is this the sort of thing you need to have the resources to custom design and spec?PS -- Of course, I could cannibalize an LED lightbulb, removing the circuitry and letting myself drive the LEDs. But that's pricey-ish and, I was hoping on making a few of these for friends.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: October 02, 2015, 02:24:34 am
content: I am liking these LEDs a lot. They are very efficient, have a wide angle, and are available in several different color temperatures.http://www.lumileds.com/uploads/402/DS203-pdfCombined with AP2502 current sink and driven at 80 mA DC max (using all four sinks in the chip for each LED), with PWM for dimming, a few of them in an array, inside a diffuser, might work well for your purpose. At 80mA they won't even need a heatsink.

author: hayatepilot
author_rank: Frequent Contributor
timestamp: October 02, 2015, 02:25:59 pm
content: You could use these filament LEDs. They have a very homogeneous light distribution.http://www.runlite.cn/userfiles/5cjerp755q19k1413258994.pdfBut they require high voltages (~75V).Greetings

author: djacobow
author_rank: Super Contributor
timestamp: October 02, 2015, 10:01:18 pm
content: Hmm, the filament thing looks very interesting. What a strange part.The chip LEDs are fine, but a bit raw material for what I was hoping. I'd still have to arrange them into a quasi-spherical blob and figure out how to diffuse them. Who knew the mechanical design for something as simple as a lamp would be so tricky.

author: ez24
author_rank: Super Contributor
timestamp: October 02, 2015, 10:32:14 pm
content: http://www.aliexpress.com/item/RGB-LED-Strip-5M-300Led-3528-SMD-24Key-IR-Remote-Controller-12V-2A-Power-Adapter-Flexible/1849234838.html?spm=2114.01020208.3.2.vcOmGK&ws_ab_test=201556_2,201527_2_71_72_73_74_75,0_0

author: alsetalokin4017
author_rank: Super Contributor
timestamp: October 03, 2015, 03:32:29 am
content: I put one MXA8-PW40-0000 in a ping-pong ball....

author: djacobow
author_rank: Super Contributor
timestamp: October 04, 2015, 07:30:07 pm
content: Quote from: wilfred on October 02, 2015, 10:21:27 pmAh, ok. I really didn't understand how to use the filaments or what they were intended for; now I get it. Yes, I think they could work for this application. The only drawback is the reasonably high drive voltage necessary -- not optimal for something intended for small child's room.What I'm starting to gather is that the once-common "desk lamp' doesn't seem poised to jump to the LED generation. If you google for finished products you will see plenty of task lighting, where LEDs are mounted to shine directly down on something. But the equivalent of a 60W bulb radiating isotropically does not exist *except* in the case of directly trying to be a drop-in to existing lamps.My idea of a low voltage lamp that is reasonably bright and which puts out a quality light seems a bit out of reach at the moment.

author: djacobow
author_rank: Super Contributor
timestamp: October 04, 2015, 07:31:17 pm
content: Quote from: ez24 on October 02, 2015, 10:32:14 pmI really do not care for this sorts of things. Crappy 8b pwm (if you're lucky) at ridiculously low frequencies, typically. You want a nice high quality dim with no flicker and a good white light at high brightness? You're mostly out of luck.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: October 04, 2015, 08:42:30 pm
content: Well, you seem to be rejecting all suggestions.QuoteI think you could design and build what you want for just a few dollars, and then you have a perfect market niche you could fill with a commercial product.Quote from: alsetalokin4017 on October 02, 2015, 02:24:34 am

author: ECEdesign
author_rank: Regular Contributor
timestamp: October 04, 2015, 08:55:14 pm
content: Take a look at Nichia LEDs they are High CRI (Color Rendition Index) great LEDs. The Nichia 219 would be a good place to start they likely have a few new models since I last looked on their site.

author: Kjelt
author_rank: Super Contributor
timestamp: October 04, 2015, 09:03:56 pm
content: Youre requirements of the lighting pattern are not so much a requirement for the led but more for the optics after the led. Optics is a science on its own and i don,t think you find many experts on this forum (electronics). That said the chance for you to design electronics, led optics and mechanics on your own that will 100% fullfill you,re requirements is low. My advice, Buy a retro led lamp for this project and start with a project with smaller challenges.

author: djacobow
author_rank: Super Contributor
timestamp: October 04, 2015, 11:04:18 pm
content: Quote from: Kjelt on October 04, 2015, 09:03:56 pmYes, I think you're right exactly. The optics side was more than I bargained. I guess I thought there'd be some module out there like this. As near as I can tell, there isn't.It's funny. Back in the day, anybody could make a lamp out of practically anything. They sold these lamp kits, which were basically a socket, switch, and a cord. If you could drill a hole in an object, it could be a lamp. What I didn't appreciate is that the engineering was in the bulb, which was highly engineered and thought out. Even the idea of a lamp shade that fits over a bulb. You can't just assume such a thing today.

author: Kjelt
author_rank: Super Contributor
timestamp: October 05, 2015, 10:11:17 am
content: It is all available for sale but you need to combine a lot of seperate sold parts:PCBLEDCollimator/lens or lightguides for directional light or guiding light in certain directionor a diffusorHeatsinkPower supply/led driver.Those all combined will give you one led lamp.Now for a single step in all these steps try to choose which collimator you need, in the picture there are only 20 of the more then 1000 possibilitiesanswer below:(yeah it is a trick question you do not need a collimator you need multiple leds in all directions and a good diffusor for your project but just to show you how enormous the amounts of choices there are)